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  • Is this a violation of the single responsiblity principle?

    - by L. Moser
    I have the following method and interface: public object ProcessRules(List<IRule> rules) { foreach(IRule rule in rules) { if(EvaluateExpression(rule.Exp) == true) return rule.Result; } //Some error handling here for not hitting any rules } public interface IRule { Expression Exp; Object Result; int Precedence; } Because rules have a precedence, they should actually never be processed out of order. This leads me with (I think) three solutions: Sort rules before passing them into the evaluator. Change the parameter type to something that enforces a sort order. Sort within the evaluator. I like option 3 because it always ensures that it is sorted and I like option 1 because it seems more cohesive. And option 2 seems like a good compromise. Is a scenario like this context specific/subjective, or is there really a best practice to be applied here?

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  • How can I back up my ubuntu system?

    - by Eloff
    I'm sure there's a lot of questions on here similar to this, and I've been reading them, but I still feel this warrants a new question. I want nightly, incremental backups (full disk images would waste a lot of space - unless compressed somehow.) Preferably rotating or deleting old backups when running out of space or after a fixed number of backups. I want to be able to quickly and painlessly restore my system from these backups. This is my first time running ubuntu as my main development machine and I know from my experience with it as a server and in virtual machines that I regularly manage to make it unbootable or damage it to the point of being unable to rescue it. So how would you recommend I do this? There are so many options out there I really don't know where to start. There seems to be a vocal school of thought that it's sufficient to backup your home directory and the list of installed packages from the package manager. I've already installed lots of things from source, or outside of the package manager (development tools, ides, compilers, graphics drivers, etc.) So at the very least, if I do not back up the operating system itself I need to grab all config files, all program binaries, all created but required files, etc. I'd rather backup too much than too little - an ubuntu install is tiny anyway. Also this drastically reduces the restore time, which would cost me more in my time than the extra storage space. I tried using Deja Dup to backup the root partition, excluding some things like /mnt /media /dev /proc etc. Although many websites assured me you can backup a running linux system this way - that seems to be false as it complained that it could not backup the following files: /boot/System.map-3.0.0-17-generic /boot/System.map-3.2.0-22-generic /boot/vmcoreinfo-3.0.0-17-generic /boot/vmlinuz-3.0.0-17-generic /boot/vmlinuz-3.2.0-22-generic /etc/.pwd.lock /etc/NetworkManager/system-connections/LAN Connection /etc/apparmor.d/cache/lightdm-guest-session /etc/apparmor.d/cache/sbin.dhclient /etc/apparmor.d/cache/usr.bin.evince /etc/apparmor.d/cache/usr.lib.telepathy /etc/apparmor.d/cache/usr.sbin.cupsd /etc/apparmor.d/cache/usr.sbin.tcpdump /etc/apt/trustdb.gpg /etc/at.deny /etc/ati/inst_path_default /etc/ati/inst_path_override /etc/chatscripts /etc/cups/ssl /etc/cups/subscriptions.conf /etc/cups/subscriptions.conf.O /etc/default/cacerts /etc/fuse.conf /etc/group- /etc/gshadow /etc/gshadow- /etc/mtab.fuselock /etc/passwd- /etc/ppp/chap-secrets /etc/ppp/pap-secrets /etc/ppp/peers /etc/security/opasswd /etc/shadow /etc/shadow- /etc/ssl/private /etc/sudoers /etc/sudoers.d/README /etc/ufw/after.rules /etc/ufw/after6.rules /etc/ufw/before.rules /etc/ufw/before6.rules /lib/ufw/user.rules /lib/ufw/user6.rules /lost+found /root /run/crond.reboot /run/cups/certs /run/lightdm /run/lock/whoopsie/lock /run/udisks /var/backups/group.bak /var/backups/gshadow.bak /var/backups/passwd.bak /var/backups/shadow.bak /var/cache/apt/archives/lock /var/cache/cups/job.cache /var/cache/cups/job.cache.O /var/cache/cups/ppds.dat /var/cache/debconf/passwords.dat /var/cache/ldconfig /var/cache/lightdm/dmrc /var/crash/_usr_lib_x86_64-linux-gnu_colord_colord.102.crash /var/lib/apt/lists/lock /var/lib/dpkg/lock /var/lib/dpkg/triggers/Lock /var/lib/lightdm /var/lib/mlocate/mlocate.db /var/lib/polkit-1 /var/lib/sudo /var/lib/urandom/random-seed /var/lib/ureadahead/pack /var/lib/ureadahead/run.pack /var/log/btmp /var/log/installer/casper.log /var/log/installer/debug /var/log/installer/partman /var/log/installer/syslog /var/log/installer/version /var/log/lightdm/lightdm.log /var/log/lightdm/x-0-greeter.log /var/log/lightdm/x-0.log /var/log/speech-dispatcher /var/log/upstart/alsa-restore.log /var/log/upstart/alsa-restore.log.1.gz /var/log/upstart/console-setup.log /var/log/upstart/console-setup.log.1.gz /var/log/upstart/container-detect.log /var/log/upstart/container-detect.log.1.gz /var/log/upstart/hybrid-gfx.log /var/log/upstart/hybrid-gfx.log.1.gz /var/log/upstart/modemmanager.log /var/log/upstart/modemmanager.log.1.gz /var/log/upstart/module-init-tools.log /var/log/upstart/module-init-tools.log.1.gz /var/log/upstart/procps-static-network-up.log /var/log/upstart/procps-static-network-up.log.1.gz /var/log/upstart/procps-virtual-filesystems.log /var/log/upstart/procps-virtual-filesystems.log.1.gz /var/log/upstart/rsyslog.log /var/log/upstart/rsyslog.log.1.gz /var/log/upstart/ureadahead.log /var/log/upstart/ureadahead.log.1.gz /var/spool/anacron/cron.daily /var/spool/anacron/cron.monthly /var/spool/anacron/cron.weekly /var/spool/cron/atjobs /var/spool/cron/atspool /var/spool/cron/crontabs /var/spool/cups

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  • Combining Scrum, TFS2010 and Email to keep everyone in the loop

    - by Martin Hinshelwood
    Often you will receive rich information from your Product Owner (Customer) about tasks. That information can be in the form of Word documents, HTML Emails and Pictures, but you generally receive them in the context of an Email. You need to keep these so your Team can refer to it later, and so you can send a “done” when the task has been completed. This preserves the “history” of the task and allows you to keep relevant partied included in any future conversation. At SSW we keep the original email so that we can reply Done and delete the email. But keeping it in your email does not help other members of the team if they complete the task and need to send the “done”. Worse yet, the description field in Team Foundation Server 2010 (TFS 2010) does not support HTML and images, nor does the default task template support an “interested parties” or CC field. You can attach this content manually, but it can be time consuming. Figure: Description only supports plain text, and History supports HTML with no images   What should we do? At SSW we always follow the rules, and it just so happened that we have rules to both achieve this, and to make it easier. You should follow the existing Rules to Better Project Management  and attach the email to your task so you can refer to and reply to it later when you close the task: Do you know what Outlook add-ins you need? Describe the work item request in an email Use Outlook Add-in to move the email to a TFS Work Item When replying to an email with “done” you should follow: Do you update Team Companion template, so the email "subject" doesn't change? Do you update Team Companion template, so you can generate a proper "done" mail? Following these simple rules will help your Product Owner understand you better, and allow your team to more effectively collaborate with each other. An added bonus is that as we are keeping the email history in sync with TFS. When you “reply all” to the email all of the interested partied to the Task are also included. This notified those that may have been blocked by your task to keep up to date with its status. This has been published as Do you know to ensure that relevant emails are attached to tasks in our Rules to Better Scrum using TFS. What could we do better? I would like to see this process automated so that we capture the information correctly in the task without the need to use email. This would require a change to the process template in Team Foundation Server to add an “Interested Parties” field. Each reply to the email would need to be automatically processed into a Work Item. This could be done by adding a task identifier as the first item in the “Relates to” email header, and copying in an email address that you watch. This would then parse out the relevant information and add the new message to the history, update the “Interested parties” field and attach the Images. Upon reflection, it may even be possible, but more difficult to do this using ONLY the History field and including some of the header information in there to the build a done email with history. This would not currently deal with email “forks” well, but I think it would be adequate for our needs. It would be nice if we could find time to implement this, but currently it is but a pipe dream. Maybe Microsoft could implement something in the next version of Team Foundation Server, and in the mean time we have a process that works well. Technorati Tags: Scrum,SSW Rules,TFS 2010,TFS 2008

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  • Combining template method with strategy

    - by Mekswoll
    An assignment in my software engineering class is to design an application which can play different forms a particular game. The game in question is Mancala, some of these games are called Wari or Kalah. These games differ in some aspects but for my question it's only important to know that the games could differ in the following: The way in which the result of a move is handled The way in which the end of the game is determined The way in which the winner is determined The first thing that came to my mind to design this was to use the strategy pattern, I have a variation in algorithms (the actual rules of the game). The design could look like this: I then thought to myself that in the game of Mancala and Wari the way the winner is determined is exactly the same and the code would be duplicated. I don't think this is by definition a violation of the 'one rule, one place' or DRY principle seeing as a change in rules for Mancala wouldn't automatically mean that rule should be changed in Wari as well. Nevertheless from the feedback I got from my professor I got the impression to find a different design. I then came up with this: Each game (Mancala, Wari, Kalah, ...) would just have attribute of the type of each rule's interface, i.e. WinnerDeterminer and if there's a Mancala 2.0 version which is the same as Mancala 1.0 except for how the winner is determined it can just use the Mancala versions. I think the implementation of these rules as a strategy pattern is certainly valid. But the real problem comes when I want to design it further. In reading about the template method pattern I immediately thought it could be applied to this problem. The actions that are done when a user makes a move are always the same, and in the same order, namely: deposit stones in holes (this is the same for all games, so would be implemented in the template method itself) determine the result of the move determine if the game has finished because of the previous move if the game has finished, determine who has won Those three last steps are all in my strategy pattern described above. I'm having a lot of trouble combining these two. One possible solution I found would be to abandon the strategy pattern and do the following: I don't really see the design difference between the strategy pattern and this? But I am certain I need to use a template method (although I was just as sure about having to use a strategy pattern). I also can't determine who would be responsible for creating the TurnTemplate object, whereas with the strategy pattern I feel I have families of objects (the three rules) which I could easily create using an abstract factory pattern. I would then have a MancalaRuleFactory, WariRuleFactory, etc. and they would create the correct instances of the rules and hand me back a RuleSet object. Let's say that I use the strategy + abstract factory pattern and I have a RuleSet object which has algorithms for the three rules in it. The only way I feel I can still use the template method pattern with this is to pass this RuleSet object to my TurnTemplate. The 'problem' that then surfaces is that I would never need my concrete implementations of the TurnTemplate, these classes would become obsolete. In my protected methods in the TurnTemplate I could just call ruleSet.determineWinner(). As a consequence, the TurnTemplate class would no longer be abstract but would have to become concrete, is it then still a template method pattern? To summarize, am I thinking in the right way or am I missing something easy? If I'm on the right track, how do I combine a strategy pattern and a template method pattern? This is part of a homework assignment but I'm not looking to be gifted the answer, I have deliberately been very verbose in my question to show that I have thought about it before coming here to ask a question

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  • Is Oracle Policy Automation a Fit for My Agency? I'll bet it is.

    - by jeffrey.waterman
    Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin-top:0in; mso-para-margin-right:0in; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0in; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} Recently, I stumbled upon a new(-ish) whitepaper now posted on the Oracle Technology Network around Oracle Policy Automation (OPA). This paper is certain to become a must read for any customer interested in rules automation. What is OPA?  If you are not sitting in your favorite Greek restaurant waiting for that order of Saganaki to appear, OPA is Oracle’s solution for automated streamlining, standardizing, and the maintenance of policy. It is a specialized rules platform that simplifies the automation of rules and policies, putting the analysis in the hands of the analysts, not the IT organization. In other words, OPA allows the organization to be more efficient by eliminating (or at a minimum, reducing the engagement of) the middle man from the process. The whitepaper I mention above is titled, “Is Oracle Policy Automation a Good Fit for My Business?”. This short document walks the reader through use cases and advice for the reader to consider when deciding if OPA is right for their agency. The paper outlines many different scenarios, different uses of OPA in production today and, where OPA may not be a good fit. Many of the use case examples revolve around end user questionnaires or analyst research. What is often overlooked is OPA’s ability to act as a rules engine behind the scenes. That is, take inputs from one source (e.g., personnel data), process that data in OPA and send the output (e.g., pay data with benefits deductions) to a second source. The rules have been automated, no necessary human intervention to perform analysis. A few of my customers have used the embedded OPA solution to improve transaction processing and reduce the time spent analyzing exceptions. I suggest any reader whose organization is reliant on or deals with high complexity, volume or volatility in rules that are based on documentation – or which need to be documented – take a look at Oracle Policy Automation. You can find the white paper on Oracle Technology Network. You can find the white paper in the Oracle Policy Automation of the OTN. You can find more information around OPA on oracle.com. Finally, you can send me a question any time at [email protected] Thank you for reading. If you have any topics around Oracle Applications in the Federal or Public Sector industries you would like to see addressed in this blog, please leave suggestions in the comments section and I will do my best to address in a future post.

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  • VirtualBox Clone Root HD / Ubuntu / Network issue

    - by john.graves(at)oracle.com
    When you clone a root Ubuntu disk in VirtualBox, one thing that gets messed up is the network card definition.  This is because Ubuntu (as it should) uses UDEV IDs for the network device.  When you boot your new disk, the network device ID has changed, so it creates a new eth1 device.  Unfortunately, this conflicts with the VirtualBox network setup.  What to do? Boot the box (no network) Edit the /etc/udev/rules.d/70-persistent-net.rules Delete the eth0 line and modify the eth1 line to be eth0 --------- Example OLD ----------- # This file was automatically generated by the /lib/udev/write_net_rules # program, run by the persistent-net-generator.rules rules file. # # You can modify it, as long as you keep each rule on a single # line, and change only the value of the NAME= key. # PCI device 0x8086:0x100e (e1000) <-------------------- Delete these two lines SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="08:00:27:d8:8d:15", ATTR{dev_id}=="0x0", ATTR{type}=="1", KERNEL=="eth*", NAME="eth0" # PCI device 0x8086:0x100e (e1000) ---Modify the next line and change eth1 to be eth0 SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="08:00:27:89:84:98", ATTR{dev_id}=="0x0", ATTR{type}=="1", KERNEL=="eth*", NAME="eth1" .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } ---------------------------------------- --------- Example NEW ----------- # This file was automatically generated by the /lib/udev/write_net_rules # program, run by the persistent-net-generator.rules rules file. # # You can modify it, as long as you keep each rule on a single # line, and change only the value of the NAME= key. # PCI device 0x8086:0x100e (e1000) SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="08:00:27:89:84:98", ATTR{dev_id}=="0x0", ATTR{type}=="1", KERNEL=="eth*", NAME="eth0" .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } ----------------------------------------

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  • Something about Property Management or &hellip; the understanding of SharePoint Admins/roles ?!?

    - by Enrique Lima
    When I talk about SharePoint, for some reason it comes to my mind as if it were property management and all the tasks associated with it. So, imagine you have a lot ( a piece of land of sorts), you then decide there is something you want to do with it.  So, you make the choice of having a building built.  Now, in order to go forward with your plan, you need to check what the rules/regulations are.  Has is it been zoned residential, commercial, industrial … you get the idea.  This to me sounds like Governance.  The what am I to do given a defined set of rules. We keep on moving forward based on those rules.  And with this we start the process of building, the building process takes us to survey the land, identify what our boundaries are.  And as we go along we start getting the idea in our head as to what we will do as far as the building goes.  We identify the essentials of the building, basic services and such.  All in all, we plan.  And as with many things we do, we like solid foundations.  What a solid foundation looks like will depend on where and what we build.  The way buildings are built depends in many ways in being able to foresee the potential for natural disasters or to try to leverage the lay of the land.  Sound familiar?  We have done our Requirements Gathering. We have the building in place, we have followed the zoning rules, we have implemented services.  But we need someone to manage the building, now we move on to the human side of the story.  We want to establish a means to normalcy in the building, someone that can be the monitoring agent as to the “what’s going on?” of it.  This person will be tasked with making sure all basic services are functional, that measures are taken if there is an issue and so on.  Enter the Farm Administrator. In a way, we establish an extension of the rules to make sure the building and the apartments/offices build follow a standard set of rules too. Now, in turn you will have people leasing or buying the apartments/offices, they will be the keepers of that space.  So, now we are building sites, we have moved from having the building (farm) ready, to leasing/selling offices/apartments (site collections).  There will be someone assuming responsibility for those offices, that person will authorize or be informed about activities and also who not only gets a code into the building, but perhaps a key to the office.  Enter Site Collection Administrator.  And then perhaps we move on to the person that would be responsible for specifics within the office, for example a Human Resources Manager or Coordinator.  They will have specific control and knowledge about people.  A facilities coordinator, and so on.  I would translate that into Site Administrators. With that said then, we identify the following: Role Name Responsibility (but not limited to) Farm Administrator Infrastructure Site Collection Admin Policies for Content, Hierarchy, Recycle Bin, Security and Access Site Owner (Site Admin) Security and Access, Training, Guidance, Manage Templates All in all there are different levels of responsibility to be handled, but it is very important to understand what they are and what they mean. Here is a link to very well laid out explanation on this … http://www.endusersharepoint.com/2009/08/11/site-managers-and-end-user-expectations-roles-and-responsibilities/

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  • Why is x=x++ undefined?

    - by ugoren
    It's undefined because the it modifies x twice between sequence points. The standard says it's undefined, therefore it's undefined. That much I know. But why? My understanding is that forbidding this allows compilers to optimize better. This could have made sense when C was invented, but now seems like a weak argument. If we were to reinvent C today, would we do it this way, or can it be done better? Or maybe there's a deeper problem, that makes it hard to define consistent rules for such expressions, so it's best to forbid them? So suppose we were to reinvent C today. I'd like to suggest simple rules for expressions such as x=x++, which seem to me to work better than the existing rules. I'd like to get your opinion on the suggested rules compared to the existing ones, or other suggestions. Suggested Rules: Between sequence points, order of evaluation is unspecified. Side effects take place immediately. There's no undefined behavior involved. Expressions evaluate to this value or that, but surely won't format your hard disk (strangely, I've never seen an implementation where x=x++ formats the hard disk). Example Expressions x=x++ - Well defined, doesn't change x. First, x is incremented (immediately when x++ is evaluated), then it's old value is stored in x. x++ + ++x - Increments x twice, evaluates to 2*x+2. Though either side may be evaluated first, the result is either x + (x+2) (left side first) or (x+1) + (x+1) (right side first). x = x + (x=3) - Unspecified, x set to either x+3 or 6. If the right side is evaluated first, it's x+3. It's also possible that x=3 is evaluated first, so it's 3+3. In either case, the x=3 assignment happens immediately when x=3 is evaluated, so the value stored is overwritten by the other assignment. x+=(x=3) - Well defined, sets x to 6. You could argue that this is just shorthand for the expression above. But I'd say that += must be executed after x=3, and not in two parts (read x, evaluate x=3, add and store new value). What's the Advantage? Some comments raised this good point. It's not that I'm after the pleasure of using x=x++ in my code. It's a strange and misleading expression. What I want is to be able to understand complicated expressions. Normally, a complicated expression is no more than the sum of its parts. If you understand the parts and the operators combining them, you can understand the whole. C's current behavior seems to deviate from this principle. One assignment plus another assignment suddenly doesn't make two assignments. Today, when I look at x=x++, I can't say what it does. With my suggested rules, I can, by simply examining its components and their relations.

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  • value types in the vm

    - by john.rose
    value types in the vm p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Times} p.p2 {margin: 0.0px 0.0px 14.0px 0.0px; font: 14.0px Times} p.p3 {margin: 0.0px 0.0px 12.0px 0.0px; font: 14.0px Times} p.p4 {margin: 0.0px 0.0px 15.0px 0.0px; font: 14.0px Times} p.p5 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Courier} p.p6 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Courier; min-height: 17.0px} p.p7 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Times; min-height: 18.0px} p.p8 {margin: 0.0px 0.0px 0.0px 36.0px; text-indent: -36.0px; font: 14.0px Times; min-height: 18.0px} p.p9 {margin: 0.0px 0.0px 12.0px 0.0px; font: 14.0px Times; min-height: 18.0px} p.p10 {margin: 0.0px 0.0px 12.0px 0.0px; font: 14.0px Times; color: #000000} li.li1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Times} li.li7 {margin: 0.0px 0.0px 0.0px 0.0px; font: 14.0px Times; min-height: 18.0px} span.s1 {font: 14.0px Courier} span.s2 {color: #000000} span.s3 {font: 14.0px Courier; color: #000000} ol.ol1 {list-style-type: decimal} Or, enduring values for a changing world. Introduction A value type is a data type which, generally speaking, is designed for being passed by value in and out of methods, and stored by value in data structures. The only value types which the Java language directly supports are the eight primitive types. Java indirectly and approximately supports value types, if they are implemented in terms of classes. For example, both Integer and String may be viewed as value types, especially if their usage is restricted to avoid operations appropriate to Object. In this note, we propose a definition of value types in terms of a design pattern for Java classes, accompanied by a set of usage restrictions. We also sketch the relation of such value types to tuple types (which are a JVM-level notion), and point out JVM optimizations that can apply to value types. This note is a thought experiment to extend the JVM’s performance model in support of value types. The demonstration has two phases.  Initially the extension can simply use design patterns, within the current bytecode architecture, and in today’s Java language. But if the performance model is to be realized in practice, it will probably require new JVM bytecode features, changes to the Java language, or both.  We will look at a few possibilities for these new features. An Axiom of Value In the context of the JVM, a value type is a data type equipped with construction, assignment, and equality operations, and a set of typed components, such that, whenever two variables of the value type produce equal corresponding values for their components, the values of the two variables cannot be distinguished by any JVM operation. Here are some corollaries: A value type is immutable, since otherwise a copy could be constructed and the original could be modified in one of its components, allowing the copies to be distinguished. Changing the component of a value type requires construction of a new value. The equals and hashCode operations are strictly component-wise. If a value type is represented by a JVM reference, that reference cannot be successfully synchronized on, and cannot be usefully compared for reference equality. A value type can be viewed in terms of what it doesn’t do. We can say that a value type omits all value-unsafe operations, which could violate the constraints on value types.  These operations, which are ordinarily allowed for Java object types, are pointer equality comparison (the acmp instruction), synchronization (the monitor instructions), all the wait and notify methods of class Object, and non-trivial finalize methods. The clone method is also value-unsafe, although for value types it could be treated as the identity function. Finally, and most importantly, any side effect on an object (however visible) also counts as an value-unsafe operation. A value type may have methods, but such methods must not change the components of the value. It is reasonable and useful to define methods like toString, equals, and hashCode on value types, and also methods which are specifically valuable to users of the value type. Representations of Value Value types have two natural representations in the JVM, unboxed and boxed. An unboxed value consists of the components, as simple variables. For example, the complex number x=(1+2i), in rectangular coordinate form, may be represented in unboxed form by the following pair of variables: /*Complex x = Complex.valueOf(1.0, 2.0):*/ double x_re = 1.0, x_im = 2.0; These variables might be locals, parameters, or fields. Their association as components of a single value is not defined to the JVM. Here is a sample computation which computes the norm of the difference between two complex numbers: double distance(/*Complex x:*/ double x_re, double x_im,         /*Complex y:*/ double y_re, double y_im) {     /*Complex z = x.minus(y):*/     double z_re = x_re - y_re, z_im = x_im - y_im;     /*return z.abs():*/     return Math.sqrt(z_re*z_re + z_im*z_im); } A boxed representation groups component values under a single object reference. The reference is to a ‘wrapper class’ that carries the component values in its fields. (A primitive type can naturally be equated with a trivial value type with just one component of that type. In that view, the wrapper class Integer can serve as a boxed representation of value type int.) The unboxed representation of complex numbers is practical for many uses, but it fails to cover several major use cases: return values, array elements, and generic APIs. The two components of a complex number cannot be directly returned from a Java function, since Java does not support multiple return values. The same story applies to array elements: Java has no ’array of structs’ feature. (Double-length arrays are a possible workaround for complex numbers, but not for value types with heterogeneous components.) By generic APIs I mean both those which use generic types, like Arrays.asList and those which have special case support for primitive types, like String.valueOf and PrintStream.println. Those APIs do not support unboxed values, and offer some problems to boxed values. Any ’real’ JVM type should have a story for returns, arrays, and API interoperability. The basic problem here is that value types fall between primitive types and object types. Value types are clearly more complex than primitive types, and object types are slightly too complicated. Objects are a little bit dangerous to use as value carriers, since object references can be compared for pointer equality, and can be synchronized on. Also, as many Java programmers have observed, there is often a performance cost to using wrapper objects, even on modern JVMs. Even so, wrapper classes are a good starting point for talking about value types. If there were a set of structural rules and restrictions which would prevent value-unsafe operations on value types, wrapper classes would provide a good notation for defining value types. This note attempts to define such rules and restrictions. Let’s Start Coding Now it is time to look at some real code. Here is a definition, written in Java, of a complex number value type. @ValueSafe public final class Complex implements java.io.Serializable {     // immutable component structure:     public final double re, im;     private Complex(double re, double im) {         this.re = re; this.im = im;     }     // interoperability methods:     public String toString() { return "Complex("+re+","+im+")"; }     public List<Double> asList() { return Arrays.asList(re, im); }     public boolean equals(Complex c) {         return re == c.re && im == c.im;     }     public boolean equals(@ValueSafe Object x) {         return x instanceof Complex && equals((Complex) x);     }     public int hashCode() {         return 31*Double.valueOf(re).hashCode()                 + Double.valueOf(im).hashCode();     }     // factory methods:     public static Complex valueOf(double re, double im) {         return new Complex(re, im);     }     public Complex changeRe(double re2) { return valueOf(re2, im); }     public Complex changeIm(double im2) { return valueOf(re, im2); }     public static Complex cast(@ValueSafe Object x) {         return x == null ? ZERO : (Complex) x;     }     // utility methods and constants:     public Complex plus(Complex c)  { return new Complex(re+c.re, im+c.im); }     public Complex minus(Complex c) { return new Complex(re-c.re, im-c.im); }     public double abs() { return Math.sqrt(re*re + im*im); }     public static final Complex PI = valueOf(Math.PI, 0.0);     public static final Complex ZERO = valueOf(0.0, 0.0); } This is not a minimal definition, because it includes some utility methods and other optional parts.  The essential elements are as follows: The class is marked as a value type with an annotation. The class is final, because it does not make sense to create subclasses of value types. The fields of the class are all non-private and final.  (I.e., the type is immutable and structurally transparent.) From the supertype Object, all public non-final methods are overridden. The constructor is private. Beyond these bare essentials, we can observe the following features in this example, which are likely to be typical of all value types: One or more factory methods are responsible for value creation, including a component-wise valueOf method. There are utility methods for complex arithmetic and instance creation, such as plus and changeIm. There are static utility constants, such as PI. The type is serializable, using the default mechanisms. There are methods for converting to and from dynamically typed references, such as asList and cast. The Rules In order to use value types properly, the programmer must avoid value-unsafe operations.  A helpful Java compiler should issue errors (or at least warnings) for code which provably applies value-unsafe operations, and should issue warnings for code which might be correct but does not provably avoid value-unsafe operations.  No such compilers exist today, but to simplify our account here, we will pretend that they do exist. A value-safe type is any class, interface, or type parameter marked with the @ValueSafe annotation, or any subtype of a value-safe type.  If a value-safe class is marked final, it is in fact a value type.  All other value-safe classes must be abstract.  The non-static fields of a value class must be non-public and final, and all its constructors must be private. Under the above rules, a standard interface could be helpful to define value types like Complex.  Here is an example: @ValueSafe public interface ValueType extends java.io.Serializable {     // All methods listed here must get redefined.     // Definitions must be value-safe, which means     // they may depend on component values only.     List<? extends Object> asList();     int hashCode();     boolean equals(@ValueSafe Object c);     String toString(); } //@ValueSafe inherited from supertype: public final class Complex implements ValueType { … The main advantage of such a conventional interface is that (unlike an annotation) it is reified in the runtime type system.  It could appear as an element type or parameter bound, for facilities which are designed to work on value types only.  More broadly, it might assist the JVM to perform dynamic enforcement of the rules for value types. Besides types, the annotation @ValueSafe can mark fields, parameters, local variables, and methods.  (This is redundant when the type is also value-safe, but may be useful when the type is Object or another supertype of a value type.)  Working forward from these annotations, an expression E is defined as value-safe if it satisfies one or more of the following: The type of E is a value-safe type. E names a field, parameter, or local variable whose declaration is marked @ValueSafe. E is a call to a method whose declaration is marked @ValueSafe. E is an assignment to a value-safe variable, field reference, or array reference. E is a cast to a value-safe type from a value-safe expression. E is a conditional expression E0 ? E1 : E2, and both E1 and E2 are value-safe. Assignments to value-safe expressions and initializations of value-safe names must take their values from value-safe expressions. A value-safe expression may not be the subject of a value-unsafe operation.  In particular, it cannot be synchronized on, nor can it be compared with the “==” operator, not even with a null or with another value-safe type. In a program where all of these rules are followed, no value-type value will be subject to a value-unsafe operation.  Thus, the prime axiom of value types will be satisfied, that no two value type will be distinguishable as long as their component values are equal. More Code To illustrate these rules, here are some usage examples for Complex: Complex pi = Complex.valueOf(Math.PI, 0); Complex zero = pi.changeRe(0);  //zero = pi; zero.re = 0; ValueType vtype = pi; @SuppressWarnings("value-unsafe")   Object obj = pi; @ValueSafe Object obj2 = pi; obj2 = new Object();  // ok List<Complex> clist = new ArrayList<Complex>(); clist.add(pi);  // (ok assuming List.add param is @ValueSafe) List<ValueType> vlist = new ArrayList<ValueType>(); vlist.add(pi);  // (ok) List<Object> olist = new ArrayList<Object>(); olist.add(pi);  // warning: "value-unsafe" boolean z = pi.equals(zero); boolean z1 = (pi == zero);  // error: reference comparison on value type boolean z2 = (pi == null);  // error: reference comparison on value type boolean z3 = (pi == obj2);  // error: reference comparison on value type synchronized (pi) { }  // error: synch of value, unpredictable result synchronized (obj2) { }  // unpredictable result Complex qq = pi; qq = null;  // possible NPE; warning: “null-unsafe" qq = (Complex) obj;  // warning: “null-unsafe" qq = Complex.cast(obj);  // OK @SuppressWarnings("null-unsafe")   Complex empty = null;  // possible NPE qq = empty;  // possible NPE (null pollution) The Payoffs It follows from this that either the JVM or the java compiler can replace boxed value-type values with unboxed ones, without affecting normal computations.  Fields and variables of value types can be split into their unboxed components.  Non-static methods on value types can be transformed into static methods which take the components as value parameters. Some common questions arise around this point in any discussion of value types. Why burden the programmer with all these extra rules?  Why not detect programs automagically and perform unboxing transparently?  The answer is that it is easy to break the rules accidently unless they are agreed to by the programmer and enforced.  Automatic unboxing optimizations are tantalizing but (so far) unreachable ideal.  In the current state of the art, it is possible exhibit benchmarks in which automatic unboxing provides the desired effects, but it is not possible to provide a JVM with a performance model that assures the programmer when unboxing will occur.  This is why I’m writing this note, to enlist help from, and provide assurances to, the programmer.  Basically, I’m shooting for a good set of user-supplied “pragmas” to frame the desired optimization. Again, the important thing is that the unboxing must be done reliably, or else programmers will have no reason to work with the extra complexity of the value-safety rules.  There must be a reasonably stable performance model, wherein using a value type has approximately the same performance characteristics as writing the unboxed components as separate Java variables. There are some rough corners to the present scheme.  Since Java fields and array elements are initialized to null, value-type computations which incorporate uninitialized variables can produce null pointer exceptions.  One workaround for this is to require such variables to be null-tested, and the result replaced with a suitable all-zero value of the value type.  That is what the “cast” method does above. Generically typed APIs like List<T> will continue to manipulate boxed values always, at least until we figure out how to do reification of generic type instances.  Use of such APIs will elicit warnings until their type parameters (and/or relevant members) are annotated or typed as value-safe.  Retrofitting List<T> is likely to expose flaws in the present scheme, which we will need to engineer around.  Here are a couple of first approaches: public interface java.util.List<@ValueSafe T> extends Collection<T> { … public interface java.util.List<T extends Object|ValueType> extends Collection<T> { … (The second approach would require disjunctive types, in which value-safety is “contagious” from the constituent types.) With more transformations, the return value types of methods can also be unboxed.  This may require significant bytecode-level transformations, and would work best in the presence of a bytecode representation for multiple value groups, which I have proposed elsewhere under the title “Tuples in the VM”. But for starters, the JVM can apply this transformation under the covers, to internally compiled methods.  This would give a way to express multiple return values and structured return values, which is a significant pain-point for Java programmers, especially those who work with low-level structure types favored by modern vector and graphics processors.  The lack of multiple return values has a strong distorting effect on many Java APIs. Even if the JVM fails to unbox a value, there is still potential benefit to the value type.  Clustered computing systems something have copy operations (serialization or something similar) which apply implicitly to command operands.  When copying JVM objects, it is extremely helpful to know when an object’s identity is important or not.  If an object reference is a copied operand, the system may have to create a proxy handle which points back to the original object, so that side effects are visible.  Proxies must be managed carefully, and this can be expensive.  On the other hand, value types are exactly those types which a JVM can “copy and forget” with no downside. Array types are crucial to bulk data interfaces.  (As data sizes and rates increase, bulk data becomes more important than scalar data, so arrays are definitely accompanying us into the future of computing.)  Value types are very helpful for adding structure to bulk data, so a successful value type mechanism will make it easier for us to express richer forms of bulk data. Unboxing arrays (i.e., arrays containing unboxed values) will provide better cache and memory density, and more direct data movement within clustered or heterogeneous computing systems.  They require the deepest transformations, relative to today’s JVM.  There is an impedance mismatch between value-type arrays and Java’s covariant array typing, so compromises will need to be struck with existing Java semantics.  It is probably worth the effort, since arrays of unboxed value types are inherently more memory-efficient than standard Java arrays, which rely on dependent pointer chains. It may be sufficient to extend the “value-safe” concept to array declarations, and allow low-level transformations to change value-safe array declarations from the standard boxed form into an unboxed tuple-based form.  Such value-safe arrays would not be convertible to Object[] arrays.  Certain connection points, such as Arrays.copyOf and System.arraycopy might need additional input/output combinations, to allow smooth conversion between arrays with boxed and unboxed elements. Alternatively, the correct solution may have to wait until we have enough reification of generic types, and enough operator overloading, to enable an overhaul of Java arrays. Implicit Method Definitions The example of class Complex above may be unattractively complex.  I believe most or all of the elements of the example class are required by the logic of value types. If this is true, a programmer who writes a value type will have to write lots of error-prone boilerplate code.  On the other hand, I think nearly all of the code (except for the domain-specific parts like plus and minus) can be implicitly generated. Java has a rule for implicitly defining a class’s constructor, if no it defines no constructors explicitly.  Likewise, there are rules for providing default access modifiers for interface members.  Because of the highly regular structure of value types, it might be reasonable to perform similar implicit transformations on value types.  Here’s an example of a “highly implicit” definition of a complex number type: public class Complex implements ValueType {  // implicitly final     public double re, im;  // implicitly public final     //implicit methods are defined elementwise from te fields:     //  toString, asList, equals(2), hashCode, valueOf, cast     //optionally, explicit methods (plus, abs, etc.) would go here } In other words, with the right defaults, a simple value type definition can be a one-liner.  The observant reader will have noticed the similarities (and suitable differences) between the explicit methods above and the corresponding methods for List<T>. Another way to abbreviate such a class would be to make an annotation the primary trigger of the functionality, and to add the interface(s) implicitly: public @ValueType class Complex { … // implicitly final, implements ValueType (But to me it seems better to communicate the “magic” via an interface, even if it is rooted in an annotation.) Implicitly Defined Value Types So far we have been working with nominal value types, which is to say that the sequence of typed components is associated with a name and additional methods that convey the intention of the programmer.  A simple ordered pair of floating point numbers can be variously interpreted as (to name a few possibilities) a rectangular or polar complex number or Cartesian point.  The name and the methods convey the intended meaning. But what if we need a truly simple ordered pair of floating point numbers, without any further conceptual baggage?  Perhaps we are writing a method (like “divideAndRemainder”) which naturally returns a pair of numbers instead of a single number.  Wrapping the pair of numbers in a nominal type (like “QuotientAndRemainder”) makes as little sense as wrapping a single return value in a nominal type (like “Quotient”).  What we need here are structural value types commonly known as tuples. For the present discussion, let us assign a conventional, JVM-friendly name to tuples, roughly as follows: public class java.lang.tuple.$DD extends java.lang.tuple.Tuple {      double $1, $2; } Here the component names are fixed and all the required methods are defined implicitly.  The supertype is an abstract class which has suitable shared declarations.  The name itself mentions a JVM-style method parameter descriptor, which may be “cracked” to determine the number and types of the component fields. The odd thing about such a tuple type (and structural types in general) is it must be instantiated lazily, in response to linkage requests from one or more classes that need it.  The JVM and/or its class loaders must be prepared to spin a tuple type on demand, given a simple name reference, $xyz, where the xyz is cracked into a series of component types.  (Specifics of naming and name mangling need some tasteful engineering.) Tuples also seem to demand, even more than nominal types, some support from the language.  (This is probably because notations for non-nominal types work best as combinations of punctuation and type names, rather than named constructors like Function3 or Tuple2.)  At a minimum, languages with tuples usually (I think) have some sort of simple bracket notation for creating tuples, and a corresponding pattern-matching syntax (or “destructuring bind”) for taking tuples apart, at least when they are parameter lists.  Designing such a syntax is no simple thing, because it ought to play well with nominal value types, and also with pre-existing Java features, such as method parameter lists, implicit conversions, generic types, and reflection.  That is a task for another day. Other Use Cases Besides complex numbers and simple tuples there are many use cases for value types.  Many tuple-like types have natural value-type representations. These include rational numbers, point locations and pixel colors, and various kinds of dates and addresses. Other types have a variable-length ‘tail’ of internal values. The most common example of this is String, which is (mathematically) a sequence of UTF-16 character values. Similarly, bit vectors, multiple-precision numbers, and polynomials are composed of sequences of values. Such types include, in their representation, a reference to a variable-sized data structure (often an array) which (somehow) represents the sequence of values. The value type may also include ’header’ information. Variable-sized values often have a length distribution which favors short lengths. In that case, the design of the value type can make the first few values in the sequence be direct ’header’ fields of the value type. In the common case where the header is enough to represent the whole value, the tail can be a shared null value, or even just a null reference. Note that the tail need not be an immutable object, as long as the header type encapsulates it well enough. This is the case with String, where the tail is a mutable (but never mutated) character array. Field types and their order must be a globally visible part of the API.  The structure of the value type must be transparent enough to have a globally consistent unboxed representation, so that all callers and callees agree about the type and order of components  that appear as parameters, return types, and array elements.  This is a trade-off between efficiency and encapsulation, which is forced on us when we remove an indirection enjoyed by boxed representations.  A JVM-only transformation would not care about such visibility, but a bytecode transformation would need to take care that (say) the components of complex numbers would not get swapped after a redefinition of Complex and a partial recompile.  Perhaps constant pool references to value types need to declare the field order as assumed by each API user. This brings up the delicate status of private fields in a value type.  It must always be possible to load, store, and copy value types as coordinated groups, and the JVM performs those movements by moving individual scalar values between locals and stack.  If a component field is not public, what is to prevent hostile code from plucking it out of the tuple using a rogue aload or astore instruction?  Nothing but the verifier, so we may need to give it more smarts, so that it treats value types as inseparable groups of stack slots or locals (something like long or double). My initial thought was to make the fields always public, which would make the security problem moot.  But public is not always the right answer; consider the case of String, where the underlying mutable character array must be encapsulated to prevent security holes.  I believe we can win back both sides of the tradeoff, by training the verifier never to split up the components in an unboxed value.  Just as the verifier encapsulates the two halves of a 64-bit primitive, it can encapsulate the the header and body of an unboxed String, so that no code other than that of class String itself can take apart the values. Similar to String, we could build an efficient multi-precision decimal type along these lines: public final class DecimalValue extends ValueType {     protected final long header;     protected private final BigInteger digits;     public DecimalValue valueOf(int value, int scale) {         assert(scale >= 0);         return new DecimalValue(((long)value << 32) + scale, null);     }     public DecimalValue valueOf(long value, int scale) {         if (value == (int) value)             return valueOf((int)value, scale);         return new DecimalValue(-scale, new BigInteger(value));     } } Values of this type would be passed between methods as two machine words. Small values (those with a significand which fits into 32 bits) would be represented without any heap data at all, unless the DecimalValue itself were boxed. (Note the tension between encapsulation and unboxing in this case.  It would be better if the header and digits fields were private, but depending on where the unboxing information must “leak”, it is probably safer to make a public revelation of the internal structure.) Note that, although an array of Complex can be faked with a double-length array of double, there is no easy way to fake an array of unboxed DecimalValues.  (Either an array of boxed values or a transposed pair of homogeneous arrays would be reasonable fallbacks, in a current JVM.)  Getting the full benefit of unboxing and arrays will require some new JVM magic. Although the JVM emphasizes portability, system dependent code will benefit from using machine-level types larger than 64 bits.  For example, the back end of a linear algebra package might benefit from value types like Float4 which map to stock vector types.  This is probably only worthwhile if the unboxing arrays can be packed with such values. More Daydreams A more finely-divided design for dynamic enforcement of value safety could feature separate marker interfaces for each invariant.  An empty marker interface Unsynchronizable could cause suitable exceptions for monitor instructions on objects in marked classes.  More radically, a Interchangeable marker interface could cause JVM primitives that are sensitive to object identity to raise exceptions; the strangest result would be that the acmp instruction would have to be specified as raising an exception. @ValueSafe public interface ValueType extends java.io.Serializable,         Unsynchronizable, Interchangeable { … public class Complex implements ValueType {     // inherits Serializable, Unsynchronizable, Interchangeable, @ValueSafe     … It seems possible that Integer and the other wrapper types could be retro-fitted as value-safe types.  This is a major change, since wrapper objects would be unsynchronizable and their references interchangeable.  It is likely that code which violates value-safety for wrapper types exists but is uncommon.  It is less plausible to retro-fit String, since the prominent operation String.intern is often used with value-unsafe code. We should also reconsider the distinction between boxed and unboxed values in code.  The design presented above obscures that distinction.  As another thought experiment, we could imagine making a first class distinction in the type system between boxed and unboxed representations.  Since only primitive types are named with a lower-case initial letter, we could define that the capitalized version of a value type name always refers to the boxed representation, while the initial lower-case variant always refers to boxed.  For example: complex pi = complex.valueOf(Math.PI, 0); Complex boxPi = pi;  // convert to boxed myList.add(boxPi); complex z = myList.get(0);  // unbox Such a convention could perhaps absorb the current difference between int and Integer, double and Double. It might also allow the programmer to express a helpful distinction among array types. As said above, array types are crucial to bulk data interfaces, but are limited in the JVM.  Extending arrays beyond the present limitations is worth thinking about; for example, the Maxine JVM implementation has a hybrid object/array type.  Something like this which can also accommodate value type components seems worthwhile.  On the other hand, does it make sense for value types to contain short arrays?  And why should random-access arrays be the end of our design process, when bulk data is often sequentially accessed, and it might make sense to have heterogeneous streams of data as the natural “jumbo” data structure.  These considerations must wait for another day and another note. More Work It seems to me that a good sequence for introducing such value types would be as follows: Add the value-safety restrictions to an experimental version of javac. Code some sample applications with value types, including Complex and DecimalValue. Create an experimental JVM which internally unboxes value types but does not require new bytecodes to do so.  Ensure the feasibility of the performance model for the sample applications. Add tuple-like bytecodes (with or without generic type reification) to a major revision of the JVM, and teach the Java compiler to switch in the new bytecodes without code changes. A staggered roll-out like this would decouple language changes from bytecode changes, which is always a convenient thing. A similar investigation should be applied (concurrently) to array types.  In this case, it seems to me that the starting point is in the JVM: Add an experimental unboxing array data structure to a production JVM, perhaps along the lines of Maxine hybrids.  No bytecode or language support is required at first; everything can be done with encapsulated unsafe operations and/or method handles. Create an experimental JVM which internally unboxes value types but does not require new bytecodes to do so.  Ensure the feasibility of the performance model for the sample applications. Add tuple-like bytecodes (with or without generic type reification) to a major revision of the JVM, and teach the Java compiler to switch in the new bytecodes without code changes. That’s enough musing me for now.  Back to work!

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  • Sharp architecture; Accessing Validation Results

    - by nabeelfarid
    I am exploring Sharp Architecture and I would like to know how to access the validation results after calling Entity.IsValid(). I have two scenarios e.g. 1) If the entity.IsValid() return false, I would like to add the errors to ModelState.AddModelError() collection in my controller. E.g. in the Northwind sample we have an EmployeesController.Create() action when we do employee.IsValid(), how can I get access to the errors? public ActionResult Create(Employee employee) { if (ViewData.ModelState.IsValid && employee.IsValid()) { employeeRepository.SaveOrUpdate(employee); } // .... } [I already know that when an Action method is called, modelbinder enforces validation rules(nhibernate validator attributes) as it parses incoming values and tries to assign them to the model object and if it can't parse the incoming values  then it register those as errors in modelstate for each model object property. But what if i have some custom validation. Thats why we do ModelState.IsValid first.] 2) In my test methods I would like to test the nhibernate validation rules as well. I can do entity.IsValid() but that only returns true/ false. I would like to Assert against the actual error not just true/ false. In my previous projects, I normally use a wrapper Service Layer for Repositories, and instead of calling Repositories method directly from controller, controllers call service layer methods which in turn call repository methods. In my Service Layer all my custom validation rules resides and Service Layer methods throws a custom exception with a NameValueCollection of errors which I can easily add to ModelState in my controller. This way I can also easily implement sophisticated business rules in my service layer as well. I kow sharp architecture also provides a Service Layer project. But what I am interested in and my next question is: How I can use NHibernate Vaidators to implement sophisticated custom business rules (not just null,empty, range etc.) and make Entity.IsValid() to verify those rules too ?

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  • How to approach ninject container/kernel in inheritance situation

    - by Bas
    I have the following situation: class RuleEngine {} abstract class RuleImplementation {} class RootRule : RuleImplementation {} class Rule1 : RuleImplementation {} class Rule2 : RuleImplementation {} The RuleEngine is injected by Ninject and has a kernel at it's disposal, the role of the RuleEngine is to fire off the root rule, which on it's turn will load all the other rules also using Ninject, but using a different Module and creating a new Kernel. Now my question is, some of the rules require some dependencies which I want to inject using Ninject. What would be the best way to create the kernel for these rules and also still do proper unit testing with it? (the kernel shouldn't become a real pain in my tests) I've been thinking of the following possibilitys: The kernel that I use in the RuleEngine class could be tossed around to RuleImplementation and thus be available for every rule. But tossing around Kernels isn't really something I wish to do. When creating the rules, I could give the kernel (which creates the rules) as a constructor argument for each rule. I could create a method inside the RuleImplementation which creates a kernel and makes it possible for the rules to retrieve the kernel using a get() in the abstract class Whats the convention of passing around/creating kernels? Just create new kernels, or reuse them?

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  • Why linking doesn't work in my Xtext-based DSL?

    - by reprogrammer
    The following is the Xtext grammar for my DSL. Model: variableTypes=VariableTypes predicateTypes=PredicateTypes variableDeclarations= VariableDeclarations rules=Rules; VariableType: name=ID; VariableTypes: 'var types' (variableTypes+=VariableType)+; PredicateTypes: 'predicate types' (predicateTypes+=PredicateType)+; PredicateType: name=ID '(' (variableTypes+=[VariableType|ID])+ ')'; VariableDeclarations: 'vars' (variableDeclarations+=VariableDeclaration)+; VariableDeclaration: name=ID ':' type=[VariableType|ID]; Rules: 'rules' (rules+=Rule)+; Rule: head=Head ':-' body=Body; Head: predicate=Predicate; Body: (predicates+=Predicate)+; Predicate: predicateType=[PredicateType|ID] '(' (terms+=Term)+ ')'; Term: variable=Variable; Variable: variableDeclaration=[VariableDeclaration|ID]; terminal WS: (' ' | '\t' | '\r' | '\n' | ',')+; And, the following is a program in the above DSL. var types Node predicate types Edge(Node, Node) Path(Node, Node) vars x : Node y : Node z : Node rules Path(x, y) :- Edge(x, y) Path(x, y) :- Path(x, z) Path(z, y) When I used the generated Switch class to traverse the EMF object model corresponding to the above program, I realized that the nodes are not linked together properly. For example, the getPredicateType() method on a Predicate node returns null. Having read the Xtext user's guide, my impression is that the Xtext default linking semantics should work for my DSL. But, for some reason, the AST nodes of my DSL don't get linked together properly. Can anyone help me in diagnosing this problem?

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  • Data Auditor by Example

    - by Jinjin.Wang
    OWB has a node Data Auditors under Oracle Module in Projects Navigator. What is data auditor and how to use it? I will give an introduction to data auditor and show its usage by examples. Data auditor is an important tool in ensuring that data quality levels meet business requirements. Data auditor validates data against a set of data rules to determine which records comply and which do not. It gathers statistical metrics on how well the data in a system complies with a rule by auditing and marking how many errors are occurring against the audited table. Data auditors are typically scheduled for regular execution as part of a process flow, to monitor the quality of the data in an operational environment such as a data warehouse or ERP system, either immediately after updates like data loads, or at regular intervals. How to use data auditor to monitor data quality? Only objects with data rules can be monitored, so the first step is to define data rules according to business requirements and apply them to the objects you want to monitor. The objects can be tables, views, materialized views, and external tables. Secondly create a data auditor containing the objects. You can configure the data auditor and set physical deployment parameters for it as optional, which will be used while running the data auditor. Then deploy and run the data auditor either manually or as part of the process flow. After execution, the data auditor sets several output values, and records that are identified as not complying with the defined data rules contained in the data auditor are written to error tables. Here is an example. We have two tables DEPARTMENTS and EMPLOYEES (see pic-1 and pic-2. Click here for DDL and data) imported into OWB. We want to gather statistical metrics on how well data in these two tables satisfies the following requirements: a. Values of the EMPLOYEES.EMPLOYEE_ID attribute are three-digit numbers. b. Valid values for EMPLOYEES.JOB_ID are IT_PROG, SA_REP, SH_CLERK, PU_CLERK, and ST_CLERK. c. EMPLOYEES.EMPLOYEE_ID is related to DEPARTMENTS.MANAGER_ID. Pic-1 EMPLOYEES Pic-2 DEPARTMENTS 1. To determine legal data within EMPLOYEES or legal relationships between data in different columns of the two tables, firstly we define data rules based on the three requirements and apply them to tables. a. The first requirement is about patterns that an attribute is allowed to conform to. We create a Domain Pattern List data rule EMPLOYEE_PATTERN_RULE here. The pattern is defined in the Oracle Database regular expression syntax as ^([0-9]{3})$ Apply data rule EMPLOYEE_PATTERN_RULE to table EMPLOYEES.

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  • URL Rewrite – Protocol (http/https) in the Action

    - by OWScott
    IIS URL Rewrite supports server variables for pretty much every part of the URL and http header. However, there is one commonly used server variable that isn’t readily available.  That’s the protocol—HTTP or HTTPS. You can easily check if a page request uses HTTP or HTTPS, but that only works in the conditions part of the rule.  There isn’t a variable available to dynamically set the protocol in the action part of the rule.  What I wish is that there would be a variable like {HTTP_PROTOCOL} which would have a value of ‘HTTP’ or ‘HTTPS’.  There is a server variable called {HTTPS}, but the values of ‘on’ and ‘off’ aren’t practical in the action.  You can also use {SERVER_PORT} or {SERVER_PORT_SECURE}, but again, they aren’t useful in the action. Let me illustrate.  The following rule will redirect traffic for http(s)://localtest.me/ to http://www.localtest.me/. <rule name="Redirect to www"> <match url="(.*)" /> <conditions> <add input="{HTTP_HOST}" pattern="^localtest\.me$" /> </conditions> <action type="Redirect" url="http://www.localtest.me/{R:1}" /> </rule> The problem is that it forces the request to HTTP even if the original request was for HTTPS. Interestingly enough, I planned to blog about this topic this week when I noticed in my twitter feed yesterday that Jeff Graves, a former colleague of mine, just wrote an excellent blog post about this very topic.  He beat me to the punch by just a couple days.  However, I figured I would still write my blog post on this topic.  While his solution is a excellent one, I personally handle this another way most of the time.  Plus, it’s a commonly asked question that isn’t documented well enough on the web yet, so having another article on the web won’t hurt. I can think of four different ways to handle this, and depending on your situation you may lean towards any of the four.  Don’t let the choices overwhelm you though.  Let’s keep it simple, Option 1 is what I use most of the time, Option 2 is what Jeff proposed and is the safest option, and Option 3 and Option 4 need only be considered if you have a more unique situation.  All four options will work for most situations. Option 1 – CACHE_URL, single rule There is a server variable that has the protocol in it; {CACHE_URL}.  This server variable contains the entire URL string (e.g. http://www.localtest.me:80/info.aspx?id=5)  All we need to do is extract the HTTP or HTTPS and we’ll be set. This tends to be my preferred way to handle this situation. Indeed, Jeff did briefly mention this in his blog post: … you could use a condition on the CACHE_URL variable and a back reference in the rewritten URL. The problem there is that you then need to match all of the conditions which could be a problem if your rule depends on a logical “or” match for conditions. Thus the problem.  If you have multiple conditions set to “Match Any” rather than “Match All” then this option won’t work.  However, I find that 95% of all rules that I write use “Match All” and therefore, being the lazy administrator that I am I like this simple solution that only requires adding a single condition to a rule.  The caveat is that if you use “Match Any” then you must consider one of the next two options. Enough with the preamble.  Here’s how it works.  Add a condition that checks for {CACHE_URL} with a pattern of “^(.+)://” like so: How you have a back-reference to the part before the ://, which is our treasured HTTP or HTTPS.  In URL Rewrite 2.0 or greater you can check the “Track capture groups across conditions”, make that condition the first condition, and you have yourself a back-reference of {C:1}. The “Redirect to www” example with support for maintaining the protocol, will become: <rule name="Redirect to www" stopProcessing="true"> <match url="(.*)" /> <conditions trackAllCaptures="true"> <add input="{CACHE_URL}" pattern="^(.+)://" /> <add input="{HTTP_HOST}" pattern="^localtest\.me$" /> </conditions> <action type="Redirect" url="{C:1}://www.localtest.me/{R:1}" /> </rule> It’s not as easy as it would be if Microsoft gave us a built-in {HTTP_PROTOCOL} variable, but it’s pretty close. I also like this option since I often create rule examples for other people and this type of rule is portable since it’s self-contained within a single rule. Option 2 – Using a Rewrite Map For a safer rule that works for both “Match Any” and “Match All” situations, you can use the Rewrite Map solution that Jeff proposed.  It’s a perfectly good solution with the only drawback being the ever so slight extra effort to set it up since you need to create a rewrite map before you create the rule.  In other words, if you choose to use this as your sole method of handling the protocol, you’ll be safe. After you create a Rewrite Map called MapProtocol, you can use “{MapProtocol:{HTTPS}}” for the protocol within any rule action.  Following is an example using a Rewrite Map. <rewrite> <rules> <rule name="Redirect to www" stopProcessing="true"> <match url="(.*)" /> <conditions trackAllCaptures="false"> <add input="{HTTP_HOST}" pattern="^localtest\.me$" /> </conditions> <action type="Redirect" url="{MapProtocol:{HTTPS}}://www.localtest.me/{R:1}" /> </rule> </rules> <rewriteMaps> <rewriteMap name="MapProtocol"> <add key="on" value="https" /> <add key="off" value="http" /> </rewriteMap> </rewriteMaps> </rewrite> Option 3 – CACHE_URL, Multi-rule If you have many rules that will use the protocol, you can create your own server variable which can be used in subsequent rules. This option is no easier to set up than Option 2 above, but you can use it if you prefer the easier to remember syntax of {HTTP_PROTOCOL} vs. {MapProtocol:{HTTPS}}. The potential issue with this rule is that if you don’t have access to the server level (e.g. in a shared environment) then you cannot set server variables without permission. First, create a rule and place it at the top of the set of rules.  You can create this at the server, site or subfolder level.  However, if you create it at the site or subfolder level then the HTTP_PROTOCOL server variable needs to be approved at the server level.  This can be achieved in IIS Manager by navigating to URL Rewrite at the server level, clicking on “View Server Variables” from the Actions pane, and added HTTP_PROTOCOL. If you create the rule at the server level then this step is not necessary.  Following is an example of the first rule to create the HTTP_PROTOCOL and then a rule that uses it.  The Create HTTP_PROTOCOL rule only needs to be created once on the server. <rule name="Create HTTP_PROTOCOL"> <match url=".*" /> <conditions logicalGrouping="MatchAll" trackAllCaptures="false"> <add input="{CACHE_URL}" pattern="^(.+)://" /> </conditions> <serverVariables> <set name="HTTP_PROTOCOL" value="{C:1}" /> </serverVariables> <action type="None" /> </rule>   <rule name="Redirect to www" stopProcessing="true"> <match url="(.*)" /> <conditions logicalGrouping="MatchAll" trackAllCaptures="false"> <add input="{HTTP_HOST}" pattern="^localtest\.me$" /> </conditions> <action type="Redirect" url="{HTTP_PROTOCOL}://www.localtest.me/{R:1}" /> </rule> Option 4 – Multi-rule Just to be complete I’ll include an example of how to achieve the same thing with multiple rules. I don’t see any reason to use it over the previous examples, but I’ll include an example anyway.  Note that it will only work with the “Match All” setting for the conditions. <rule name="Redirect to www - http" stopProcessing="true"> <match url="(.*)" /> <conditions logicalGrouping="MatchAll" trackAllCaptures="false"> <add input="{HTTP_HOST}" pattern="^localtest\.me$" /> <add input="{HTTPS}" pattern="off" /> </conditions> <action type="Redirect" url="http://www.localtest.me/{R:1}" /> </rule> <rule name="Redirect to www - https" stopProcessing="true"> <match url="(.*)" /> <conditions logicalGrouping="MatchAll" trackAllCaptures="false"> <add input="{HTTP_HOST}" pattern="^localtest\.me$" /> <add input="{HTTPS}" pattern="on" /> </conditions> <action type="Redirect" url="https://www.localtest.me/{R:1}" /> </rule> Conclusion Above are four working examples of methods to call the protocol (HTTP or HTTPS) from the action of a URL Rewrite rule.  You can use whichever method you most prefer.  I’ve listed them in the order that I favor them, although I could see some people preferring Option 2 as their first choice.  In any of the cases, hopefully you can use this as a reference for when you need to use the protocol in the rule’s action when writing your URL Rewrite rules. Further information: Viewing all Server Variable for a site. URL Parts available to URL Rewrite Rules Further URL Rewrite articles

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  • Domain Validation in a CQRS architecture

    - by Jupaol
    Basically I want to know if there is a better way to validate my domain entities. This is how I am planning to do it but I would like your opinion The first approach I considered was: class Customer : EntityBase<Customer> { public void ChangeEmail(string email) { if(string.IsNullOrWhitespace(email)) throw new DomainException(“...”); if(!email.IsEmail()) throw new DomainException(); if(email.Contains(“@mailinator.com”)) throw new DomainException(); } } I actually do not like this validation because even when I am encapsulating the validation logic in the correct entity, this is violating the Open/Close principle (Open for extension but Close for modification) and I have found that violating this principle, code maintenance becomes a real pain when the application grows up in complexity. Why? Because domain rules change more often than we would like to admit, and if the rules are hidden and embedded in an entity like this, they are hard to test, hard to read, hard to maintain but the real reason why I do not like this approach is: if the validation rules change, I have to come and edit my domain entity. This has been a really simple example but in RL the validation could be more complex So following the philosophy of Udi Dahan, making roles explicit, and the recommendation from Eric Evans in the blue book, the next try was to implement the specification pattern, something like this class EmailDomainIsAllowedSpecification : IDomainSpecification<Customer> { private INotAllowedEmailDomainsResolver invalidEmailDomainsResolver; public bool IsSatisfiedBy(Customer customer) { return !this.invalidEmailDomainsResolver.GetInvalidEmailDomains().Contains(customer.Email); } } But then I realize that in order to follow this approach I had to mutate my entities first in order to pass the value being valdiated, in this case the email, but mutating them would cause my domain events being fired which I wouldn’t like to happen until the new email is valid So after considering these approaches, I came out with this one, since I am going to implement a CQRS architecture: class EmailDomainIsAllowedValidator : IDomainInvariantValidator<Customer, ChangeEmailCommand> { public void IsValid(Customer entity, ChangeEmailCommand command) { if(!command.Email.HasValidDomain()) throw new DomainException(“...”); } } Well that’s the main idea, the entity is passed to the validator in case we need some value from the entity to perform the validation, the command contains the data coming from the user and since the validators are considered injectable objects they could have external dependencies injected if the validation requires it. Now the dilemma, I am happy with a design like this because my validation is encapsulated in individual objects which brings many advantages: easy unit test, easy to maintain, domain invariants are explicitly expressed using the Ubiquitous Language, easy to extend, validation logic is centralized and validators can be used together to enforce complex domain rules. And even when I know I am placing the validation of my entities outside of them (You could argue a code smell - Anemic Domain) but I think the trade-off is acceptable But there is one thing that I have not figured out how to implement it in a clean way. How should I use this components... Since they will be injected, they won’t fit naturally inside my domain entities, so basically I see two options: Pass the validators to each method of my entity Validate my objects externally (from the command handler) I am not happy with the option 1 so I would explain how I would do it with the option 2 class ChangeEmailCommandHandler : ICommandHandler<ChangeEmailCommand> { public void Execute(ChangeEmailCommand command) { private IEnumerable<IDomainInvariantValidator> validators; // here I would get the validators required for this command injected, and in here I would validate them, something like this using (var t = this.unitOfWork.BeginTransaction()) { var customer = this.unitOfWork.Get<Customer>(command.CustomerId); this.validators.ForEach(x =. x.IsValid(customer, command)); // here I know the command is valid // the call to ChangeEmail will fire domain events as needed customer.ChangeEmail(command.Email); t.Commit(); } } } Well this is it. Can you give me your thoughts about this or share your experiences with Domain entities validation EDIT I think it is not clear from my question, but the real problem is: Hiding the domain rules has serious implications in the future maintainability of the application, and also domain rules change often during the life-cycle of the app. Hence implementing them with this in mind would let us extend them easily. Now imagine in the future a rules engine is implemented, if the rules are encapsulated outside of the domain entities, this change would be easier to implement

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  • Windows 2008 R2 IPsec encryption in tunnel mode, hosts in same subnet

    - by fission
    In Windows there appear to be two ways to set up IPsec: The IP Security Policy Management MMC snap-in (part of secpol.msc, introduced in Windows 2000). The Windows Firewall with Advanced Security MMC snap-in (wf.msc, introduced in Windows 2008/Vista). My question concerns #2 – I already figured out what I need to know for #1. (But I want to use the ‘new’ snap-in for its improved encryption capabilities.) I have two Windows Server 2008 R2 computers in the same domain (domain members), on the same subnet: server2 172.16.11.20 server3 172.16.11.30 My goal is to encrypt all communication between these two machines using IPsec in tunnel mode, so that the protocol stack is: IP ESP IP …etc. First, on each computer, I created a Connection Security Rule: Endpoint 1: (local IP address), eg 172.16.11.20 for server2 Endpoint 2: (remote IP address), eg 172.16.11.30 Protocol: Any Authentication: Require inbound and outbound, Computer (Kerberos V5) IPsec tunnel: Exempt IPsec protected connections Local tunnel endpoint: Any Remote tunnel endpoint: (remote IP address), eg 172.16.11.30 At this point, I can ping each machine, and Wireshark shows me the protocol stack; however, nothing is encrypted (which is expected at this point). I know that it's unencrypted because Wireshark can decode it (using the setting Attempt to detect/decode NULL encrypted ESP payloads) and the Monitor Security Associations Quick Mode display shows ESP Encryption: None. Then on each server, I created Inbound and Outbound Rules: Protocol: Any Local IP addresses: (local IP address), eg 172.16.11.20 Remote IP addresses: (remote IP address), eg 172.16.11.30 Action: Allow the connection if it is secure Require the connections to be encrypted The problem: Though I create the Inbound and Outbound Rules on each server to enable encryption, the data is still going over the wire (wrapped in ESP) with NULL encryption. (You can see this in Wireshark.) When the arrives at the receiving end, it's rejected (presumably because it's unencrypted). [And, disabling the Inbound rule on the receiving end causes it to lock up and/or bluescreen – fun!] The Windows Firewall log says, eg: 2014-05-30 22:26:28 DROP ICMP 172.16.11.20 172.16.11.30 - - 60 - - - - 8 0 - RECEIVE I've tried varying a few things: In the Rules, setting the local IP address to Any Toggling the Exempt IPsec protected connections setting Disabling rules (eg disabling one or both sets of Inbound or Outbound rules) Changing the protocol (eg to just TCP) But realistically there aren't that many knobs to turn. Does anyone have any ideas? Has anyone tried to set up tunnel mode between two hosts using Windows Firewall? I've successfully got it set up in transport mode (ie no tunnel) using exactly the same set of rules, so I'm a bit surprised that it didn't Just Work™ with the tunnel added.

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  • Javascript on a desktop wallpaper (XP)

    - by Arcath
    I have a desktop wallpaper shipped out by my domain, it's a HTML wallpaper that displays information like today's date, etc. It also has the internet usage rules. Using jquery I've made it so that the rules are hidden and displayed when you click on the section heading. The JS runs fine and it hides the rules, but it appears that once the desktop "loses focus" the javascript stops and clicking the headings does nothing. Anyone know a way to keep javascript running?

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  • F5 BIG_IP persistence iRules applied but not affecting selected member

    - by zoli
    I have a virtual server. I have 2 iRules (see below) assigned to it as resources. From the server log it looks like that the rules are running and they select the correct member from the pool after persisting the session (as far as I can tell based on my log messages), but the requests are ultimately directed to somewhere else. Here's how both rules look like: when HTTP_RESPONSE { set sessionId [HTTP::header X-SessionId] if {$sessionId ne ""} { persist add uie $sessionId 3600 log local0.debug "Session persisted: <$sessionId> to <[persist lookup uie $sessionId]>" } } when HTTP_REQUEST { set sessionId [findstr [HTTP::path] "/session/" 9 /] if {$sessionId ne ""} { persist uie $sessionId set persistValue [persist lookup uie $sessionId] log local0.debug "Found persistence key <$sessionId> : <$persistValue>" } } According to the log messages from the rules, the proper balancer members are selected. Note: the two rules can not conflict, they are looking for different things in the path. Those two things never appear in the same path. Notes about the server: * The default load balancing method is RR. * There is no persistence profile assigned to the virtual server. I'm wondering if this should be adequate to enable the persistence, or alternatively, do I have to combine the 2 rules and create a persistence profile with them for the virtual server? Or is there something else that I have missed?

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  • Linux service --status-all shows "Firewall is stopped." what service does firewall refer to?

    - by codewaggle
    I have a development server with the lamp stack running CentOS: [Prompt]# cat /etc/redhat-release CentOS release 5.8 (Final) [Prompt]# cat /proc/version Linux version 2.6.18-308.16.1.el5xen ([email protected]) (gcc version 4.1.2 20080704 (Red Hat 4.1.2-52)) #1 SMP Tue Oct 2 22:50:05 EDT 2012 [Prompt]# yum info iptables Loaded plugins: fastestmirror Loading mirror speeds from cached hostfile * base: mirror.anl.gov * extras: centos.mirrors.tds.net * rpmfusion-free-updates: mirror.us.leaseweb.net * rpmfusion-nonfree-updates: mirror.us.leaseweb.net * updates: mirror.steadfast.net Installed Packages Name : iptables Arch : x86_64 Version : 1.3.5 Release : 9.1.el5 Size : 661 k Repo : installed .... Snip.... When I run: service --status-all Part of the output looks like this: .... Snip.... httpd (pid xxxxx) is running... Firewall is stopped. Table: filter Chain INPUT (policy DROP) num target prot opt source destination 1 RH-Firewall-1-INPUT all -- 0.0.0.0/0 0.0.0.0/0 Chain FORWARD (policy DROP) num target prot opt source destination 1 RH-Firewall-1-INPUT all -- 0.0.0.0/0 0.0.0.0/0 Chain OUTPUT (policy ACCEPT) num target prot opt source destination Chain RH-Firewall-1-INPUT (2 references) ....Snip.... iptables has been loaded to the kernel and is active as represented by the rules being displayed. Checking just the iptables returns the rules just like status all does: [Prompt]# service iptables status Table: filter Chain INPUT (policy DROP) num target prot opt source destination 1 RH-Firewall-1-INPUT all -- 0.0.0.0/0 0.0.0.0/0 Chain FORWARD (policy DROP) num target prot opt source destination 1 RH-Firewall-1-INPUT all -- 0.0.0.0/0 0.0.0.0/0 Chain OUTPUT (policy ACCEPT) num target prot opt source destination Chain RH-Firewall-1-INPUT (2 references) .... Snip.... Starting or restarting iptables indicates that the iptables have been loaded to the kernel successfully: [Prompt]# service iptables restart Flushing firewall rules: [ OK ] Setting chains to policy ACCEPT: filter [ OK ] Unloading iptables modules: [ OK ] Applying iptables firewall rules: [ OK ] Loading additional iptables modules: ip_conntrack_netbios_n[ OK ] [Prompt]# service iptables start Flushing firewall rules: [ OK ] Setting chains to policy ACCEPT: filter [ OK ] Unloading iptables modules: [ OK ] Applying iptables firewall rules: [ OK ] Loading additional iptables modules: ip_conntrack_netbios_n[ OK ] I've googled "Firewall is stopped." and read a number of iptables guides as well as the RHEL documentation, but no luck. As far as I can tell, there isn't a "Firewall" service, so what is the line "Firewall is stopped." referring to?

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  • .htaccess redirect, from old dirty URL to a clean new URL with parameters

    - by JustAnil
    I have the following 2 links, I'm not great with .htaccess rules yet. Old URL: http://www.mywebsite.org.uk/donate/donate.php?charity_id=885&project_id=18111 New URL: http://new.mywebsite.org.uk/donation/to/885/18111 I want all the traffic coming from the old URL to the new url (including the parameters charity_id & project_id). I'm trying to learn .htaccess rules, but finding the tutorials online to be kinda vague. I'd really like a simple explanation on the .htaccess rules. (Give a man a fish, feed him for a day, teach a man to fish, feed him for a lifetime). The correct answer will be the answer with a simple and useful explanation (along with the rules if possible!).

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  • iptables blank after reboot

    - by theillien
    We've started encountering an issue with iptables on our RHEL 6.3 systems in that after a reboot, when the service starts, the rules are not loaded. We get the empty ruleset: [msnyder@matt-test ~]$ sudo iptables -L Chain INPUT (policy ACCEPT) target prot opt source destination Chain FORWARD (policy ACCEPT) target prot opt source destination Chain OUTPUT (policy ACCEPT) target prot opt source destination This is in spite of the fact that we have rules defined and the service is, indeed, running. That I know because when I run service iptables start it simply drops back to the prompt. If I run service iptables restart it actually stops and then restarts the service. And, of course, if I run service iptables stop it indicates that iptables is actually stopping. Knowing that I need to restart the service, I do so and the rules load up properly. They simply don't get loaded after a reboot. Unless they get loaded differently during a reboot I don't see how our rules would be wrong. If they were, they wouldn't even load during a service restart. Has anyone else ever encountered this? EDIT: The rules are already saved in /etc/sysconfig/iptables. They are not added on the fly from the command line so service iptables save is unnecessary.

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  • How do I set up pairing email addresses?

    - by James A. Rosen
    Our team uses the Ruby gem hitch to manage pairing. You set it up with a group email address (e.g. [email protected]) and then tell it who is pairing: $ hitch james tiffany Hitch then sets your Git author configuration so that our commits look like commit 629dbd4739eaa91a720dd432c7a8e6e1a511cb2d Author: James and Tiffany <[email protected]> Date: Thu Oct 31 13:59:05 2013 -0700 Unfortunately, we've only been able to come up with two options: [email protected] doesn't exist. The downside is that if Travis CI tries to notify us that we broke the build, we don't see it. [email protected] does exist and forwards to all the developers. Now the downside is that everyone gets spammed with every broken build by every pair. We have too many possible pair to do any of the following: set up actual [email protected] email addresses or groups (n^2 email addresses) set up forwarding rules for [email protected] (n^2 forwarding rules) set up forwarding rules for [email protected] (n forwarding rules for each of n developers) Does anyone have a system that works for them?

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  • Adding dynamic business logic/business process checks to a system

    - by Jordan Reiter
    I'm wondering if there is a good extant pattern (language here is Python/Django but also interested on the more abstract level) for creating a business logic layer that can be created without coding. For example, suppose that a house rental should only be available during a specific time. A coder might create the following class: from bizlogic import rules, LogicRule from orders.models import Order class BeachHouseAvailable(LogicRule): def check(self, reservation): house = reservation.house_reserved if not (house.earliest_available < reservation.starts < house.latest_available ) raise RuleViolationWhen("Beach house is available only between %s and %s" % (house.earliest_available, house.latest_available)) return True rules.add(Order, BeachHouseAvailable, name="BeachHouse Available") This is fine, but I don't want to have to code something like this each time a new rule is needed. I'd like to create something dynamic, ideally something that can be stored in a database. The thing is, it would have to be flexible enough to encompass a wide variety of rules: avoiding duplicates/overlaps (to continue the example "You already have a reservation for this time/location") logic rules ("You can't rent a house to yourself", "This house is in a different place from your chosen destination") sanity tests ("You've set a rental price that's 10x the normal rate. Are you sure this is the right price?" Things like that. Before I recreate the wheel, I'm wondering if there are already methods out there for doing something like this.

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  • Formalizing a requirements spec written in narrative English

    - by ProfK
    I have a fairly technical functionality requirements spec, expressed in English prose, produced by my project manager. It is structured as a collection of UI tabs, where the requirements for each tab are expressed as a lit of UI fields and a list of business rules for the tab. Most business rules are for UI fields on a tab, e.g: a) Must be alphanumeric, max length 20. b) Must be a dropdown, with values from table x. c) Is mandatory. d) Is mandatory under certain conditions, e.g. another field is just populated, or has a specific value. Then other business rules get a little more complex. The spec is for a job application, so the central business object (table) is the Applicant, and we have several other tables with one-to-many relationships with applicant, such as Degree, HighSchool, PreviousEmployer, Diploma, etc. e) One such complex rule says a status field can only be assigned a certain value if a many-side record exists in at least one of the many-side tables. E.g. the Applicant has at least one HighSchool or at least one Diploma record. I am looking for advice on how to codify these requirements into a more structured specification defined in terms of tables, fields, and relationships, especially for the conditional rules for fields and for the presence of related records. Any suggestions and advice will be most welcome, but I would be overjoyed if i could find an already defined system or structure for expressing things like this.

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  • Codifying a natural language requirements spec

    - by ProfK
    I have a fairly technical functionality requirements spec, expressed in English prose, produced by my project manager. It is structured as a collection of UI tabs, where the requirements for each tab are expressed as a lit of UI fields and a list of business rules for the tab. Most business rules are for UI fields on a tab, e.g: a) Must be alphanumeric, max length 20. b) Must be a dropdown, with values from table x. c) Is mandatory. d) Is mandatory under certain conditions, e.g. another field is just populated, or has a specific value. Then other business rules get a little more complex. The spec is for a job application, so the central business object (table) is the Applicant, and we have several other tables with one-to-many relationships with applicant, such as Degree, HighSchool, PreviousEmployer, Diploma, etc. e) One such complex rule says a status field can only be assigned a certain value if a many-side record exists in at least one of the many-side tables. E.g. the Applicant has at least one HighSchool or at least one Diploma record. I am looking for advice on how to codify these requirements into a more structured specification defined in terms of tables, fields, and relationships, especially for the conditional rules for fields and for the presence of related records. Any suggestions and advice will be most welcome, but I would be overjoyed if i could find an already defined system or structure for expressing things like this.

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