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  • How to use a nested form for multiple models in one form?

    - by Magicked
    I'm struggling to come up with the proper way to design a form that will allow me to input data for two different models. The form is for an 'Incident', which has the following relationships: belongs_to :customer belongs_to :user has_one :incident_status has_many :incident_notes accepts_nested_attributes_for :incident_notes, :allow_destroy => false So an incident is assigned to a 'Customer' and a 'User', and the user is able to add 'Notes' to the incident. I'm having trouble with the notes part of the form. Here how the form is being submitted: {"commit"=>"Create", "authenticity_token"=>"ECH5Ziv7JAuzs53kt5m/njT9w39UJhfJEs2x0Ms2NA0=", "customer_id"=>"4", "incident"=>{"title"=>"Something bad", "incident_status_id"=>"2", "user_id"=>"2", "other_id"=>"AAA01-042310-001", "incident_note"=>{"note"=>"This is a note"}}} It appears to be attempting to add the incident_note as a field under 'Incident', rather than creating a new entry in the incident_note table with an incident_id foreign key linking back to the incident. Here is the 'IncidentNote' model: belongs_to :incident belongs_to :user Here is the form for 'Incident': <% form_for([@customer,@incident]) do |f| %> <%= f.error_messages %> <p> <%= f.label :other_id, "ID" %><br /> <%= f.text_field :capc_id %> </p> <p> <%= f.label :title %><br /> <%= f.text_field :title %> </p> <p> <%= label_tag 'user', 'Assign to user?' %> <%= f.select :user_id, @users.collect {|u| [u.name, u.id]} %> </p> <p> <%= f.label :incident_status, 'Status?' %> <%= f.select :incident_status_id, @statuses.collect {|s| [s.name, s.id]} %> </p> <p> <% f.fields_for :incident_note do |inote_form| %> <%= inote_form.label :note, 'Add a Note' %> <%= inote_form.text_area :note, :cols => 40, :rows => 20 %> <% end %> </p> <p> <%= f.submit "Create" %> </p> <% end %> And finally, here are the incident_controller entries for New and Create. New: def new @customer = current_user.customer @incident = Incident.new @users = @customer.users @statuses = IncidentStatus.find(:all) @incident_note = IncidentNote.new respond_to do |format| format.html # new.html.erb format.xml { render :xml => @incident } end end Create: def create @users = @customer.users @statuses = IncidentStatus.find(:all) @incident = Incident.new(params[:incident]) @incident.customer = @customer @incident_note = @incident.incident_note.build(params[:incident_note]) @incident_note.user = current_user respond_to do |format| if @incident.save flash[:notice] = 'Incident was successfully created.' format.html { redirect_to(@incident) } format.xml { render :xml => @incident, :status => :created, :location => @incident } else format.html { render :action => "new" } format.xml { render :xml => @incident.errors, :status => :unprocessable_entity } end end end I'm not really sure where to look at this point. I'm sure it's just a limitation of my current Rails skill (I don't know much). So if anyone can point me in the right direction I would be very appreciative. Please let me know if more information is needed! Thanks!

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  • Windows "known folders": is there any one of them which is reliably read/write for all users on all

    - by Stabledog
    SHGetKnownFolderPath() and its cohorts accept one of the constants defined here (http://msdn.microsoft.com/en-us/library/dd378457%28v=VS.85%29.aspx ), returning the path to a directory. I'm looking for one of these folders which is reliably writable by all users (including LocalSystem) on XP, Vista, and Windows 7... but I think I'm striking out. It appears that, in fact, there is no single location on the hard drive anymore where you can put a file and be assured that all users can write to it on all these OS versions, without fiddling the permissions first. Is this true?

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  • Why do users have to enter a 7-digit twitter PIN to grant my application access?

    - by Tony
    I am implementing some ruby on rails code tweet stuff for my users. I am creating the proper oauth link...something like http://twitter.com/oauth/authorize?oauth_token=y2RkuftYAEkbEuIF7zKMuzWN30O2XxM8U9j0egtzKv But after my test account grants access to twitter, it pulls up a page saying "You've successfully granted access to . Simply return to and enter the following PIN to complete the process. 1234567" I have no idea where the user should enter this PIN and why they have to do that. I don't think this should be a necessary step. Twitter should be redirecting the user to the callback URL I provided in the application settings. Does anyone know why this is happening? UPDATE I found this article that states I need to send my users to this URL (note "authenticate" instead of "authorize"): http://twitter.com/oauth/authenticate?oauth_token=y2RkuftYAEkbEuIF7zKMuzWN30O2XxM8U9j0egtzKv I made the change but Twitter redirects the user to the authorize path after he clicks "Allow" which then gives him the 7 digit PIN again!

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  • How should I go about creating a point system for users like SO and yahoo answers?(PHP)

    - by ggfan
    I am creating a voting system for a Q&A site project in which if a user asks a question, he/she losses -5 points; answer a question +5, vote a question +1, etc. (kind of like SO and yahoo answers) --To create the basic arithmetic, I have a "users_points" table that relates the user_id and their total points. +---+---------+ | 1 | 100 | +---+---------+ | 2 | 54 | +---+---------+ --Basically if the users does certain task, it would + or - the points. How do I prevent users from say voting an answer up 100 times. ex: I want a user to be only able to vote once per question, etc.

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  • Alternatives to requiring users to register for an account?

    - by jamieb
    I'm working on a side project to build a new web app idea of mine. For the sake of discussion, let's say this app displays a random photograph of a famous work of art. On a scale of 1 to 5, users are asked to rate how well they like each piece of art, and then are shown the next photo. Eventually, the app is able to get an sense of the person's style and is able to recommend artwork that he/she may find pleasing. The whole concept is similar to Netflix. I understand how to do all the preference matching logic (although not as sophisticated as Netflix). But I'd like to find a way to do this without requiring that users create an account first. This is a novelty website that a typical user might use only a handful of times. Requiring registration is overkill and will likely drastically reduce it's utility. I'd like to allow people to begin rating artwork within five seconds of their initial pageview, yet maintain the integrity of the voting (since recommendations are predicated on how other people have rated the various pieces of artwork). Can it be done? Some ideas: OpenID. The perfect solution except for the fact that it's not wildly used and my target audience isn't the most technically adept demographic. Text message. User inputs phone number and is texted a four digit code to key into the web app. Quick, easy, and great way to limit abuse. However, privacy concerns abound... people are probably even less likely to give me their phone number than their email address. Facebook login. I personally don't have a Facebook account due to privacy concerns. And I'd really hate to support such a proprietary platform. Hash code/Bookmark. Vistor's initial pageview generates a 5 or 6 digit alphanumeric code that is embedded in each subsequent URL. They can bookmark any page to save their state. Good: Very simple system that doesn't require any user action. Bad: Very easy to stuff the ballot box, might be difficult to account for users sharing the link containing their ID code via email or social networking sites.

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  • Can you let users upload Sinatra apps and run them inside Rails as middleware?

    - by Brian Armstrong
    I want to let users write small custom apps (think themes or plugins on Wordpress) and upload/run them on my site. I'm thinking about using Sinatra apps for this since it would give the users a lot of flexibility, and then running them as middleware inside my rails app. But I can't figure out the security implications of this. I tried creating a simple sinatra app as middleware, and it has access to all the rails models and everything - so that is bad. Is there a way for rack to keep these separate so that the sinatra apps are effectively sandboxed and can't do any bad things (outside of an API or some specific way I setup for them to communicate)? There may be an easier way to accomplish this that I haven't thought of too, so ideas welcome. Thanks!

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  • How to send reminder emails based on users input time and day (based on their time zone)

    - by evgelen
    I need to send emails based on users input time and day (based on their time zone)? Kind of a reminder. For Example: User input 2:00pm Eastern Time on my server I have different time zone, how to calculate the time and send the email at users time-zone. Its a web application. What is the best way to accomplish it using asp.net c#? If somebody already done it in the past I will be glad to take a look at source code. Thank you for useful suggestions.

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  • Is it OK to allow users to query an OLTP SQL Server database with excel?

    - by user169867
    I have a SQL Server 2005 database used by several applications. Some users wish to query the database directly from excel. I can understand this, because it is a useful tool for adhoc queries and then getting the data in a format that's easily transmitted and manipulated by other users. My question is: Does Excel (say 2003/2007) do its querying in a way that won't cause concurency issues? Or is it done in such a way that a seperate datawarehouse database needs to be made to handle this scenario? Thanks for any advise.

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  • CPU Usage relative to number of users? - ASP.Net Application

    - by soldieraman
    My Asp.net application uses 25-30% of the CPU on a test server which has 600 MB Ram on it. I can see the asp_wb process taking that much percentage of CPU. This is when I am testing using one user. How many users can the server afford then without falling over? Is there a relationship between the CPU Usage and number of user aka if there are 2 users my application will sky rocket to 60% of memory usage? Or does/Should/How does the server handle this?

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  • I want to use facebook connect in my website to register, login and comment on news articles or posts made by other users

    - by sasi kiran
    I would like to implement the following things in my website. I have done some extensive search over the internet but couldnt find and specific examples on how to implement them I am developing this site in php using a mvc framework Would like to have facebook registration on my website - users who have an account in facebook will get an option to use the details to register in my site, using their authentication I would pull the relavant details from their account and create a new account for them in my website. I would like to use facebook register fbml/fbjs in this case Would like to have facebook login used to login into my site. How to use the sessions is what I would like to know? I would like to make posts to the facebook-wall of the users registered in my site. Also if possible sent messages to them through my code whenever a new post is made to my site. Thanks for your help.

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  • How to distribute iPhone application among 50 specific users?

    - by Miraaj
    Hi all, I am developing an iPhone application which I need to distribute to an organization of about approximately 50 people, no. of users can increase or decrease in future. I checked my iPhone developer account, there I got that I can distribute my application via Adhoc Distribution up to 100 iPhone or iPod touch users. So I think it should be best way to distribute my application to that XYZ organization. On further searching I found that there is also an - iPhone Developer Enterprise Program, which is available to companies with 500 or more employees and a Dun & Bradstreet number. So I want to know - which will be the best way for me according to my requirements ? Also I want to know that say if I choose Adhoc distribution then is there any way for automatic up-gradation in it ie. to install new version of my application on user's iPhone or iPod without deleting the old version. Thanks, Miraaj

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  • Can I use RVM to maintain a single version of Ruby for all users?

    - by Trevor Burnham
    I love RVM. I realize that the main use case for it is letting different users switch between different versions of Ruby. But let's say I'm deploying a Rails app to a server and I just want a single version of Ruby running. In particular, I want 1.9.2, which is a breeze to install with RVM but a pain without it. Is there a way that I can say "I want this to be the canonical Ruby installation for all users" (along with all of its gems) without having to create a bunch of symlinks by hand and change them every time I update to a newer Ruby release?

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  • Can SiteB Restrict Access Only to Users Authenticated on Site A? How?

    - by DaveDev
    I have recently been asked to estimate a piece of work which will provide functionality for authenticated users to access our site. The thing is, the user has to authenticate on a different site & domain to the one we are hosting. The user authenticates on SiteA.com and they are provided with a link to our site, SiteB. Only users who have authenticated on SiteA are allowed to access SiteB.com. I don't yet know what authentication system SiteA is using, but I thought I'd ask the community for some initial thoughts. Is this even possible? What do I need to consider? Thanks

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  • I need to send emails based on users input time and day (based on their time zone)? Kind of reminder

    - by evgelen
    I need to send emails based on users input time and day (based on their time zone)? Kind of reminder. For Example: User input 2:00pm Eastern Time on my server I have different time zone, how to calculate the time and send the email at users time-zone. Its a web application. What is the best way to accomplish it using asp.net c#? If somebody already done it in the past I will be glad to take a look at source code. Thank you for useful suggestions.

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  • How to edit files on the users file system from my web server?

    - by Abs
    Hello all, I am really looking for implementation advice as I have entered a new realm that I am not familiar with. At the simplest level, I would like to find a way that I can read/write to a users machine from my web server. For this to work, I think I will have to install some sort of "plugin" on the users machine which can receive (or poll?) the server for instructions. The above is the line of thought that I currently have, maybe using JAVA to do this. This needs to work on Linux, Mac and Windows OS. I am really looking for advice on the above, is it a good idea? Is there a better way of doing this? Is there something out there already that I can build on top of? I really appreciate all input and advice as this is something I have not done before. Thanks all

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  • How to distinguish between new and returning anonymous Drupal users?

    - by Matt V.
    Is there an easy way (or a module) in Drupal to distinguish between anonymous users who have never created an account versus those who are returning but are not currently logged in? For non-returning (ie, completely new) users, I'd like to have a front page that is very streamlined and focused on registration as the call-to-action. However, if someone is a returning user but not currently logged in, I'd like to present a lot more information on the front page and have login as the main call-to-action. I realize both pages would still need to have both login and register options available, I just want to make the focus significantly different between the two.

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  • How to configure multiple iSCSI Portal Groups on a EqualLogic PS6100?

    - by kce
    I am working on a migration from a VMware vSphere environment to a Hyper-V Cluster utilizing Windows Server 2012 R2. The setup is pretty small, an EqualLogic PS6100e and two Dell PowerConnect 5424 switches and handful of R710s and R620s. The SAN was configured as a non-RFC1918 network that is not assigned to our organization and since I am working on building a new virtualization environment I figured that this would be an appropriate time to do a subnet migration. I configured a separate VLAN and subnet on the switches and the two previously unused NICs on the PS6100's controllers. At this time I only have a single Hyper-V host cabled in but I can successfully ping the PS6100 from the host. From the PS6100 I can ping each of the four NICs that currently on the storage network. I cannot connect the Microsoft iSCSI Initiator to the Target. I have successfully added the Target Portals (the IP addresses of PS6100 NICs) and the Targets are discovered but listed as inactive. If I try to Connect to them I get the following error, "Log onto Target - Connection Failed" and ISCSIPrt 1 and 70 events are recorded in the Event Log. I have verified that access control to the volume is not the problem by temporarily disabling it. I suspect the problem is with the Portal Group IP address which is still listed as Group Address of old subnet (I know, I know I might be committing the sin of the X/Y problem but everything else looks good): RFC3720 has this to say about Network Portal and Portal Groups: Network Portal: The Network Portal is a component of a Network Entity that has a TCP/IP network address and that may be used by an iSCSI Node within that Network Entity for the connection(s) within one of its iSCSI sessions. A Network Portal in an initiator is identified by its IP address. A Network Portal in a target is identified by its IP address and its listening TCP port. Portal Groups: iSCSI supports multiple connections within the same session; some implementations will have the ability to combine connections in a session across multiple Network Portals. A Portal Group defines a set of Network Portals within an iSCSI Network Entity that collectively supports the capability of coordinating a session with connections spanning these portals. Not all Network Portals within a Portal Group need participate in every session connected through that Portal Group. One or more Portal Groups may provide access to an iSCSI Node. Each Network Portal, as utilized by a given iSCSI Node, belongs to exactly one portal group within that node. The EqualLogic Group Manager documentation has this to say about the Group IP Address: You use the group IP address as the iSCSI discovery address when connecting initiators to iSCSI targets in the group. If you modify the group IP address, you might need to change your initiator configuration to use the new discovery address Changing the group IP address disconnects any iSCSI connections to the group and any administrators logged in to the group through the group IP address. Which sounds equivalent to me (I am following up with support to confirm). I think a reasonable explanation at this point is that the Initiator can't complete the connection to the Target because the Group IP Address / Network Portal is on a different subnet. I really want to avoid a cutover and would prefer to run both subnets side-by-side until I can install and configure each Hyper-V host. Question/s: Is my assessment at all reasonable? Is it possible to configure multiple Group IP Addresses on the EqualLogic PS6100? I don't want to just change it as it will disconnect the remaining ESXi hosts. Am I just Doing It Wrong(TM)?

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  • Authenticate by libpam-mysql and libnss-mysql (CentOS)

    - by Chris
    I'm trying to get MySQL to function as a backend for authenticating users on CentOS 6.3. So far I have successfully installed and configured libnss-mysql. I can test this by doing: # groups testuser testuser : sftp Testuser is a member of the sftp group in fact, all MySQL based useraccounts will be hardcoded to it. The sftp group is chrooted and forced to use internal-sftp so they cannot do anything but access their home directory. Then I configured pam-mysql and PAM to allow mysql logins. This also works.. When SELinux is not enforcing. When I do setenforce 1 users can no longer login. Error: Permission denied, please try again. This is my pam_mysql.conf file: users.host=localhost users.db_user=nss-pam-user users.db_passwd=*********** users.database=sftpusers users.table=users users.user_column=username users.password_column=password users.password_crypt=6 verbose=1 My /etc/pam.d/sshd: #%PAM-1.0 auth sufficient pam_sepermit.so auth include password-auth auth required pam_mysql.so config_file=/etc/pam_mysql.conf account sufficient pam_nologin.so account include password-auth account required pam_mysql.so config_file=/etc/pam_mysql.conf password include password-auth # pam_selinux.so close should be the first session rule session required pam_selinux.so close session required pam_loginuid.so # pam_selinux.so open should only be followed by sessions to be executed in the user context session required pam_selinux.so open env_params session optional pam_keyinit.so force revoke session include password-auth And to be complete the contents of some log files.. /var/logs/secure Nov 20 14:52:20 hostname unix_chkpwd[4891]: check pass; user unknown Nov 20 14:52:20 hostname unix_chkpwd[4891]: password check failed for user (testuser) Nov 20 14:52:20 hostname sshd[4880]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=192.168.10.107 user=testuser Nov 20 14:52:22 sftpusers sshd[4880]: Failed password for testuser from 192.168.10.107 port 51849 ssh2 /var/logs/audit/audit.log type=USER_AUTH msg=audit(1353420107.070:812): user pid=5285 uid=0 auid=500 ses=24 subj=unconfined_u:system_r:sshd_t:s0-s0:c0.c1023 msg='op=pubkey acct="testuser" exe="/usr/sbin/sshd" hostname=? addr=192.168.10.107 terminal=ssh res=failed' type=USER_AUTH msg=audit(1353420112.312:813): user pid=5285 uid=0 auid=500 ses=24 subj=unconfined_u:system_r:sshd_t:s0-s0:c0.c1023 msg='op=PAM:authentication acct="testuser" exe="/usr/sbin/sshd" hostname=192.168.10.107 addr=192.168.10.107 terminal=ssh res=failed' type=USER_AUTH msg=audit(1353420112.456:814): user pid=5285 uid=0 auid=500 ses=24 subj=unconfined_u:system_r:sshd_t:s0-s0:c0.c1023 msg='op=password acct="testuser" exe="/usr/sbin/sshd" hostname=? addr=192.168.10.107 terminal=ssh res=failed' I tried to let audit2why explain the problem but it remains silent even though there are some errors. Does anyone see the problem? Thanks! EDIT: Turns out it's almost working with setenforce 0 I can mkdir foobar but if I do a single ls I get an error: Received message too long 16777216

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  • Design by Contract with Microsoft .Net Code Contract

    - by Fredrik N
    I have done some talks on different events and summits about Defensive Programming and Design by Contract, last time was at Cornerstone’s Developer Summit 2010. Next time will be at SweNug (Sweden .Net User Group). I decided to write a blog post about of some stuffs I was talking about. Users are a terrible thing! Protect your self from them ”Human users have a gift for doing the worst possible thing at the worst possible time.” – Michael T. Nygard, Release It! The kind of users Michael T. Nygard are talking about is the users of a system. We also have users that uses our code, the users I’m going to focus on is the users of our code. Me and you and another developers. “Any fool can write code that a computer can understand. Good programmers write code that humans can understand.” – Martin Fowler Good programmers also writes code that humans know how to use, good programmers also make sure software behave in a predictable manner despise inputs or user actions. Design by Contract   Design by Contract (DbC) is a way for us to make a contract between us (the code writer) and the users of our code. It’s about “If you give me this, I promise to give you this”. It’s not about business validations, that is something completely different that should be part of the domain model. DbC is to make sure the users of our code uses it in a correct way, and that we can rely on the contract and write code in a way where we know that the users will follow the contract. It will make it much easier for us to write code with a contract specified. Something like the following code is something we may see often: public void DoSomething(Object value) { value.DoIKnowThatICanDoThis(); } .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; } Where “value” can be uses directly or passed to other methods and later be used. What some of us can easily forget here is that the “value” can be “null”. We will probably not passing a null value, but someone else that uses our code maybe will do it. I think most of you (including me) have passed “null” into a method because you don’t know if the argument need to be specified to a valid value etc. I bet most of you also have got the “Null reference exception”. Sometimes this “Null reference exception” can be hard and take time to fix, because we need to search among our code to see where the “null” value was passed in etc. Wouldn’t it be much better if we can as early as possible specify that the value can’t not be null, so the users of our code also know it when the users starts to use our code, and before run time execution of the code? This is where DbC comes into the picture. We can use DbC to specify what we need, and by doing so we can rely on the contract when we write our code. So the code above can actually use the DoIKnowThatICanDoThis() method on the value object without being worried that the “value” can be null. The contract between the users of the code and us writing the code, says that the “value” can’t be null.   Pre- and Postconditions   When working with DbC we are specifying pre- and postconditions.  Precondition is a condition that should be met before a query or command is executed. An example of a precondition is: “The Value argument of the method can’t be null”, and we make sure the “value” isn’t null before the method is called. Postcondition is a condition that should be met when a command or query is completed, a postcondition will make sure the result is correct. An example of a postconditon is “The method will return a list with at least 1 item”. Commands an Quires When using DbC, we need to know what a Command and a Query is, because some principles that can be good to follow are based on commands and queries. A Command is something that will not return anything, like the SQL’s CREATE, UPDATE and DELETE. There are two kinds of Commands when using DbC, the Creation commands (for example a Constructor), and Others. Others can for example be a Command to add a value to a list, remove or update a value etc. //Creation commands public Stack(int size) //Other commands public void Push(object value); public void Remove(); .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; }   A Query, is something that will return something, for example an Attribute, Property or a Function, like the SQL’s SELECT.   There are two kinds of Queries, the Basic Queries  (Quires that aren’t based on another queries), and the Derived Queries, queries that is based on another queries. Here is an example of queries of a Stack: //Basic Queries public int Count; public object this[int index] { get; } //Derived Queries //Is related to Count Query public bool IsEmpty() { return Count == 0; } .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; } To understand about some principles that are good to follow when using DbC, we need to know about the Commands and different Queries. The 6 Principles When working with DbC, it’s advisable to follow some principles to make it easier to define and use contracts. The following DbC principles are: Separate commands and queries. Separate basic queries from derived queries. For each derived query, write a postcondition that specifies what result will be returned, in terms of one or more basic queries. For each command, write a postcondition that specifies the value of every basic query. For every query and command, decide on a suitable precondition. Write invariants to define unchanging properties of objects. Before I will write about each of them I want you to now that I’m going to use .Net 4.0 Code Contract. I will in the rest of the post uses a simple Stack (Yes I know, .Net already have a Stack class) to give you the basic understanding about using DbC. A Stack is a data structure where the first item in, will be the first item out. Here is a basic implementation of a Stack where not contract is specified yet: public class Stack { private object[] _array; //Basic Queries public uint Count; public object this[uint index] { get { return _array[index]; } set { _array[index] = value; } } //Derived Queries //Is related to Count Query public bool IsEmpty() { return Count == 0; } //Is related to Count and this[] Query public object Top() { return this[Count]; } //Creation commands public Stack(uint size) { Count = 0; _array = new object[size]; } //Other commands public void Push(object value) { this[++Count] = value; } public void Remove() { this[Count] = null; Count--; } } .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; }   Note: The Stack is implemented in a way to demonstrate the use of Code Contract in a simple way, the implementation may not look like how you would implement it, so don’t think this is the perfect Stack implementation, only used for demonstration.   Before I will go deeper into the principles I will simply mention how we can use the .Net Code Contract. I mention before about pre- and postcondition, is about “Require” something and to “Ensure” something. When using Code Contract, we will use a static class called “Contract” and is located in he “System.Diagnostics.Contracts” namespace. The contract must be specified at the top or our member statement block. To specify a precondition with Code Contract we uses the Contract.Requires method, and to specify a postcondition, we uses the Contract.Ensure method. Here is an example where both a pre- and postcondition are used: public object Top() { Contract.Requires(Count > 0, "Stack is empty"); Contract.Ensures(Contract.Result<object>() == this[Count]); return this[Count]; } .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; }   The contract above requires that the Count is greater than 0, if not we can’t get the item at the Top of a Stack. We also Ensures that the results (By using the Contract.Result method, we can specify a postcondition that will check if the value returned from a method is correct) of the Top query is equal to this[Count].   1. Separate Commands and Queries   When working with DbC, it’s important to separate Command and Quires. A method should either be a command that performs an Action, or returning information to the caller, not both. By asking a question the answer shouldn’t be changed. The following is an example of a Command and a Query of a Stack: public void Push(object value) public object Top() .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; }   The Push is a command and will not return anything, just add a value to the Stack, the Top is a query to get the item at the top of the stack.   2. Separate basic queries from derived queries There are two different kinds of queries,  the basic queries that doesn’t rely on another queries, and derived queries that uses a basic query. The “Separate basic queries from derived queries” principle is about about that derived queries can be specified in terms of basic queries. So this principles is more about recognizing that a query is a derived query or a basic query. It will then make is much easier to follow the other principles. The following code shows a basic query and a derived query: //Basic Queries public uint Count; //Derived Queries //Is related to Count Query public bool IsEmpty() { return Count == 0; } .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; }   We can see that IsEmpty will use the Count query, and that makes the IsEmpty a Derived query.   3. For each derived query, write a postcondition that specifies what result will be returned, in terms of one or more basic queries.   When the derived query is recognize we can follow the 3ed principle. For each derived query, we can create a postcondition that specifies what result our derived query will return in terms of one or more basic queries. Remember that DbC is about contracts between the users of the code and us writing the code. So we can’t use demand that the users will pass in a valid value, we must also ensure that we will give the users what the users wants, when the user is following our contract. The IsEmpty query of the Stack will use a Count query and that will make the IsEmpty a Derived query, so we should now write a postcondition that specified what results will be returned, in terms of using a basic query and in this case the Count query, //Basic Queries public uint Count; //Derived Queries public bool IsEmpty() { Contract.Ensures(Contract.Result<bool>() == (Count == 0)); return Count == 0; } The Contract.Ensures is used to create a postcondition. The above code will make sure that the results of the IsEmpty (by using the Contract.Result to get the result of the IsEmpty method) is correct, that will say that the IsEmpty will be either true or false based on Count is equal to 0 or not. The postcondition are using a basic query, so the IsEmpty is now following the 3ed principle. We also have another Derived Query, the Top query, it will also need a postcondition and it uses all basic queries. The Result of the Top method must be the same value as the this[] query returns. //Basic Queries public uint Count; public object this[uint index] { get { return _array[index]; } set { _array[index] = value; } } //Derived Queries //Is related to Count and this[] Query public object Top() { Contract.Ensures(Contract.Result<object>() == this[Count]); return this[Count]; } .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; }   4. For each command, write a postcondition that specifies the value of every basic query.   For each command we will create a postconditon that specifies the value of basic queries. If we look at the Stack implementation we will have three Commands, one Creation command, the Constructor, and two others commands, Push and Remove. Those commands need a postcondition and they should include basic query to follow the 4th principle. //Creation commands public Stack(uint size) { Contract.Ensures(Count == 0); Count = 0; _array = new object[size]; } //Other commands public void Push(object value) { Contract.Ensures(Count == Contract.OldValue<uint>(Count) + 1); Contract.Ensures(this[Count] == value); this[++Count] = value; } public void Remove() { Contract.Ensures(Count == Contract.OldValue<uint>(Count) - 1); this[Count] = null; Count--; } .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; }   As you can see the Create command will Ensures that Count will be 0 when the Stack is created, when a Stack is created there shouldn’t be any items in the stack. The Push command will take a value and put it into the Stack, when an item is pushed into the Stack, the Count need to be increased to know the number of items added to the Stack, and we must also make sure the item is really added to the Stack. The postconditon of the Push method will make sure the that old value of the Count (by using the Contract.OldValue we can get the value a Query has before the method is called)  plus 1 will be equal to the Count query, this is the way we can ensure that the Push will increase the Count with one. We also make sure the this[] query will now contain the item we pushed into the Stack. The Remove method must make sure the Count is decreased by one when the top item is removed from the Stack. The Commands is now following the 4th principle, where each command now have a postcondition that used the value of basic queries. Note: The principle says every basic Query, the Remove only used one Query the Count, it’s because this command can’t use the this[] query because an item is removed, so the only way to make sure an item is removed is to just use the Count query, so the Remove will still follow the principle.   5. For every query and command, decide on a suitable precondition.   We have now focused only on postcondition, now time for some preconditons. The 5th principle is about deciding a suitable preconditon for every query and command. If we starts to look at one of our basic queries (will not go through all Queries and commands here, just some of them) the this[] query, we can’t pass an index that is lower then 1 (.Net arrays and list are zero based, but not the stack in this blog post ;)) and the index can’t be lesser than the number of items in the stack. So here we will need a preconditon. public object this[uint index] { get { Contract.Requires(index >= 1); Contract.Requires(index <= Count); return _array[index]; } } .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; } Think about the Contract as an documentation about how to use the code in a correct way, so if the contract could be specified elsewhere (not part of the method body), we could simply write “return _array[index]” and there is no need to check if index is greater or lesser than Count, because that is specified in a “contract”. The implementation of Code Contract, requires that the contract is specified in the code. As a developer I would rather have this contract elsewhere (Like Spec#) or implemented in a way Eiffel uses it as part of the language. Now when we have looked at one Query, we can also look at one command, the Remove command (You can see the whole implementation of the Stack at the end of this blog post, where precondition is added to more queries and commands then what I’m going to show in this section). We can only Remove an item if the Count is greater than 0. So we can write a precondition that will require that Count must be greater than 0. public void Remove() { Contract.Requires(Count > 0); Contract.Ensures(Count == Contract.OldValue<uint>(Count) - 1); this[Count] = null; Count--; } .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; }   6. Write invariants to define unchanging properties of objects.   The last principle is about making sure the object are feeling great! This is done by using invariants. When using Code Contract we can specify invariants by adding a method with the attribute ContractInvariantMethod, the method must be private or public and can only contains calls to Contract.Invariant. To make sure the Stack feels great, the Stack must have 0 or more items, the Count can’t never be a negative value to make sure each command and queries can be used of the Stack. Here is our invariant for the Stack object: [ContractInvariantMethod] private void ObjectInvariant() { Contract.Invariant(Count >= 0); } .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; }   Note: The ObjectInvariant method will be called every time after a Query or Commands is called. Here is the full example using Code Contract:   public class Stack { private object[] _array; //Basic Queries public uint Count; public object this[uint index] { get { Contract.Requires(index >= 1); Contract.Requires(index <= Count); return _array[index]; } set { Contract.Requires(index >= 1); Contract.Requires(index <= Count); _array[index] = value; } } //Derived Queries //Is related to Count Query public bool IsEmpty() { Contract.Ensures(Contract.Result<bool>() == (Count == 0)); return Count == 0; } //Is related to Count and this[] Query public object Top() { Contract.Requires(Count > 0, "Stack is empty"); Contract.Ensures(Contract.Result<object>() == this[Count]); return this[Count]; } //Creation commands public Stack(uint size) { Contract.Requires(size > 0); Contract.Ensures(Count == 0); Count = 0; _array = new object[size]; } //Other commands public void Push(object value) { Contract.Requires(value != null); Contract.Ensures(Count == Contract.OldValue<uint>(Count) + 1); Contract.Ensures(this[Count] == value); this[++Count] = value; } public void Remove() { Contract.Requires(Count > 0); Contract.Ensures(Count == Contract.OldValue<uint>(Count) - 1); this[Count] = null; Count--; } [ContractInvariantMethod] private void ObjectInvariant() { Contract.Invariant(Count >= 0); } } .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; } Summary By using Design By Contract we can make sure the users are using our code in a correct way, and we must also make sure the users will get the expected results when they uses our code. This can be done by specifying contracts. To make it easy to use Design By Contract, some principles may be good to follow like the separation of commands an queries. With .Net 4.0 we can use the Code Contract feature to specify contracts.

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  • How to deploy asp.net web application multiple times on the same server?

    - by Sergey
    Hello, I have a ASP.NET 3.5 web application and I would like to allow users to install this web application multiple times on the same server. Each web app will work with it's own database: Server1 -------- WebApp1 - database1 WebApp2 - database2 WebApp3 - database3 Firstly I tried to use web-deployment-project, but it allows me to install my web application only once. How I should implement deployment of web app multiple times on the same server? Should I develop my own winforms application? Thanks, Sergey

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