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  • Rails always include (join) on initialize

    - by Seth
    Hello, I have a User model as illustrated below: class User < ActiveRecord belongs_to :college belongs_to :class_level end I want to ALWAYS join with those other two tables returning one simplified User object. How do I accomplish this in my User model. I'm aware that I can do this in another model: class Foo < ActiveRecord has_many :users, :include => [:college, :class_level] end But I want to do this in my User model, so Foo.users will either be eager loaded OR be joined already. Is there a way to create an initialize this in the User model?

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  • DRY vs Security and Maintainability with MVC and View Models

    - by Mystere Man
    I like to strive for DRY, and obviously it's not always possible. However, I have to scratch my head over a concept that seems pretty common in MVC, that of the "View Model". The View Model is designed to only pass the minimum amount of information to the view, for both security, maintainability, and testing concerns. I get that. It makes sense. However, from a DRY perspective, a View Model is simply duplicating data you already have. The View Model may be temporary, and used only as a DTO, but you're basically maintaing two different versions of the same model which seems to violate the DRY principal. Do View Models violate DRY? Are they a necessary evil? Do they do more good than bad?

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  • Want to save data field from form into two columns of two models.

    - by vette982
    I have a Profile model with a hasOne relationship to a Detail model. I have a registration form that saves data into both model's tables, but I want the username field from the profile model to be copied over to the usernamefield in the details model so that each has the same username. function new_account() { if(!empty($this->data)) { $this->Profile->modified = date("Y-m-d H:i:s"); if($this->Profile->save($this->data)) { $this->data['Detail']['profile_id'] = $this->Profile->id; $this->data['Detail']['username'] = $this->Profile->username; $this->Profile->Detail->save($this->data); $this->Session->setFlash('Your registration was successful.'); $this->redirect(array('action'=>'index')); } } } This code in my Profile controller gives me the error: Undefined property: Profile::$username Any ideas?

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  • MVC - thin controller idea - Codeigniter/Zend

    - by user505988
    Hi, Could some one possibly clarify this for me. In the MVC paradigm, the idea is to keep the controller as thin as possible, it is also true that the model is the bit that communicates with data sources such as the database, XML-RPC etc and this is where the business logic should go. Is the POST and GET data a 'data source' and should that kind of data be handled by the model or should it be by the controller. I would normally call a method in the model and pass it the post data, the data would be quality checked by the controller and the model method would simply do the insertion or whatever. Should it be though that controller just calls the model method if a post has occured and it is responsible for sanity check, data checks etc.

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  • Doubt about a particular pattern of Javascript class definition

    - by fenderplayer
    Recently i saw the following code that creates a class in javascript: var Model.Foo = function(){ // private stuff var a, b; // public properties this.attr1 = ''; this.attr2 = ''; if(Model.Foo._init === 'undefined'){ Model.Foo.prototype = { func1 : function(){ //...}, func2 : function(){ //... }, //other prototype functions } } Model.Foo._init = true; } // Instantiate and use the class as follows: var foo = new Model.Foo(); foo.func1(); I guess the _init variable is used to make sure we don't define the prototypes again. Also, i feel the code is more readable since i am placing everything in a function block (so in oop-speak, all attributes and methods are in one place). Do you see any issues with the code above? Any pitfalls of using this pattern if i need to create lots of classes in a big project?

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  • Django forms: prepopulate form with request.user and url parameter

    - by Malyo
    I'm building simple Course Management App. I want Users to sign up for Course. Here's sign up model: class CourseMembers(models.Model): student = models.ForeignKey(Student) course = models.ForeignKey(Course) def __unicode__(self): return unicode(self.student) Student model is extended User model - I'd like to fill the form with request.user. In Course model most important is course_id, which i'm passing into view throught URL parameter (for example http://127.0.0.1:8000/courses/course/1/). What i want to achieve, is to generate 'invisible' (so user can't change the inserted data) form with just input, but containing request.user and course_id parameter.

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  • web service data type (contract)

    - by cyberguest
    hi, i have a general design question. we have a fairly big data model that represents an clinical object, the object itself has 200+ child attributes in the hierarchy. and we have a SetObject operation, and a GetObject operation. my question is, best practice wise, would it make sense to use that single data model in both operations or different data model for each? Because the Get operation will return much more details than what's needed for Set. an example of what i mean: the data model has say ProviderId, and ProviderName attributes, in the Get operation, both the ProviderId, and ProviderName would need to be returned. However, in the Set operation, only the ProviderId is needed, and ProviderName is ignored by the service since system has that information already. In this case, if the Get and Set operations use the same data model, the ProviderName is exposed even for Set operation, does that confuse the consuming developer?

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  • How do I filter values in a Django form using ModelForm?

    - by malandro95
    I am trying to use the ModelForm to add my data. It is working well, except that the ForeignKey dropdown list is showing all values and I only want it to display the values that a pertinent for the logged in user. Here is my model for ExcludedDate, the record I want to add: class ExcludedDate(models.Model): date = models.DateTimeField() reason = models.CharField(max_length=50) user = models.ForeignKey(User) category = models.ForeignKey(Category) recurring = models.ForeignKey(RecurringExclusion) def __unicode__(self): return self.reason Here is the model for the category, which is the table containing the relationship that I'd like to limit by user: class Category(models.Model): name = models.CharField(max_length=50) user = models.ForeignKey(User, unique=False) def __unicode__(self): return self.name And finally, the form code: class ExcludedDateForm(ModelForm): class Meta: model = models.ExcludedDate exclude = ('user', 'recurring',) How do I get the form to display only the subset of categories where category.user equals the logged in user?

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  • How do submit an object to a struts2 action using jQuery?

    - by James Drinkard
    I have an object that I'm populating from a selection off a table row that a user selects. I have a jQuery function that captures the click event and a hidden form field populates an id I need. However, I'm not sure as to the proper way to send off that object to a struts2 action? I tried using this: $(function() { $('#tbl tr').click(function() { var id = $(this).closest('tr').find('input:hidden').val(); var page = "<s:url action='update/deleteInfo.action'/>?model.isDelete=true&model.info.id=id"; console.log(page); window.location.href=(page); }); }); The model object has an isDelete boolean variable and the model has a nested info object that has an id variable with getter/setters. However, when I send this across, the model object isn't populated with these entries. Is there a way to do this or a better way than the url tag?

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  • Windows Explorer is blank

    - by Scott Mitchell
    I am using Windows 7 Utlimate x64. Once a week, or so, when I boot up n the morning and launch Windows Explorer it shows up blank, as the following screen shot show. Clicking on my Computer doesn't load anything. Interestingly, I can go the the Address bar at the top and type in a folder name. This brings up that folder's files and subfolders, but as I drill around the tree of folders on the left only shows the immediate folder and not its siblings. There's no plus icon to expand the folder, etc. My usual "solution" is to reboot, which typically brings everything back to normal, but this is a frustrating remedy. Any idea what's going on and how to fix it? Some Googling turned up this discussion, but the remedy was to uninstall a particular piece of software that I don't have installed (Virtual Clone Drive). Thanks

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  • samba4 dc "network location cannot be reached"

    - by mitchell babies peters
    to clear the air centos 6.4? (maybe 6.3) as the server, running samba 4.0.10, trying to add a windows 7 client that has connectivity to the server. this is what windows shouts as me as it mocks my dependence on network infrastructure. "the network location cannot be reached." i have access to the domain contoller (dc) im using the dc as the domain name server (dns) already, and the name is correctly resolving, and it is correctly forwarding outbound traffic. i have nothing but self taught experience with active directory(ad) so if i am missing something obvious, please shout it out, but keep the verbal abuse to a minimum. i checked samba4DC + my error and found nothing relevant to my issue, if i missed something please point me in that direction. the weekend is just starting as i write this so i probably wont be back on to check this post for a day or three, but i might because this mystery is killing me. i followed the samba4 as a dc guide here and i supplimented gaps with this i have tested kerberos, ntp, and set my DC as the clock to sync to in my windows client and it appears to be a very small fraction of a second off so that shouldn't be it. also, firewall and selinux are both off for testing. i have also tried disabling ipv6, and cleared the registry of ipv6 records (allegedly the default samba4 as a DC runs as windows server 2003 which allegedly does not support or tolerate the existence of ipv6, fair warning, i heard this on the internet so it is probably a lie) i have tried a few other things that i have forgotten because i have been doing this for a day and a half now. ideas welcome. suggestions for alternatives are also welcome, as long as they are free. i was given a budget of $0 dollars and told to implement active directory (no prior knowledge of active directory at that point).

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  • Links won't open in Outlook

    - by Scott Mitchell
    About a week ago Chrome (my default browser) stopped working and I ended up reinstalling. After that, however, links in Outlook 2007, when clicked, no longer open. Instead, I get a warning that reads: General failure. The URL was: URL. Application not found. I presume that there is some MIME or file type association that needs to be configured at the OS level, but I've not had any luck so far. My operating system is Windows 7. Any ideas? EDIT #1 Wayne Johnston suggested I set Chrome as my default browser, but when I go to the Set Default Programs screen in Windows 7 (via Control Panel) I do not see Chrome in the list of programs. How do I get it to show up there?

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  • Diagnosing Microsoft SQL Server error 9001: The log for the database is not available.

    - by Scott Mitchell
    Over the weekend a website I run stopped functioning, recording the following error in the Event Viewer each time a request is made to the website: Event ID: 9001 The log for database 'database name' is not available. Check the event log for related error messages. Resolve any errors and restart the database. The website is hosted on a dedicated server, so I am able to RDP into the server and poke around. The LDF file for the database exists in the C:\Program Files\Microsoft SQL Server\MSSQL10.MSSQLSERVER\MSSQL\DATA folder, but attempting to do any work with the database from Management Studio results in a dialog box reporting the same error - 9001: The log for database is not available... This is the first time I've received this error, and I've been hosting this site (and others) on this dedicated web server for over two years now. It is my understanding that this error indicates a corrupt log file. I was able to get the website back online by Detaching the database and then restoring a backup from a couple days ago, but my concern is that this error is indicative of a more sinister problem, namely a hard drive failure. I emailed support at the web hosting company and this was their reply: There doesn't appear to be any other indications of the cause in the Event Log, so it's possible that the log was corrupted. Currently the memory's resources is at 87%, which also may have an impact but is unlikely. Can the log just "become corrupted?" My question: What are the next steps I should take to diagnose this problem? How can I determine if this is, indeed, a hardware problem? And if it is, are there any options beyond replacing the disk? Thanks

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  • Diagnosing Logon Audit Failure event log entries

    - by Scott Mitchell
    I help a client manage a website that is run on a dedicated web server at a hosting company. Recently, we noticed that over the last two weeks there have been tens of thousands of Audit Failure entries in the Security Event Log with Task Category of Logon - these have been coming in about every two seconds, but interesting stopped altogether as of two days ago. In general, the event description looks like the following: An account failed to log on. Subject: Security ID: SYSTEM Account Name: ...The Hosting Account... Account Domain: ...The Domain... Logon ID: 0x3e7 Logon Type: 10 Account For Which Logon Failed: Security ID: NULL SID Account Name: david Account Domain: ...The Domain... Failure Information: Failure Reason: Unknown user name or bad password. Status: 0xc000006d Sub Status: 0xc0000064 Process Information: Caller Process ID: 0x154c Caller Process Name: C:\Windows\System32\winlogon.exe Network Information: Workstation Name: ...The Domain... Source Network Address: 173.231.24.18 Source Port: 1605 The value in the Account Name field differs. Above you see "david" but there are ones with "john", "console", "sys", and even ones like "support83423" and whatnot. The Logon Type field indicates that the logon attempt was a remote interactive attempt via Terminal Services or Remote Desktop. My presumption is that these are some brute force attacks attempting to guess username/password combinations in order to log into our dedicated server. Are these presumptions correct? Are these types of attacks pretty common? Is there a way to help stop these types of attacks? We need to be able to access the desktop via Remote Desktop so simply turning off that service is not feasible. Thanks

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  • Exchange 2010 Room Mailbox Calendar Permissions

    - by Brian Mitchell
    Exchange 2010 sp2 Outlook 2007/2010 Server 2008 I have managed to set up several room mailboxes in exchange, people are able to book the rooms and they get a response from the exchange server. this is brilliant. however users are unable to view the calendar of the room mailbox to see what times are available, in a ideal world I would like users to only see if the room is free or not. I dont want users to see the details of the meeting (title, description etc) I have been trying to do this using the following command Add-MailboxFolderPermission -Identity meetingroom -User "Usergroup" -AccessRights AvailabilityOnly -DomainController AD-Server This throws the following error Specified argument was out of the range of valid values. Parameter name: memberRights + CategoryInfo : NotSpecified: (meetingroom:MailboxFolderIdParameter) [Add-MailboxFolderPermission], Argum entOutOfRangeException + FullyQualifiedErrorId : CBC6516F,Microsoft.Exchange.Management.StoreTasks.AddMailboxFolderPermission Any help on the situation would be brilliant, i have been trying to get this done for a couple of days and im going around in circles.

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  • sendmail - DSN: Name Server host not found

    - by Daniel Mitchell
    I've recently setup a new backup server and have configured sendmail with a smart_relay_host Except every email from the command line doesn't go anywhere. From mail.log: Oct 3 14:32:52 **back01 sm-mta[16570]: p93DWqtC016568: to=<[email protected], ctladdr= (0/0), delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=120762, relay=10.2.30.60, dsn=5.1.2, stat=Host unknown (Name server: 10.2.30.60: host not found) Oct 3 14:32:52 ***back01 sm-mta[16570]: p93DWqtC016568: p93DWqtC016570: DSN: Host unknown (Name server: 10.2.30.60: host not found) DNS is working correctly on this box. I can do forward and reverse lookups. I can also telnet to the mail relay and send a message that way. I'm stumped, any suggestions?

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  • Server 2008 R2 Datacenter (and all other version) not detecting hardware

    - by Mitchell Skurnik
    I upgraded my ASUS KFN32-D SLI/SAS motherboard to the latest BIOS version and swapped out the 2 dual-core procs with 2 quad core procs. After installing Server 2008 Datacenter onto the system I noticed that it was not connected to the network. I open device manager and see no network adapters. I have to go up to View - Show hidden devices to even see the virtual WAN Miniport adapters. This problem happens in Vista and Windows 7 (all x64). What is even stranger is it all works in x86 mode. What in x64 could be causing windows to not even detect hardware that works in x86? Is the boot manager possibly the culprit?

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  • SVN Checkout error on large repositories

    - by Brian Mitchell
    I wonder if anyone can help me. We have recently migrated our Subversion repository from a VisualSVN Server on Windows to a subversion server on CentOS. The migration was succesfull however we are getting the following error message Error REPORT of svn'/svn/MangoRepository/!svn/vcc/default': Could not read chunk size: Error connection was closed by server (http://servername) Now the workaround for this is simply to perform a update on the repo and it will contine where is left off. Im just wondering if anyone was a permanent fix for this as it can be quite frustrating to repeat my self to 60-70 developers.

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  • Change Data Capture Webinar

    I am going to be doing a webinar with our friends at Attunity on Change Data Capture.  Attunity have a good story around this technology and you can use it in your SSIS loads to great effect. Join Attunity and Konesans/SQLIS for a Webinar on 17 September Space is limited. Reserve your Webinar seat now at: https://www1.gotomeeting.com/register/693735512 Want increased efficiency and real-time speed when conducting ETL loads? Need lower implementation costs while minimizing system impact? Learn how change data capture (CDC) technologies can reduce ETL load times. Allan Mitchell, Principal Consultant at Konesans and SQLServer MVP specialising in ETL, will explain CDC concepts and benefits and how CDC can dramatically reduce ETL load times. Ian Archibald, Pre-Sales Director EMEA for Attunity, will present and demonstrate Attunity's award-winning Oracle-CDC for SSIS, a fully-integrated SSIS solution for designing, deploying and managing Oracle CDC processes. Title: Change Data Capture - Reducing ETL Load Times Date: Thursday, September 17, 2009 Time: 10:00 AM - 11:00 AM BST ABOUT THE SPEAKERS: Allan Mitchell is the joint owner of Konesans Ltd, a UK based consultancy specializing in SQL Server, and most importantly SQL Server Integration Services. Having been working with SQL Server from 6.5 onwards, he has extensive experience in many aspects of SQL Server, but now focuses on the BI suite of tools. He is a SQL Server MVP, a frequent poster on the MS SSIS/DTS newsgroups, and runs the sqldts.com and sqlis.com resource sites. Ian Archibald, Attunity Pre-Sales Director EMEA, has worked in Attunity’s UK Office for 17 years. An expert in Attunity solutions, Ian has extensive knowledge of Attunity’s products and data integration & CDC technologies. After registering you will receive a confirmation email containing information about joining the Webinar. System Requirements PC-based attendees Required: Windows® 2000, XP Home, XP Pro, 2003 Server, Vista Macintosh®-based attendees Required: Mac OS® X 10.4 (Tiger®) or newer

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  • Change Data Capture Webinar

    I am going to be doing a webinar with our friends at Attunity on Change Data Capture.  Attunity have a good story around this technology and you can use it in your SSIS loads to great effect. Join Attunity and Konesans/SQLIS for a Webinar on 17 September Space is limited. Reserve your Webinar seat now at: https://www1.gotomeeting.com/register/693735512 Want increased efficiency and real-time speed when conducting ETL loads? Need lower implementation costs while minimizing system impact? Learn how change data capture (CDC) technologies can reduce ETL load times. Allan Mitchell, Principal Consultant at Konesans and SQLServer MVP specialising in ETL, will explain CDC concepts and benefits and how CDC can dramatically reduce ETL load times. Ian Archibald, Pre-Sales Director EMEA for Attunity, will present and demonstrate Attunity's award-winning Oracle-CDC for SSIS, a fully-integrated SSIS solution for designing, deploying and managing Oracle CDC processes. Title: Change Data Capture - Reducing ETL Load Times Date: Thursday, September 17, 2009 Time: 10:00 AM - 11:00 AM BST ABOUT THE SPEAKERS: Allan Mitchell is the joint owner of Konesans Ltd, a UK based consultancy specializing in SQL Server, and most importantly SQL Server Integration Services. Having been working with SQL Server from 6.5 onwards, he has extensive experience in many aspects of SQL Server, but now focuses on the BI suite of tools. He is a SQL Server MVP, a frequent poster on the MS SSIS/DTS newsgroups, and runs the sqldts.com and sqlis.com resource sites. Ian Archibald, Attunity Pre-Sales Director EMEA, has worked in Attunity’s UK Office for 17 years. An expert in Attunity solutions, Ian has extensive knowledge of Attunity’s products and data integration & CDC technologies. After registering you will receive a confirmation email containing information about joining the Webinar. System Requirements PC-based attendees Required: Windows® 2000, XP Home, XP Pro, 2003 Server, Vista Macintosh®-based attendees Required: Mac OS® X 10.4 (Tiger®) or newer

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  • Does my use of the strategy pattern violate the fundamental MVC pattern in iOS?

    - by Goodsquirrel
    I'm about to use the 'strategy' pattern in my iOS app, but feel like my approach violates the somehow fundamental MVC pattern. My app is displaying visual "stories", and a Story consists (i.e. has @properties) of one Photo and one or more VisualEvent objects to represent e.g. animated circles or moving arrows on the photo. Each VisualEvent object therefore has a eventType @property, that might be e.g. kEventTypeCircle or kEventTypeArrow. All events have things in common, like a startTime @property, but differ in the way they are being drawn on the StoryPlayerView. Currently I'm trying to follow the MVC pattern and have a StoryPlayer object (my controller) that knows about both the model objects (like Story and all kinds of visual events) and the view object StoryPlayerView. To chose the right drawing code for each of the different visual event types, my StoryPlayer is using a switch statement. @implementation StoryPlayer // (...) - (void)showVisualEvent:(VisualEvent *)event onStoryPlayerView:storyPlayerView { switch (event.eventType) { case kEventTypeCircle: [self showCircleEvent:event onStoryPlayerView:storyPlayerView]; break; case kEventTypeArrow: [self showArrowDrawingEvent:event onStoryPlayerView:storyPlayerView]; break; // (...) } But switch statements for type checking are bad design, aren't they? According to Uncle Bob they lead to tight coupling and can and should almost always be replaced by polymorphism. Having read about the "Strategy"-Pattern in Head First Design Patterns, I felt this was a great way to get rid of my switch statement. So I changed the design like this: All specialized visual event types are now subclasses of an abstract VisualEvent class that has a showOnStoryPlayerView: method. @interface VisualEvent : NSObject - (void)showOnStoryPlayerView:(StoryPlayerView *)storyPlayerView; // abstract Each and every concrete subclass implements a concrete specialized version of this drawing behavior method. @implementation CircleVisualEvent - (void)showOnStoryPlayerView:(StoryPlayerView *)storyPlayerView { [storyPlayerView drawCircleAtPoint:self.position color:self.color lineWidth:self.lineWidth radius:self.radius]; } The StoryPlayer now simply calls the same method on all types of events. @implementation StoryPlayer - (void)showVisualEvent:(VisualEvent *)event onStoryPlayerView:storyPlayerView { [event showOnStoryPlayerView:storyPlayerView]; } The result seems to be great: I got rid of the switch statement, and if I ever have to add new types of VisualEvents in the future, I simply create new subclasses of VisualEvent. And I won't have to change anything in StoryPlayer. But of cause this approach violates the MVC pattern since now my model has to know about and depend on my view! Now my controller talks to my model and my model talks to the view calling methods on StoryPlayerView like drawCircleAtPoint:color:lineWidth:radius:. But this kind of calls should be controller code not model code, right?? Seems to me like I made things worse. I'm confused! Am I completely missing the point of the strategy pattern? Is there a better way to get rid of the switch statement without breaking model-view separation?

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  • 30 Steps to Master ASP.NET MVC Application development

    - by Rajesh Pillai
    Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 st1\:*{behavior:url(#ieooui) } /* 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:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman","serif";} Welcome Readers!,   I am starting out a new series on ASP.NET  MVC skill building which will be posted over the next couple of weeks.  Let me know your thoughts on the content, which I have planned and a couple of them has been taken from ASP.NET MVC2 Cookbook. (NOTE: Only the heading has been taken, the content will be not :)).   Do let me know what you would like to see, or any additional inputs or ideas to cover in this topics.  The 30 steps are oultined below for quick reference.  Will start filling this out quickly.   Outlined is the ‘30’ step to master ASP.NET MVC.   A Peek Into Model What is a model? Different types of model Presentation/ViewModel Model Mapping (AutoMapper)   A Peak into View How view works in ASP.NET MVC? View Engine Design Custom View Engine View Best Practices Templated Helpers Partial Views   A Peak into Controller Introduction Controller Design Controller Best Practices Asynchronous Controller Custom Action Result Action Filters Controller Factory to use with IOC   Routes Explanation Routes from the database Routes from XML More complex routing   Master Pages Basics Setting Master Page Dynamically   Working with data in the view Repeating Views Array of check boxes Array of radio buttons Paged data CRUD Client side action Confirmation Dialog (modal window) jqGrid   Working with Forms   Validation Model Validation with DataAnnotations Using the xVal validation framework Client side validation with jQuery Validation Fluent Validation Model Binders   Templating Create strongly typed helper using T4 Custom View Templates with T4 Create custom MVC project template using T4   IOC AutoFac Ninject Unity Application   Areas   jQuery, Ajax and jQuery Plugins   State Maintenance Application State User state Cookies Webfarm   Error Handling View error handling Controller error handling ELMAH (Error Logging Modules and Handlers)   Authentication and Authorization User Registration form SignOn Process Password Reminder Membership and Roles Windows authentication Restricting access to all pages Restricting access to selected pages Restricting access to pages by role Restricting access to a controller Restricting access to selected area   Profiles and Themes Using Profiles Inheriting a Profile Migrating an anonymous profile Creating custom themes Using themes User personalized themes   Configuration Adding custom application settings in web.config Displaying custom error messages Accessing other web.config configuration elements Adding custom configuration elements to web.config Encrypting web.config sections   Tracing, Debugging and Logging   Caching Caching a whole page Caching pages based on route details Caching pages based on browser type and version Caching pages based custom strings Caching partial pages Caching application data Object Caching Using Microsoft Velocity Using MemCache Using AppFabric cache   Localization   HTTP Handlers and Modules   Security XSS/CSRF AnitForgery Encoding   HtmlHelpers Strongly typed helpers Writing custom helpers   Repository Pattern (Data access)   WF/WCF   Unit Testing   Mocking Framework   Integration Testing   Load / Performance Testing   Deployment    Once again let me know your thoughts on this.   Till then, Enjoy MVC'ing!!!

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  • C# 5 Async, Part 2: Asynchrony Today

    - by Reed
    The .NET Framework has always supported asynchronous operations.  However, different mechanisms for supporting exist throughout the framework.  While there are at least three separate asynchronous patterns used through the framework, only the latest is directly usable with the new Visual Studio Async CTP.  Before delving into details on the new features, I will talk about existing asynchronous code, and demonstrate how to adapt it for use with the new pattern. The first asynchronous pattern used in the .NET framework was the Asynchronous Programming Model (APM).  This pattern was based around callbacks.  A method is used to start the operation.  It typically is named as BeginSomeOperation.  This method is passed a callback defined as an AsyncCallback, and returns an object that implements IAsyncResult.  Later, the IAsyncResult is used in a call to a method named EndSomeOperation, which blocks until completion and returns the value normally directly returned from the synchronous version of the operation.  Often, the EndSomeOperation call would be called from the callback function passed, which allows you to write code that never blocks. While this pattern works perfectly to prevent blocking, it can make quite confusing code, and be difficult to implement.  For example, the sample code provided for FileStream’s BeginRead/EndRead methods is not simple to understand.  In addition, implementing your own asynchronous methods requires creating an entire class just to implement the IAsyncResult. Given the complexity of the APM, other options have been introduced in later versions of the framework.  The next major pattern introduced was the Event-based Asynchronous Pattern (EAP).  This provides a simpler pattern for asynchronous operations.  It works by providing a method typically named SomeOperationAsync, which signals its completion via an event typically named SomeOperationCompleted. The EAP provides a simpler model for asynchronous programming.  It is much easier to understand and use, and far simpler to implement.  Instead of requiring a custom class and callbacks, the standard event mechanism in C# is used directly.  For example, the WebClient class uses this extensively.  A method is used, such as DownloadDataAsync, and the results are returned via the DownloadDataCompleted event. While the EAP is far simpler to understand and use than the APM, it is still not ideal.  By separating your code into method calls and event handlers, the logic of your program gets more complex.  It also typically loses the ability to block until the result is received, which is often useful.  Blocking often requires writing the code to block by hand, which is error prone and adds complexity. As a result, .NET 4 introduced a third major pattern for asynchronous programming.  The Task<T> class introduced a new, simpler concept for asynchrony.  Task and Task<T> effectively represent an operation that will complete at some point in the future.  This is a perfect model for thinking about asynchronous code, and is the preferred model for all new code going forward.  Task and Task<T> provide all of the advantages of both the APM and the EAP models – you have the ability to block on results (via Task.Wait() or Task<T>.Result), and you can stay completely asynchronous via the use of Task Continuations.  In addition, the Task class provides a new model for task composition and error and cancelation handling.  This is a far superior option to the previous asynchronous patterns. The Visual Studio Async CTP extends the Task based asynchronous model, allowing it to be used in a much simpler manner.  However, it requires the use of Task and Task<T> for all operations.

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  • Removing Barriers to Create Effective Data Models

    After years of creating and maintaining data models, I have started to notice common barriers that decrease the accuracy and usefulness of models. In my opinion, the main causes of these barriers are the lack of knowledge and communication from within a company. The lack of knowledge in regards to data models or data modeling can take many forms. Company Culture Knowledge Whether documented or undocumented, existing business rules of a company can affect how data is modeled. For example, if a company only allows 1 assigned person per customer to be able to manipulate a customer’s record then then a data model that includes an associated table that joins customers and employee’s would be unneeded because that would allow for the possibility of multiple employees to handle a customer because of the potential for a many to many relationship between Customers and Employees. Technical Knowledge Depending on the data modeler’s proficiency in modeling data they can inadvertently cause issues and/or complications with a design without even noticing. It is important that companies share data modeling responsibilities so that the models are developed from multiple perspectives of a system, company and the original problem.  In addition, the tools that a company selects to create data models can also affect the accuracy of the model if designer are not familiar with the tools or the tools are too complex to use for the designer. Existing System Knowledge In order for a data modeler to model data for an existing system so that new changes can be applied to a system then they need to at least know the basic concepts of a system so that they can work within it. This will promote reusability of data and prevent the chance of duplicating data. Project Knowledge This should be pretty obvious, but it is very hard to create an accurate data model without knowing what data needs to be modeled. I have always found it strange that I have been asked to start modeling data prior to a client formalizing any requirements. Usually when this happens I have to make several iterations to a model, and the client still does not know exactly what they want.  In addition additional issues can arise when certain stakeholders of a project are not consulted prior to the design or after the project is over because it can cause miss understandings and confusion by the end user as well as possibly not solving the original problem for which a project is intended to solve. One common thread between each type of knowledge is that they can all be avoided through the use of good communication. For example, if a modeler is new to a company then they should ask older employees about any business specific rules that may be documented or undocumented that must be applied to projects in general. Furthermore, if a modeler is not really familiar with a specific data modeling software then they need to speak up and ask for help form other employees or their manager. This will not only help the modeler in the project, but also help them in future projects that they do for the company. Additionally, if a project is not clearly defined prior to a data modeler being assigned the modeling project then it is their responsibility to communicate with the other stakeholders to clarify any part of a project that is unclear so that the data model that is created is accurately aligned with a project.

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  • Come up with a real-world problem in which only the best solution will do (a problem from Introduction to algorithms) [closed]

    - by Mike
    EDITED (I realized that the question certainly needs a context) The problem 1.1-5 in the book of Thomas Cormen et al Introduction to algorithms is: "Come up with a real-world problem in which only the best solution will do. Then come up with one in which a solution that is “approximately” the best is good enough." I'm interested in its first statement. And (from my understanding) it is asked to name a real-world problem where only the exact solution will work as opposed to a real-world problem where good-enough solution will be ok. So what is the difference between the exact and good enough solution. Consider some physics problem for example the simulation of the fulid flow in the permeable medium. To make this simulation happen some simplyfing assumptions have to be made when deriving a mathematical model. Otherwise the model becomes at least complex and unsolvable. Virtually any particle in the universe has its influence on the fluid flow. But not all particles are equal. Those that form the permeable medium are much more influental than the ones located light years away. Then when the mathematical model needs to be solved an exact solution can rarely be found unless the mathematical model is simple enough (wich probably means the model isn't close to reality). We take an approximate numerical method and after hours of coding and days of verification come up with the program or algorithm which is a solution. And if the model and an algorithm give results close to a real problem by some degree that is good enough soultion. Its worth noting the difference between exact solution algorithm and exact computation result. When considering real-world problems and real-world computation machines I believe all physical problems solutions where any calculations are taken can not be exact because universal physical constants are represented approximately in the computer. Any numbers are represented with the limited precision, at least limited by amount of memory available to computing machine. I can imagine plenty of problems where good-enough, good to some degree solution will work, like train scheduling, automated trading, satellite orbit calculation, health care expert systems. In that cases exact solutions can't be derived due to constraints on computation time, limitations in computer memory or due to the nature of problems. I googled this question and like what this guy suggests: there're kinds of mathematical problems that need exact solutions (little note here: because the question is taken from the book "Introduction to algorithms" the term "solution" means an algorithm or a program, which in this case gives exact answer on each input). But that's probably more of theoretical interest. So I would like to narrow down the question to: What are the real-world practical problems where only the best (exact) solution algorithm or program will do (but not the good-enough solution)? There are problems like breaking of cryptographic ciphers where only exact solution matters in practice and again in practice the process of deciphering without knowing a secret should take reasonable amount of time. Returning to the original question this is the problem where good-enough (fast-enough) solution will do there's no practical need in instant crack though it's desired. So the quality of "best" can be understood in any sense: exact, fastest, requiring least memory, having minimal possible network traffic etc. And still I want this question to be theoretical if possible. In a sense that there may be example of computer X that has limited resource R of amount Y where the best solution to problem P is the one that takes not more than available Y for inputs of size N*Y. But that's the problem of finding solution for P on computer X which is... well, good enough. My final thought that we live in a world where it is required from programming solutions to practical purposes to be good enough. In rare cases really very very good but still not the best ones. Isn't it? :) If it's not can you provide an example? Or can you name any such unsolved problem of practical interest?

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