Fortunately, Entity Framework does support this technique:

Timestamp column with code-first approach

For the code-first approach, you need to declare a column of type Byte[], and then decorate it with the Timestamp attribute. This way, Entity Framework will know this column must be included in the Where clause of SQL sentences for Updates and Deletes actions.

using System;
using System.ComponentModel.DataAnnotations;

namespace MyProject.Entities
{
   public class Person
   {
      public Int64 Id { get; set; }
      public string Name { get; set; }
      public DateTime BirthDate { get; set; }
      public string EMail { get; set; } 

      [Timestamp]
      public Byte[] Timestamp { get; set; }
   }
}

Now you need to update your EF model and re-create the database structure, so the new column will be created in the table.

And voila! Now you have automatic concurrency checking every time you try to update/delete a row in this table. You can check this column is being included in all row-modifying SQL sentences EF generates. You could use SQL server profiler, for example, to inspect these sentences.

Timestamp column with model-first approach

Now, setting this column with the model-first approach is a little bit trickier. There’s no built-in support for this in EF’s model itself (yet), so we’ll have to hack the code generation template to fulfill our needs.

What we need to do to set up a  timestamp column using model first approach is the following:

1. Add a property named “Timestamp” to the entity in EF’s model
2. Set the type to binary
3. Set nullable to false
4. Set StoreGeneratedPattern to Computed
5. Set ConcurrencyMode to Fixed
6. Create a copy of SSDLToSQL10.tt (typically found in C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\Extensions\Microsoft\Entity Framework Tools\DBGen)
7. Edit the line that says:
   [<#=Id(prop.Name)#>] <#=prop.ToStoreType()#> <#=WriteIdentity(prop, targetVersion)#> <#=WriteNullable(prop.Nullable)#><#=(p < entitySet.ElementType.Properties.Count - 1) ? "," : ""#>
8. Change it to:
   [<#=Id(prop.Name)#>] <#if (string.Compare(prop.Name,"TimeStamp",true) == 0) { #>TIMESTAMP<# } else { #><#=prop.ToStoreType()#><# } #> <#=WriteIdentity(prop, targetVersion)#> <#=WriteNullable(prop.Nullable)#><#=(p < entitySet.ElementType.Properties.Count - 1) ? "," : ""#>
   This will change any column that is called “Timestamp” (case insensitive) to be a Timestamp column.
9. Click on the entity canvas and set the DDL Generation Template to this new copy of the file
10. Click on Generate Database From Model
11. Enjoy your new concurrency-aware data access!

Related posts:

1. Entity Framework
2. Things to consider when using Entity Framework
3. Persistance layer: object-relational mapping tools
4. Sluggish database view? Materialize it!
5. Which database to use for a personal project?

Entity Framework has been designed following the Unit of Work pattern

The Unit of Work pattern is a very well thought data-access pattern. When using this pattern, there’s an object that keeps track of changes made to data, and that coordinates the writing out of changes to the database.

When you use EF, you’ll realize that it creates a context class that inherits from System.Data.Entity.DbContext. This DbContext class is the UnitOfWork object. It keeps track of the changes made to objects, and is responsible for persisting data to the database.

This means that this context keeps a local copy of the data stored in the database along with the changes made. This brings us to the next point:

Entity Framework’s context must be short-lived

The Unit of Work pattern recommends having a UnitOfWork object per transaction. As this object keeps a local copy of the data and the changes made to it, it must be quickly stored to the database in case there’s another request for this data.

You can never totally rule out concurrency problems. But, by keeping EF’s context as short-lived as possible, you’ll be minimizing these problems.

There seems to be a recommendation about EF’s context life to be that of a web request in a web application. I agree, as long as that web request is a regular one, just taking a very small amount of database requests to build the page. But, if you’re doing something heavier, like batch-processing some files or calculating some statistics, then you should discard the context as quickly as possible. In these situations I wouldn’t recommend using a web-request-lived context, but one you create and dispose per each database transaction you need.

What about the costs of context instantiation? Wouldn’t that make the application much slower? Well, instantiating an object always consumes resources, but creating a new context instance is not as expensive as you may think. There’s a local cache kept by Entity Framework that makes this process much faster. Besides, disposing of objects that you’re done with as quickly as possible is one of the best practices you could follow as a programmer. That’s something you should be always doing, not only with EF.

By default Entity Framework does not handle concurrency issues

Or put it in some other way: Entity Framework’s default concurrency policy is “Last-Write-Wins”. This policy isn’t the best one available, and if we’re doing something serious we must not use this policy. Entity Framework does support an optimistic concurrency model. When using this policy, an exception will be thrown when trying to save an entity which has been modified since it was retrieved by that instance of the context. We can then capture this exception and handle the error.

An example and explanation of this will not be very short, so I’ll be posting an article explaining how to do this.

Entity Framework might give you some headaches if you’re not aware of these issues. Make sure that you understand them and that you have taken steps to minimize possible problems.

Related posts:

1. Creating a Timestamp column with Entity Framework
2. Entity Framework
3. Persistance layer: object-relational mapping tools
4. Unit testing

Here’s what Entity Framework (EF) has to offer:

• Using EF with the Model First approach, you design a schema of the model you want to implement, and EF generates a database and the code to implement it. Now, that’s what I call saving time! Using this approach, you can get going really really quick.
• If you already have the code for your model, then EF can generate the database to store this model as well as the rest of the code handling persistance to this database, using the Code First approach.
• In case you already have the database, EF can generate the code using the Database First approach.
• EF uses Plain .Net objects (POCOs) with navigational properties to implement your model. Very easy stuff. The way EF lets you interact with the data once it’s retrieved from the DB is piece of cake (not the fact of data retrieval itself, that can get tricky).
• Automatic code generation with T4 templates. Once you have EF set up in your project, there’s a bunch of templates to generate a lot of code for you. That doesn’t mean you must use it, but it’s there for your convenience, in case you think some templates can help you. Me myself I use some of the T4 templates, but not all of them. There’s some things I actually prefer doing manually.
• Self-tracking entities will greatly simplify the process of implementing an over-the-wire scenario, in which you have different layers spanning across different systems and you have to serialize and de-serialize your entities. EF makes this really easy.
• Local caching, to speed up your data access.
• Lazy loading, which can improve overall application performance.
• Support for LINQ (both coming from Microsoft, you would expect this, right?).
• Convention over configuration. The hottest trend in software development. You wouldn’t think EF would miss it, would you? When starting up a new project with EF, the only thing you need to configure are the database server and its name. Nothing else. All other things are taken care of for you. Of course, if you want more control over what EF is doing, you can tweak it to meet your criteria. But that isn’t something you have do right at the beginning. This way, you can be productive much faster.
• Support for the major databases: MS SQL Server (of course), Oracle, MySQL, PostgreSQL, etc…

And last but not least:

• Coming from a big player in the industry like Microsoft, Entity Framework has great resources and a great community behind it. If you ever have a problem with EF, or want to tweak its behavior, chances are you’ll be finding what you need really fast. If you’re a seasoned developer, you’ll find this is one of the most important features of EF.

If you haven’t tried it out yet, don’t wait any longer and see for yourself what I’m talking about!

Related posts:

1. Creating a Timestamp column with Entity Framework
2. Things to consider when using Entity Framework
3. Persistance layer: object-relational mapping tools
4. Which database to use for a personal project?
5. Sluggish database view? Materialize it!

• ASP.NET Core Runtime and Framework
  • Asynchronously Reading and Writing HTTP Requests and Responses.
  • Improvements to HttpRequest handling
  • Asynchronously flushing a response
  • Support for await and Task-Based Asynchronous Modules and Handlers
  • Asynchronous HTTP modules
  • Asynchronous HTTP handlers
  • New ASP.NET Request Validation Features
  • Deferred (”lazy”) request validation
  • Support for unvalidated requests
  • Anti-XSS Library
  • Support for WebSockets Protocol
  • Bundling and Minification
  • Performance Improvements for Web Hosting
    • Key Performance Factors
    • Requirements for New Performance Features
    • Sharing Common Assemblies
    • Using multi-Core JIT compilation for faster startup
    • Tuning garbage collection to optimize for memory
    • Prefetching for web applications
• ASP.NET Web Forms
  • Strongly Typed Data Controls
  • Model Binding
    • Selecting data
    • Value providers
    • Filtering by values from a control
  • HTML Encoded Data-Binding Expressions
  • Unobtrusive Validation
  • HTML5 Updates
• ASP.NET MVC 4
• ASP.NET Web Pages 2
  • New and Updated Site Templates
  • Improved Input Validation
  • Resource Management
  • Enhanced Membership and Authentication
  • Side-by-side Execution
  • Mobile Device Rendering
  • The Maps Helper
• Visual Web Developer 11 Developer Preview.
  • HTML Editor
    • Smart Tasks
    • WAI-ARIA support
    • New HTML5 snippets
    • Extract to user control
    • IntelliSense for code nuggets in attributes
    • Automatic renaming of matching tag when you rename an opening or closing tag
    • Event handler generation
    • Smart indent
    • Auto-reduce statement completion
  • JavaScript Editor
    • Code outlining
    • Brace matching
    • Go to Definition
    • ECMAScript5 support
    • DOM IntelliSense
    • VSDOC signature overloads
    • Implicit references
  • CSS Editor
    • Auto-reduce statement completion
    • Hierarchical indentation
    • CSS hacks support
    • Vendor specific schemas (-moz-, -webkit)
    • Commenting and uncommenting support
    • Color picker
    • Snippets
    • Custom regions
  • Page Inspector
  • Publishing
    • Publish profiles
    • ASP.NET precompilation and merge
  • IIS Express

These are developer previews, which mean that they should be used for testing purposes only, and never in production environments – not yet, at least.

In case you’re interested, Microsoft’s central hub for ASP.NET’s next version articles is ASP.NET vNext section.

Via Microsoft’s ASP.NET web site.

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If we’re using objects in our application and we want to save them, we’ll probably use some data base system. We’ll most likely establish a connection to the data base, create a SQL sentence with the values of the object (or call some kind of stored procedure), and save them to some table. Easy enough, right? Well, this may seem trivial for a small object with 4 or 5 properties. Just consider an object not so small, with 40 or 50 properties. But… what happens with associations? And… what if the object itself contains some other objects? We’ll store them in the data base as well? All of them or just some? What will we do with foreign keys? We can see that, as the application gets more complex, this translation is not so trivial anymore… As a matter of fact, storing objects in the database can become a very usual source of headaches. There are some studies which state that up to 35% of code is dedicated to the role of translating data between the application and the data warehouse.

And this is where Object-Relational Mapping tools come into play. ORM tools applied to databases transform a DB register to a code object and vice-versa, allowing us to abstract away from writing code to directly access the database. This will speed up development and will allow us to follow the mantra of focusing on business functionalities, not on application plumbing.

But, what exactly can an ORM tool helps us with? Well, they usually do some things like:

• Handle object persistance (to a database, for example). You won’t have to write code for this. And remember, less code means less bugs and less headaches.
• Access different databases. Most of these tools support communicating with different database providers (Oracle, MS SQL Server, MySql, Postgre, etc.).
• Cache. Many of these tools offer some way of caching objects in memory, resulting in much faster data access.
• Help with design. Some of these tools also provide some kind of wizard or graphical interface to aid in the design of the schema and/or database, which leads us to the following point:
• Create your database for you. If you have your data schema already modeled, some of these tools will not only handle how to get the data or how to write it. They can also create the database.

You’re already convinced to use an ORM for your project, right? Good. Now take a look at the most popular ORM tools available for .NET:

• Linq to SQL: not really a full-blown ORM, but it does help with data access.
• NHibernate: I would say NHibernate is one of the most mature ORM projects in .NET, and one of the most used as well.
• Entity Framework: Microsoft’s new kid on the block. Its first version didn’t receive very positive comments, but its latest release looks very good indeed.
• LLBLGen Pro: very mature project, although it’s not the simplest of all.
• DataObjects.Net: quite new, but very promising. It already has a lot of interesting features. Definetely worth taking a look at.

In the next post I’ll be covering Entity Framework a bit. Stay tuned!

Related posts:

1. Things to consider when using Entity Framework
2. Entity Framework
3. Creating a Timestamp column with Entity Framework
4. Some open source projects for .NET you should take a look at
5. Which database to use for a personal project?

• Task Parallel Library: this new library, included in the namespace System.Threading.Tasks.Parallel, has new elements to execute tasks in parallel automatically. It’s got, for example, a parallel For loop, and a parallel ForEach loop.
• Parallel LINQ Execution Engine: as you can guess, it’s a parallelized version of Linq to Objects. It’s the same thing, except that it will run in parallel whenever possible.
• Coordination Data Structures: it’s a set of primitives for sincronization and thread-safe collections. For example, we have thread-safe dictionaries, stacks and buffers, and special objects for thread sincronization, such as SpinWait or SpinLock.

Now, the good part about these parallel extensions is that it gets extremely easy to do parallel programming. Just by using these new features, your code will escalate to use as many parallel threads as possible. For example, in a machine with just one processor all your code will execute sequentially, just as always. But, in an 8-core-processor computer, your code will be broken down into 8 different threads, and they all will execute your code in parallel –assuming all 8 cores are available, of course. You can learn more this article from MSDN.

Related posts:

1. Persistance layer: object-relational mapping tools
2. ASP.NET 4.5 and Visual Studio 11
3. Entity Framework
4. Things to consider when using Entity Framework

TDD is a programming methodology that involves two other practices: test first development, and refactoring. First a set of unit tests is written and verified to fail. Then, code to make them pass must be written, and lastly this code is refactored. The aim of TDD is to achieve clean code that works. The main idea around this methodology is that requirements must be translated into automated tests: thus, when these tests pass, all requirements are guaranteed to have been accomplished. The application to be developed must be flexible enough to allow automated tests to be run. Each test should be small enough to exactly determine which piece of code is failing.

Test-driven development cycle

Once a set of requirements has been defined, a new cycle starts:

1. Choose a requirement: select a requirement you understand and about which you can write code both to test it and to implement it.
2. Write a test: the first code you must write is a test to determine whether the requirement is met, accessing the code through its interfaces. This step makes the programmer consider the problem from the client perspective.
3. Verify the test fails: if the test doesn’t fail it’s because this requirement is already implemented, or because the test is incorrect.
4. Write the implementation: Write the simplest code that will make the test pass. Follow the KISS philosophy (Keep It Simple, Stupid!).
5. Run the automated test: Verify whether the whole set of tests are passed.
6. Refactor: usually used to take out duplicate code. Each change should be made in small increments, and with each increment the tests should be re-run.
7. Update the requirements list: once the requirement is met mark it as done. Besides, add more requirements that may have been detected in this cycle or design requirements, like, for example, some functionality that has been decoupled from another one.

Having a repository of tests makes another good practice easier: frequent integration. Integrating our work frequently with the rest of the team allows us to check whether our code is compatible with the rest of the application, and makes it easier to detect bugs in an early phase. It is much easier and cheaper to fix bugs every few hours than facing enormous problems close to a release date.

Generation of tests for each functionality means that programmers can trust the code. This means that we can make big modifications deep in the core of the system that we would otherwise avoid, since we can be certain that, as long as all the tests pass, the code works as intended and the requirements are still met.

Another thing to keep in mind is that programmers must make the unit tests fail. Unit tests must be tested. The idea is to be sure that unit tests really work, and that they’re able to pick up an error whenever it happens.

Advantages

Programmers that use test-driven development from the beginning of a project find that they seldom have the necessity to use a debugger. In the few occasions that a bug is discovered, it is very easy to fix.

Despite of the high initial requirements of this methodology, TDD may provide a great added value to the software development process, producing higher-quality applications in less time. TDD not only offers a simple requirements validation: it can also lead the design of a program. By writing unit tests, a programmer must imagine how customers will be using the functionality, which may avoid some misinterpretations or bad implementations of a functionality.

Limitations

In order to follow the test-driven development methodology, tests must be automated. This may turn out to be rather complex in the following situations:

• Graphical User Interfaces, although there are some partial solutions proposed.
• Distributed Objects, even though Mock Objects may help.
• Data bases: writing tests that work with data bases is quite complex, since you need to put some known data before, and you have to verify that the contents of the database is the expected once the test is done. This makes these kinds of tests costly to develop.

Test-driven development is a programming methodology that should be in place in all organizations that develop software and consider themselves serious. Unfortunately, this is not the case. I hope things start to change in the near future!

Related posts:

1. Improving software quality: automatic testing
2. GUI Testing
3. Unit testing

• NHibernate: NHibernate is a mature, open source object-relational mapper for the .NET framework. It’s actively developed, fully featured and used in thousands of successful projects.
• NUnit: NUnit is a unit-testing framework for all .Net languages, initially ported from  JUnit. It is written entirely in C# and has been completely redesigned to take advantage of many .NET language features, for example custom attributes and other reflection related capabilities. NUnit brings xUnit to all .NET languages
• jQuery: jQuery is a fast and concise JavaScript Library that simplifies HTML document traversing, event handling, animating, and Ajax interactions for rapid web development. jQuery is designed to change the way that you write JavaScript.
• Rhino.Mocks: A dynamic mock object framework for the .Net platform. It’s purpose is to ease testing by allowing the developer to create mock implementations of custom objects and verify the interactions using unit testing.
• MVC Contrib: This is the contrib project for the ASP.NET MVC framework. This project adds additional functionality on top of the MVC Framework. These enhancements can increase your productivity using the MVC Framework. It is written in C#. Founded by Eric Hexter and Jeffrey Palermo.
• CruiseControl.NET: CruiseControl.NET is an Automated Continuous Integration server, implemented using the Microsoft .NET Framework.
• S#arp Architecture: Pronounced “Sharp Architecture,” this is a solid architectural foundation for rapidly building maintainable web applications leveraging the ASP.NET MVC framework with NHibernate. The primary advantage to be sought in using any architectural framework is to decrease the code one has to write while increasing the quality of the end product. A framework should enable developers to spend little time on infrastructure details while allowing them to focus their attentions on the domain and user experience.
• Spark View Engine: Spark is a view engine for Asp.Net Mvc and Castle Project MonoRail frameworks. The idea is to allow the html to dominate the flow and the code to fit seamlessly.
• TortoiseSVN: A Subversion client, implemented as a windows shell extension. TortoiseSVN is a really easy to use Revision control / version control / source control software for Windows. Since it’s not an integration for a specific IDE you can use it with whatever development tools you like.
• Castle Windsor: Castle Project offers two Inversion of Control Containers. The MicroKernel and the Windsor Container. Castle Windsor aggregates the MicroKernel  and exposes a powerful configuration support. It is suitable for common enterprise application needs. It is able to register facilities and components based on the configuration and adds support for interceptors.

Take a look at these projects. I’m sure you’ll be able to find some good use for them in your projects!

Via .NET Zone.

Related posts:

1. Open Source Software
2. Unit testing
3. Persistance layer: object-relational mapping tools
4. Improving software quality: automatic testing
5. Parallel programming with .NET

So, what if I want to develop my own personal project and I require a RDBMS (Relational DataBase Management System)? Oracle and MS-SQL are out of the question because of their high cost. MS-SQL Express has great limitations, so, although it is free, we won’t be considering it for our purpose. Which is the best open source RDBMS?

Today’s most known open source RDBMS are MySQL and PostgreSQL. PostgreSQL is considered to beat MySQL in the features war. This used to be true some time ago, but it’s no longer the case anymore. 99% of the needs you will have with your RDBMS will be covered by both MySQL and PostgreSQL. Still, there’s many people who think that MySQL has improved a lot, but it’s just not PostgreSQL.

If you want to compare performance, fans of both systems will tell you their RDBMS is faster than the other one. On one hand, PostgreSQL has been recently paying attention to speed, and has been making its product faster and faster with every release. On the other hand, MySQL proponents say that, if configured properly, MySQL’s MyISAM tables are indeed lightweight and make for a faster database.

But probably, the most important thing to consider when choosing which RDBMS you should use, is which one is easier to use. I can tell you that previous Oracle experience will make you feel at home and comfortable with PostgreSQL. Still, the MySQL community seems to be much bigger than PostgreSQL’s, so, should you require some assistance when developing your project, if you’re using MySQL chances are that you will get quick help from them.

MySQL is licensed under the GNU GPL, but offers an alternative commercial license for those who don’t want to be restricted by that license. PostgreSQL uses the BSD license, which stipulates that the credits have to be maintained, but beyond that you can do whatever you want with it.

But, after all, it just all comes down to personal tastes. Just choose whatever you like and whichever you think might fit your needs better. What might be the best for one person, might be a bad choice for another.

Check these links for more info:

• Open Source Database Feature Comparison Matrix
• Comparison of RDBMS

Related posts:

1. Sluggish database view? Materialize it!
2. Entity Framework
3. Persistance layer: object-relational mapping tools
4. Creating a Timestamp column with Entity Framework

• Comment as much as needed, but no more: comment what you consider needed, but don’t tell others your life story. Too many comments may make some other developer get distracted from the actual code.
• Javascript is used to define the behaviour, not the look & feel: even though there’s the possibility to set the appearance of your application through JavaScript, you should leave that for CSS. Always follow the “separation of concerns” mantra. A change in the icons or the color of borders shouldn’t require dealing with JavaScript code.
• Modularize: keep your code modularized and specialized. Make sure to write smaller, generic helper functions that fulfill one specific task, rather than catch-all methods.
• Allow for configuration and translation: everything that is likely to change in your code should not be scattered throughout the code, for example, labels, CSS classes and IDs. By putting these into a configuration object and making it public, we make maintenance very easy and allow for customization.
• Access the DOM as little as possible: accessing the DOM in browsers is an expensive thing to do. The DOM is a very complex API and rendering in browsers can take up a lot of time. To make sure that your code is fast and doesn’t slow down the browser to a halt try to keep DOM access to a bare minimum.
• Build on the shoulders of giants: JavaScript libraries are specifically built to make browsers behave as you would expect by plugging browser holes. Therefore, if you want to write code that works without keeping the maintenance overhead of supporting current browsers and those to come, start with a good library.
• Development code is not live code: live code is done for machines, development code is done for humans. Make your code as readable and understandable as possible. Then, before deploying your web application, collate, minify and optimize your code in a build process.

If you follow all these recommendations, you can be sure you’ll have produced a high quality code that will be easy to maintain.

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3. Object Oriented JavaScript I: the basics