Marcin Obel» .Net Framework

C# 4.0 Named Arguments – example usage

Marcin Obel — Tue, 24 Aug 2010 18:06:57 +0000

One of the new features introduced in C# 4.0 were named arguments. There was a lot of discussion in the Internet about them and theirs pros and cons. Of course named arguments can be abused like any other part of C# but I think that when used wisely are able to make your code more readable and easier to understand without the knowledge what is hidden behind the scene. Few days ago I was working on integration tests for REST API exposed by a startup I am working on with my team. Each test required some “execution context” and a way to inform “infrastructure” that after execution whole environment should be cleaned up (e.g. database). Because I use NUnit as a runner the first idea that came to my mind was to utilize [SetUp] and [TearDown] methods. But after some prototyping I realized that the solution is hard to understand and obfuscates the tests. Next day after short chat with @lesnikowski new idea popped into my mind: I can create “execution context” with lambdas and named arguments! The example below shows how I have changed the idea into real code.

[Test]
public void Add_WhenInvokedShouldAddNewExternalAudioFolder()
{
    Execute(test: () =>
    {
        var json = WebApiClient.ExternalAudioFolder.Add("My folder", "My description");
        var message = json.DeserializeJson();

        Assert.That(message.Result, Is.EqualTo(Message.Success));
    },
    inContextOf: Account.Basic,
    cleanUpAfter: true);
}

What do you think about the code above? Do you have any additional ideas how to improve readability of this “execution context”?

Fluent NHibernate conventions II – example for enumerations

Marcin Obel — Thu, 20 May 2010 14:25:36 +0000

Most of the time I do not have to touch Fluent NHibernate conventions I have created some time ago. But from time to time I find in mappings some common scenario which is a good candidate to become a convention. This time I found that every time I am mapping a property of enumeration type I have to specify its length manually.

Because I hate redundant work I have defined a Fluent NHibernate convention presented below.

using System;
using System.Linq;
using FluentNHibernate.Conventions;
using FluentNHibernate.Conventions.AcceptanceCriteria;
using FluentNHibernate.Conventions.Inspections;
using FluentNHibernate.Conventions.Instances;

namespace ExampleConventions
{
    public class EnumColumnLengthConvention
        : IPropertyConvention, IPropertyConventionAcceptance
    {
        public void Accept(IAcceptanceCriteria criteria)
        {
            criteria.Expect(x => x.Property.PropertyType.IsEnum)
                .Expect(x => x.Length == 0);
        }

        public void Apply(IPropertyInstance instance)
        {
            var names = Enum.GetNames(instance.Property.PropertyType);
            instance.Length(names.Max(name => name.Length));
        }
    }
}

The convention is really simple. Its whole logic can be found in Apply method and I think it is self explanatory so there is nothing to describe here.

IronRuby/RHTML based templates for .NET

Marcin Obel — Mon, 07 Dec 2009 23:09:20 +0000

During last few days I was prototyping some of new features I would like to add to ByteCarrot application. One of them is new template engine which will replace current XSLT based solution. I wanted something with more friendly syntax, something easy to create, change and maintain. I took a look at many template engines available for .NET platform but none of them met my needs. I thought that it would be nice to have solution with scripting support and syntax similar to this available in default ASP.NET MVC view engine.

After digging I have found an ASP.NET MVC application prototype with view engine based on IronRuby. It was created by Phil Haack‘s team and its syntax was exactly the same as RHTML used in Ruby on Rails views. It turned out that this engine was exactly what I needed, so I have taken parts of the code and adapted it to my scenario. The result is amazing because now I have fully functional templates engine with support of dynamic language where I can handle every possible HTML generation scenario.

As an attachment to this post I have added the code created during prototyping. The code contains few classes where the most important is RhtmlEngine. It has very simple, self-expanatory interface and acts as an “entry point” for using mentioned templates engine. Below you can find two samples showing capabilities of my solution but if you want to take a look at the implementation and make your hands dirty feel free to download the code and play with it for yourself.

public class RhtmlEngine
{
    public Result Render(object model, string temlateFile, string targetFile)
        ...
    public Result Render(object model, StreamReader rhtml, StreamWriter writer)
        ...
}

Simple template

The templates engine requires three things to be able to generate HTML:

Model representing the data which should be presented in form of HTML page,
Template defining how model should be presented,
Target where generated HTML page should be saved.

Listing below shows simple template generating a header and a list of hobbies. Notice that IronRuby blocks are embedded exactly the same as Visual Basic .NET or C# code is embedded in ASP.NET MVC views.

SimpleTemplate.rhtml


    
        Hi! My name is: <%= model.FirstName %><%= model.LastName %>
        I like:
        
        <% model.Hobbies.each do |hobby| %>
			<%= hobby %>
        <% end %>

Template shown above can be used to generate an HTML representation of the following model:

var model = new SampleModel
{
    FirstName = "Marcin",
    LastName = "Obel",
    Hobbies = new List
    {
        "yachting",
        "fishing",
        "cycling"
    }
};

As you can notice looking at listing below, because the templates engine is very simple, you need only one line to change the model into HTML page.

var result = new RhtmlEngine().Render(model, "SimpleTemplate.rhtml", "SimpleHtml.html");

In result (as shown below) the code above will produce clean HTML filled in with the data from model.

SimpleHtml.html


    
        Hi! My name is: MarcinObel
        I like:
        
            yachting
            fishing
            cycling

More advanced example

The example above does not show the most powerful part of this solution which is in fact inherited from IronRuby itself. Because templates are based on fully functional, dynamic language there is a possibility to extend basic features like loops and if statements (available in all templates engines) with things like functions, classes or even use some functionalities available in .NET Framework. Next example extends this one mentioned in previous section. In the listing below you can notice two new functions:

encode - uses HttpUtility class from .NET Framework to encode HTML code
render_li – renders an item of HTML list

AdvancedTemplate.rhtml

<%
require 'System.Web, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'
include System::Web

def encode(text)
    HttpUtility.HtmlEncode(text)
end

def render_li(text)
    writer.Write "#{text}";
end
%>


    
        Hi! My name is: <%= model.FirstName %><%= model.LastName %>
        I like:
        
        <% model.Hobbies.each do |hobby|
                 render_li hobby
             end %>
        
                    <%= encode model.UglyJavaScript %>

In order to present a usage of custom IronRuby function added to the template, below you can find extended model from previous example. Now the model contains additional property named UglyJavaScript containing JavaScript code which should be encoded before it can be presented in HTML.

var model = new SampleModel
{
    FirstName = "Marcin",
    LastName = "Obel",
    Hobbies = new List
    {
        "yachting",
        "fishing",
        "cycling"
    },
    UglyJavaScript = @""
};

var result = new RhtmlEngine().Render(model, "AdvancedTemplate.rhtml", "AdvancedHtml.html");

Like in previous example after passing the model and the template into engine we receive an HTML. This time as you can see it contains JavaScript code from model encoded using .NET Framework functionality in order to be able to display it.


    
        Hi! My name is: MarcinObel
        I like:
        
        yachting
fishing
cycling
        
                <script type='text/javascript'>window.close();</script>

Resources

Fluent NHibernate conventions – examples

Marcin Obel — Thu, 26 Nov 2009 22:22:59 +0000

Fluent NHibernate is my favorite extension for NHibernate. I am using it since early betas and I have to say that I love it. One of its underestimated features are conventions. I decided to extract some of them from one of my projects and provide real life examples how they can be used. My conventions are listed below but if you need more information visit Fluent NHibernate Wiki where this feature is described in detail.

ColumnNullabilityConvention – says that if nullability for column has not been specified explicitly, should be set to “NOT NULL”.

public class ColumnNullabilityConvention
    : IPropertyConvention, IPropertyConventionAcceptance
{
    public void Accept(IAcceptanceCriteria criteria)
    {
        criteria.Expect(x => x.Nullable, Is.Not.Set);
    }

    public void Apply(IPropertyInstance instance)
    {
        instance.Not.Nullable();
    }
}

CreatedAtPropertyAccessConvention – says that every property named CreatedAt should be accessed through camel case field hidden behind it.

public class CreatedAtPropertyAccessConvention
    : IPropertyConvention, IPropertyConventionAcceptance
{
    public void Accept(IAcceptanceCriteria criteria)
    {
        criteria.Expect(x => x.Property.Name == "CreatedAt");
    }

    public void Apply(IPropertyInstance instance)
    {
        instance.Access.ReadOnlyPropertyThroughCamelCaseField(
            CamelCasePrefix.Underscore);
    }
}

ForeignKeyConstraintNameConvention – says that name of every foreign key constraint representing one to many relation should consist of names of entities for which it was specified.

public class ForeignKeyConstraintNameConvention
    : IHasManyConvention
{
    public void Apply(IOneToManyCollectionInstance instance)
    {
        instance.Key.ForeignKey("{0}_{1}_FK".AsFormat(
        instance.Member.Name, instance.EntityType.Name));
    }
}

ForeignKeyNameConvention – says that name of every column containing foreign key id should consist of name of type which it points to with “Id” suffix.

public class ForeignKeyNameConvention : IHasManyConvention
{
    public void Apply(IOneToManyCollectionInstance instance)
    {
        instance.Key.Column(instance.EntityType.Name + "Id");
    }
}

PrimaryKeyNameConvention - says that name of every column representing primary key should consist of entity name and “Id” suffix.

public class PrimaryKeyNameConvention : IIdConvention
{
    public void Apply(IIdentityInstance instance)
    {
        instance.Column(instance.EntityType.Name + "Id");
    }
}

ReferenceConvention – says that name of column referenced in many to one convention should consist of entity name and “Id” suffix.

public class ReferenceConvention : IReferenceConvention
{
    public void Apply(IManyToOneInstance instance)
    {
        instance.Column(instance.Property.PropertyType.Name + "Id");
    }
}

StringColumnLengthConvention – says that if length for string column has not been specified, it should be set to 100.

public class StringColumnLengthConvention
    : IPropertyConvention, IPropertyConventionAcceptance
{
    public void Accept(IAcceptanceCriteria criteria)
    {
        criteria.Expect(x => x.Type == typeof(string))
            .Expect(x => x.Length == 0);
    }

    public void Apply(IPropertyInstance instance)
    {
        instance.Length(100);
    }
}

TableNameConvention – says that if name for table has not been specified, it should be created using concatenation of entity name and “s” suffix.

public class TableNameConvention
    : IClassConvention, IClassConventionAcceptance
{
    public void Accept(IAcceptanceCriteria criteria)
    {
        criteria.Expect(x => x.TableName, Is.Not.Set);
    }

    public void Apply(IClassInstance instance)
    {
        instance.Table(instance.EntityType.Name + "s");
    }
}

At the end the most important thing which shows that such conventions make sense. With default Fluent NHibernate conventions DDL generated by NHibernate for MySQL looked like this:

alter table `Athlete`  drop foreign key FK9221C9B94070A6F0

drop table if exists Countries

drop table if exists `Athlete`

create table Countries (
     Id INTEGER NOT NULL AUTO_INCREMENT,
     Name VARCHAR(255),
     primary key (Id)
)

create table `Athlete` (
     Id INTEGER NOT NULL AUTO_INCREMENT,
     DisplayName VARCHAR(255),
     Email VARCHAR(255),
     Password VARCHAR(255),
     CreatedAt DATETIME,
     IsActive TINYINT(1),
     Country_id INTEGER,
     primary key (Id)
)

alter table `Athlete`
	add index (Country_id),
	add constraint FK9221C9B94070A6F0
	foreign key (Country_id)
	references Countries (Id)

When I have applied conventions mentioned above to my fluent mappings DDL looks like this:

alter table Athletes  drop foreign key Athletes_Country_FK

drop table if exists Athletes

drop table if exists Countries

create table Athletes (
     AthleteId INTEGER NOT NULL AUTO_INCREMENT,
     DisplayName VARCHAR(100) not null,
     Email VARCHAR(100) not null,
     Password VARCHAR(100) not null,
     CreatedAt DATETIME not null,
     IsActive TINYINT(1) not null,
     CountryId INTEGER,
     primary key (AthleteId)
)

create table Countries (
     CountryId INTEGER NOT NULL AUTO_INCREMENT,
     Name VARCHAR(100) not null,
     primary key (CountryId)
)

alter table Athletes
	add index (CountryId),
	add constraint Athletes_Country_FK
	foreign key (CountryId)
	references Countries (CountryId)

For me it looks much better. Additionally I have made it once and that is it. Now I have to care only about domain model and business logic without thinking about not so important stuff lake names of database objects.

MSpec BDD framework installer

Marcin Obel — Mon, 23 Nov 2009 11:23:35 +0000

Installation of MSpec BDD framework from source code is quite annoying. With each release you have to deploy everything manually one more time what in fact is hard to accept in 21th century. I know that work on Open Source project requires a lot of time (I have my own project called ByteCarrot) and you cannot do everything. Because of that I decided to help a little bit creators of MSpec and I have prepared an installer for this BDD framework. It is based on WiX and latest release of MSpec witch is version 0.3.

The installer is able to automatically integrate MSpec with TestDriven.NET and ReSharper (4.1, 4.5, 5.0). This is first version of the installer and of course like always there can be some bugs so please let me know if you find something.

Download installer for MSpec 0.3

Rake in .NET projects – installation and setup

Marcin Obel — Wed, 18 Nov 2009 18:10:27 +0000

Recently I have rewritten all MSBuild scripts which I used in ByteCarrot project to Rake. I made the decision about changing build solution mostly because I required something what works not only under Windows but also on other operating systems. After rewriting turned out that Rake is a great solution for tasks for which it was created and can be used not only with Ruby/RoR projects but also with other technologies like .NET and Mono. It is really awesome multi-purpose tool. Today I would like to show you how to install and configure Rake on Windows operating system in order to start using it in your projects.

Ruby installation

First of all, because Rake is based on Ruby language, you will need an interpreter. You can download Ruby distribution from its official website but I do not recommend that because there is only installer for version 1.8.6 which is quite old. Other packages for Windows on this website are in a form of compressed archives and do not contain some additional, required libraries. In my opinion the best option is to download one of preview version of installer for Ruby 1.9.1-p129 (rubyinstaller-1.9.1-p129-preview1.exe) available on RubyForge.

When the installer is on your hard drive, start installation. There is nothing magic in the installation process but you should remember that Rake does not work properly when Ruby in installed in C:\Program Files directory (probably because of space in the path). Because of that leave the default installation path or change it to something without spaces like for example C:\Ruby.

Last thing you should do to be able to use Ruby is adding the location of its binaries to the %Path% environment variable. In my case this variable was extended with C:\Ruby\bin path.

Now you can check if everything works by executing from command line two following commands:

ruby –v
gem -v

The output from console should be:

C:\>ruby –v
ruby 1.9.1p129 (2009-05-12 revision 23412) [i386-mingw32]
C:\>gem –v
1.3.4

Rake installation

Now, when Ruby is installed and you are sure that it works you can take care of Rake. The most popular and safe way to install Ruby extensions and libraries (including Rake) is mechanism called Gems. In order to install Rake using Gems execute following command from command line:

C:\>gem install --remote rake

The output from console should be:

C:\>gem install --remote rake
Successfully installed rake-0.8.7
1 gem installed
Installing ri documentation for rake-0.8.7...
Updating class cache with 0 classes...
Installing RDoc documentation for rake-0.8.7...

When the command will finish do not close command line window yet. At the end execute one more command to be sure that Rake is installed properly:

C:\>rake –V

The output from console should be:

C:\>rake –V
rake, version 0.8.3

Congratulations! You have managed to install Rake and you are ready to write your first build script. More about Rake can be found on official site of the project. Example Rake scripts can be found in ByteCarrot source code on CodePlex.

ASP.NET MVC 2 Beta – new features

Marcin Obel — Wed, 18 Nov 2009 12:38:57 +0000

Yesterday at PDC 09 Bob Muglia announced the release of ASP.NET MVC 2 Beta. This release contains a lot of new, interesting stuff. Below you can find a list of new features taken from official release notes.

New RenderAction method

Html.RenderAction (and its counterpart Html.Action) is an HTML helper method that calls into an action method from within a view and renders the output of the action method in place. Html.RenderAction writes directly to the response, whereas Html.Action returns a string with the output. RenderAction works only with actions that render views.

Strongly typed UI helpers

ASP.NET MVC 2 includes new expression-based versions of existing HTML helper methods. The new helpers include the following:

ValidationMessageFor
TextAreaFor
TextBoxFor
HiddenFor
DropDownListFor

TempDataDictionary improvements

The behavior of the TempDataDictionary class has been changed slightly to address scenarios where temp data was either removed prematurely or persisted longer than necessary. For example, in cases where temp data was read in the same request in which it was set, the temp data was persisting for the next request even though the intent was to remove it. In other cases, temp data was not persisted across multiple consecutive redirects.

To address these scenarios, the TempDataDictionary class was changed so that all the keys survive indefinitely until the key is read from the TempDataDictionary object. The Keep method was added to TempDataDictionary to let you indicate that the value should not be removed after reading. The RedirectToActionResult is an example where the Keep method is called in order to retain all the keys for the next request.

Client validation library

MicrosoftMvcAjax.js now includes a client-side validation library that is used to provide client validation for models in ASP.NET MVC. To enable client validation, include the following two scripts in your view.

MicrosoftAjax.js
MicrosoftMvcAjax.js

The following example shows a view with client validation enabled.




<% Html.EnableClientValidation(); %>
<% using(Html.BeginForm()) { %>
  //...
<% } %>

“Add Area” dialog box

ASP.NET MVC 2 Beta includes a new Add Area context menu item when you right-click either the root project node or the Areas folder (if one exists). If a root Areas folder does not already exist, the command creates one, and it then creates the files and folders for the area that you specify.

Calling action methods asynchronously

The AsyncController class is a base class for controllers that enables action methods to be called asynchronously. This lets an action method call external services such as a Web service without blocking the current thread. For more information, see Using an Asynchronous Controller in ASP.NET MVC In the ASP.NET MVC 2 documentation.

Blank project template

In response to customer feedback, an empty ASP.NET MVC project template is now included with ASP.NET MVC 2 Beta. This empty project template contains a minimal set of files used to build a new ASP.NET MVC project.

Multiple model validator providers

ASP.NET MVC 2 Beta lets you register multiple validation providers. The following example shows how to register multiple providers.

protected void Application_Start() {
    ModelValidatorProviders.Providers.Add(new MyXmlModelValidatorProvider());
    ModelValidatorProviders.Providers.Add(new MyDbModelValidatorProvider());
    //...
}

Multiple value provider registration

In ASP.NET MVC 2 Beta, the single value provider that was available in ASP.NET MVC 1.0 has been split into multiple value providers, one for each source of request data. The new value providers include the following:

FormValueProvider
RouteDataValueProvider
QueryStringValueProvider
HttpFileCollectionValueProvider

These value providers are registered by default. You can register additional value providers that pull data from other sources. The following example shows how to register additional value providers in the in Global.asax file.

protected void Application_Start() {
    ValueProviders.Providers.Add(new JsonValueProvider());
    //...
}

Download full ASP.NET MVC 2 Beta Release Notes

My favorite System.String extension methods

Marcin Obel — Sun, 27 Sep 2009 15:47:26 +0000

Each business applications developer spends a lot of the time working with strings. Strings are everywhere and we do not avoid that, but we can make our life simpler. How many times each day do you use String.Format(), String.Trim() or String.IsNullOrEmpty()? This are of course very helpful method but turned out that in my case they do not provide a functionality I require. I found out that almost all the time I am treating null, an empty string and a string with whitespaces only as the same “undefined/unkown” value. I am doing that mostly with strings received from outside of my applications where I an interested in “real values” instead of for instance a string with spaces only. In this case, methods mentioned above do not meet my needs. Because of that I have created replacement for them as an extension methods and they became my favorite tools to work with strings (I am using them everywhere instead of out of the box methods).

StringExtensions class defining extension methods:

using System;

namespace ByteCarrot.Shared.Infrastructure
{
    public static class StringExtensions
    {
        public static string NullTrim(this string s)
        {
            if (s == null)
            {
                return null;
            }

            s = s.Trim();
            return s == String.Empty ? null : s;
        }

        public static bool IsSet(this string s)
        {
            return s.NullTrim() != null;
        }

        public static string AsFormat(
            this string s, params object[] args)
        {
            return String.Format(s, args);
        }
    }
}

IsSet() extension method – returns true only if string contains at least one “printable” character:

if (!this.Commands.IsSet())
{
    this.Logger.LogError("Commands not specified.");
}

NullTrim() extension method – returns string trimmed from both sides and null when base string was null or after trimming turned out that output is an empty string:

var commands = this.Commands.NullTrim();

AsFormat() extension method – shorter replacement for System.String:

Resources.RequiredField.AsFormat("First name");

It is nothing fancy but make my life easier.