Fluency is a framework for building fluent interfaces or DSLs in .NET. It simplifies building fluent interfaces for configuration, but also has facilities for creating interfaces to build anonymous (random) test data for integration tests.

The FluencyKoans project is good way to learn how to use Fluency. It is a progression of short code exercises to introduce you to Fluency.

You can see upcoming features and work in progress at the Fluency Trello Board.

You can install Fluency either by:

1. Using the NuGet package manager for Visual Studio typing Install-Package Fluency at the package manager console or searching for "Fluency" in the UI, or
2. Downloading the latest binaries from the Fluency GitHub repository by clicking the "Downloads" button.

There are two ways to use Fluency.

1. Use the standard dynamic builder by creating of instance of DynamicFluentBuilder<T> where T is the target type to build.
2. Use a custom builder by subclassing FluentBuilder<T> and creating the methods/properties you want in your fluent interface.

Let's say you want a fluent interface to build the follwing configuration class.

	public class MyConfiguration
	{
	    public string UserName { get; set; }
	    public bool AllowLogin { get; set; }
	    public int TimeoutMinutes { get; set; }
	}

###Using the Dynamic Builder

This is the simplest way to use Fluency. You simply (1) instantiate DynamicFluentBuilder<T> for your type, then (2) call the lambda-based config methods to set the values, and finally (3) call build() to build the resulting config.

	MyConfiguration config = 
	    new DynamicFluentBuilder<MyConfiguration>()
	        .For( x => x.UserName, "Bob" )
	        .With( x => x.AllowLogin, true )
	        .Having( x => x.TimeoutMinutes, 5 )
	        .build();

###Using a Custom Builder

Using a custom builder gives you full control of the fluent interface. To create a custom builder, you need to subclass FluentBuilder<T> and implement your fluent interface.

	public class MyConfigurationBuilder : FluentBuilder< MyConfiguration >
	{
	    public MyConfigurationBuilder ForUser( string userName )
		{
			SetProperty( x => x.UserName, userName );
			return this;
		}
		
		public MyConfigurationBuilder IsAllowedToLogin()
		{
			SetProperty( x => x.AllowLogin, true );
			return this;
		}
		
		public MyConfigurationBuilder IsNotAllowedToLogin()
		{
			SetProperty( x => x.AllowLogin, false );
			return this;
		}
		
		public MyConfigurationBuilder MinutesBeforeTimeout( int timeoutMinutes )
		{
			SetProperty( x => x.TimeoutMinutes, timeoutMinutes );
			return this;
		}
	}

And here is how you would use the builder.

	MyConfiguration config =
		new MyConfigurationBuilder()
			.ForUser( "Bob" )
			.IsAllowedToLogin()
			.MinutesBeforeTimeout( 20 )
			.build();

While the custom builder requires more work to create, it gives you much more control over the interface and doesn't require the user to know the structure of the class being built.

I don't know about you, but the "new" keyword and the builder's class name really muddle the code up. If I am creating these objects directly, I often create a helper class to create the builders.

	public static class a
	{
		public static MyConfigurationBuilder Config 
		{
			get { return new MyConfigurationBuilder(); }
		}
	}

Now my syntax to create the builder looks like this

	var config = a.Config
					.ForUser( "Bob" )
					.IsAllowedToLogin()
					.MinutesBeforeTimeout( 20 )
					.build();

I wanted to introduce this since I will be using this syntax going forward to simplify the code.

Nesting builders greatly simplifies building object graphs and creating a more expressive fluent interface.

###By Passing a Builder Parameter

Here's an example that just passes a builder for the nested object.

	var config = a.Config
					.ForUser( a.User.FirstName( "Bob" )
									.LastName( "Smith " )
									.UserName( "bsmith" ) 
							)
					.MinutesBeforeTimeout( 20 )
					.build();

To do this, MyConfiguration would need a User property, we would create aUserBuilder. Then we modify the MyConfigurationBuilder.ForUser() method to accept a parameter of type UserBuilder:

	public MyConfigurationBuilder ForUser( UserBuilder userBuilder )
	{
		SetProperty( x => x.User, userBuilder );
		return this;
	}

When using the SetProperty() method for reference types, it will accept either an instance of the type (i.e. SetProperty( x => x.User, new User() )), or a builder for that type (as we see above). If a builder is passed in, it will be built whenever build() is called on this builder.

###By Exposing a Builder Through an Action Parameter

An alternative approach would be to accept an action as the parameter for the ForUser() method. This gives you the following.

	var config = a.Config
					.ForUser( u => u.FirstName( "Bob" )
									.LastName( "Smith " )
									.UserName( "bsmith" ) 
							)
					.MinutesBeforeTimeout( 20 )
					.build();

In this case, the ForUser() method would look like so:

	public MyConfigurationBuilder ForUser( Action< UserBuilder > userBuilderAction )
	{
		var userBuilder = new UserBuilder();
		userBuilderAction( userBuilder );
		SetProperty( x => x.User, userBuilder );
		return this;
	}

Fluency allows you to configure the default values that we be built for each property if no value is provided through the fluent interface. To do this, simply set those values using SetProperty() in the constructor of your builder.

	public class MyConfigurationBuilder : FluentBuilder< MyConfiguration >
	{
		public MyConfigurationBuilder()
		{
			// Setup defaults.
			SetProperty( x => x.AllowLogin, false );
			SetProperty( x => x.TimeoutMinutes, 5 );
		}
	}

Your default values can also include defaults for nested builders as well, which would ensure that sub-objects get built even if the user didn't specify values for it while calling the fluent interface. This turns out to be a very powerful feature when you are tyring to build test data for integration tests.

Anonymous objects are simply objects with random (but valid) data. Fluency contains an extensive random value generator for all types of data. Check out this example.

	public class UserBuilder : FluentBuilder< User >
	{
		public UserBuilder()
		{
			SetProperty( x => x.FirstName, ARandom.FirstName() );
			SetProperty( x => x.LastName, ARandom.LastName() );
			SetProperty( x => x.Phone, ARandom.StringPattern( "(999) 999-9999" );
			SetProperty( x => x.City, ARandom.City() );
			SetProperty( x => x.State, ARandom.State() );
			SetProperty( x => x.Zip, ARandom.ZipCode() );
			
			var birthDate = ARandom.BirthDate();
			SetProperty( x => x.BirthDate, birthDate );
			SetProperty( x => x.FirstLoginDate, ARandom.DateTimeInPastSince( birthDate ) );			
		}
	}

If I added this builder to the a static class I created above, the syntax to create a valid anonymous user would be:

	var user = a.User.build();

When you add the ability to nest objects, you can see how it would be easy to generate a large object graph of test data very quickly. This greatly increases the readability of your tests because you don't see all the unnecessary details about the random data in your test...you only see the values that directly affect your test. For instance:

	[Test]
	public void A_user_under_18_should_not_be_allowed_access()
	{
		var service = new SomeAuthenticationServiceWeAreTesting();
		
		var userUnder18 = a.User.WhoseAgeIs( 5 ).build();
		
		Assert.That( service.AuthenticateUser( userUnder18 ), Is.False() );
	}

This assumes we add the method WhoseAgeIs() to the UserBuilder like so...

	public UserBuilder WhoseAgeIs( int age )
	{
		SetProperty( x => x.BirthDate, age.YearsAgo() ); // YearsAgo is an exension method on int.
		return this;
	}

I hope this gives you a little taste as to what Fluency can do. I have been using it over a year and have found it invaluable in my unit and integration testing.