About

Lokad Contracts DSL is an optional console utility that you can run in the background. It tracks changes to files with special compact syntax and updates CS file with message contract definitions.

Changes are immediate upon saving file (and ReSharper immediately picks them). This is an improved version of Lokad Code DSL, it supports identities and can auto-generate interfaces for aggregates and aggregate state classes.

Was:

AddSecurityPassword?(SecurityId id, string displayName, string login, string password)

Becomes:

[DataContract(Namespace = "Sample")]
public partial class AddSecurityPassword : ICommand<SecurityId>
{
    [DataMember(Order = 1)] public SecurityId Id { get; private set; }
    [DataMember(Order = 2)] public string DisplayName { get; private set; }
    [DataMember(Order = 3)] public string Login { get; private set; }
    [DataMember(Order = 4)] public string Password { get; private set; }
 
    AddSecurityPassword () {}
    public AddSecurityPassword (SecurityId id, string displayName, string login, string password)
    {
        Id = id;
        DisplayName = displayName;
        Login = login;
        Password = password;
    }
}

Lokad Code DSL is used by Lokad.CQRS (was originally part of it) and is explained in greater detail in BeingTheWorst Podcast - Episode 12.

You can try this out by starting Sample project and then changing Sample\Contracts.ddd (view [Contracts.ddd source] (http://github.com/Lokad/lokad-codedsl/blob/master/Sample/Contracts.ddd)). Code DSL tool will be regenerating corresponding contracts file as you change and save (view Contracts.cs source).

Current DSL code generates contracts classes that are compatible with DataContracts, ServiceStack.JSON and ProtoBuf.

You can get download binary from github downloads. Sometimes even later stable version would be available by getting latest source code and building.

Lokad Code DSL (homepage) is shared as open source project by Lokad in hopes that it would benefit the community.

Syntax Definitions

Namespaces

Add namespace for our messages

namespace NameSpace

Result:

namespace NameSpace  
{  
...  
}

Data contract namespace

extern "Lokad"

Result:

[DataContract(Namespace = "Lokad")]

Simple Contract definitions

Universe(UniverseId Id, string name)

Result:

[DataContract(Namespace = "Lokad")]
public partial class Universe
{
    [DataMember(Order = 1)] public UniverseId Id { get; private set; }
    [DataMember(Order = 2)] public string Name { get; private set; }

    Universe () {}
    public Universe (UniverseId id, string name)
    {
        Id = id;
        Name = name;
    }
}

Interface Shortcuts

In order to use interface in contract classes, need to create interface shortcut first, definition of interface IIdentity must be contained in C# file

if ! = IIdentity

For the next step define simple class with one property

UniverseId!(long id)

Result:

[DataContract(Namespace = "Lokad")]
public partial class UniverseId : IIdentity
{
    [DataMember(Order = 1)] public long Id { get; private set; }
    
    UniverseId () {}
    public UniverseId (long id)
    {
        Id = id;
    }
}

Method Argument Constants

Method arguments constants allow us to define constant to replace method argument definition. For example, now we can use term dateUtc instead full definition with argument type and name.

const dateUtc = DateTime dateUtc

Application service & state

Definition of application service must begining with interface key.

interface Universe(UniverseId Id)
{
    // define shortcut for commands
    if ? = IUniverseCommand
    // define shortcut for events
    if ! = IUniverseEvent<UniverseId>

    CreateUniverse?(name)
        // override ToString() for command
        explicit "Create universe - {name}"
        UniverseCreated!(name)
        // override ToString() for event
        explicit "Universe {name} created"
}

Result:

public interface IUniverseApplicationService
{
    void When(CreateUniverse c);
}

public interface IUniverseState
{
    void When(UniverseCreated e);
}

Command and corresponding event

[DataContract(Namespace = "Lokad")]
public partial class CreateUniverse : IUniverseCommand
{
    [DataMember(Order = 1)] public UniverseId Id { get; private set; }
    [DataMember(Order = 2)] public string Name { get; private set; }
    
    CreateUniverse () {}
    public CreateUniverse (UniverseId id, string name)
    {
        Id = id;
        Name = name;
    }
    
    public override string ToString()
    {
        return string.Format(@"Create universe - {0}", Name);
    }
}

[DataContract(Namespace = "Lokad")]
public partial class UniverseCreated : IUniverseEvent<UniverseId>
{
    [DataMember(Order = 1)] public UniverseId Id { get; private set; }
    [DataMember(Order = 2)] public string Name { get; private set; }
    
    UniverseCreated () {}
    public UniverseCreated (UniverseId id, string name)
    {
        Id = id;
        Name = name;
    }
    
    public override string ToString()
    {
        return string.Format(@"Universe {0} created", Name);
    }
}

Syntax Highlights

Syntax used in the DSL tool is derived from keywords in C++ and C#. This means, that any text editor could provide nice highlighting, if you use language color settings from C++ or C#.

Here's how DSL source code might look like:

Sublime Text 2	Visual Studio 2010

Visual Studio 2010 settings

Here are the settings to set up in Visual Studio:

![Visual Studio settings] (https://github.com/Lokad/lokad-codedsl/raw/master/Docs/vs2010_settings.PNG)

Related articles

• Tutorial: Extending Lokad DSL Tool by Vidar Løvbrekke Sømme
• [Improved DSL Syntax for DDD and Event Sourcing] (http://abdullin.com/journal/2012/7/25/improved-dsl-syntax-for-ddd-and-event-sourcing.html)

Feedback

Please, feel free to drop feedback in the Lokad Community.