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Communicating between two Bounded Contexts in DDD

Asked 2013-05-23T11:42:58.960
41

I have few different Bounded Contexts in the domain. The validation of a CRUD operation is built in each Bounded Context.

For example, I can create an entity called GAME only if the person creating it is a Group Leader.

I have two Bounded Contexts (BC) in this example. One is the Game BC and the other is the User BC. To solve the problem, in the Game BC, I have to make a domain service call like IsGroupLeader() to the User BC before proceeding on creating the Game.

I don't think this type of communication is recommended by DDD. I can have a User entity also in the Game BC, but I don't want to because the same User entity is being used differently in a different context in a different BC.

My questions are:

  1. Should I use Domain events where the Game BC has to send an event to the User BC asking the status of the User? With this approach, I don't make a synchronous call like IsGroupLeader but an event called is_group_leader. Then the Game BC has to wait for the User BC to process the event and return the status. The Game BC will create the Game entity only after the User BC process the event.

  2. Is CQRS a solution to my problem?

Any idea appreciated.

domain-driven-design cqrs domain-events bounded-contexts
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Here is how I would reason about it.

I would argue that the Game BC doesn't know about "Users", it might however know about "Players".

If the Game BC is dependant on an active/current player then it should be passed into the BC when creating the Game BC instance.

eg.

 Player currentPlayer = GetPlayerSomehow...();
 GameBC gameBC = new GameBC(currentPlayer);
 gameBC.DoStuff();

Now your two BC's are still separate, you can test them separately etc.

And to make it all work you simply do something like:

 User currentUser = GetCurrentUser();
 Player currentPlayer = new Player();
 currentPlayer.IsGroupLeader = currentUser.IsGroupLeader;
 GameBC gameBC = new GameBC(currentPlayer);
 gameBC.DoStuff();

This serves as an anticorruption layer between the UserBC and the GameBC, you can move and validate the state you want from the UserBC into the state you need for your GameBC.

And if your GameBC needs to access many users, you can still pass some sort of mapping service into the game BC that does this kind of transformation internally.

answered 2013-05-24T07:47:54.067

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