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Writing Code to Customise a Domain-Specific Language

This section shows you how to use custom code to access, modify, or create a model in a domain-specific language.

There are several contexts in which you can write code that works with a DSL:

Instances of the classes that you define in DslDefinition.dsl are kept in a data structure called the In-Memory Store (IMS) or Store. The classes you define in a DSL always take a Store as an argument to the constructor. For example, if your DSL defines a class called Example:

Example element = new Example (theStore);

keeping objects in the Store (instead of just as ordinary objects) provides several benefits.

  • Transactions. You can group a series of related changes into a transaction:

    using (Transaction t = store.TransactionManager.BeginTransaction("updates"))

    {

    // make several changes to Store elements here

    t.Commit();

    }

    If an exception occurs during the changes, so that the final Commit() is not performed, the Store will be reset to its previous state. This helps you to make sure that errors do not leave the model in an inconsistent state. For more information, see Navigating and Updating a Model in Program Code.

  • Binary relationships. If you define a relationship between two classes, instances at both ends have a property that navigates to the other end. The two ends are always synchronized. For example, if you define a parenthood relationship with roles named Parents and Children, you could write:

    John.Children.Add(Mary)

    Both of the following expressions are now true:

    John.Children.Contains(Mary)

    Mary.Parents.Contains(John)

    You could also achieve the same effect by writing:

    Mary.Parents.Add(John)

    For more information, see Navigating and Updating a Model in Program Code.

  • Rules and Events. You can define rules that fire whenever specified changes are made. Rules are used, for example, to keep shapes on the diagram up to date with the model elements they present. For more information, see Responding to and Propagating Changes.

  • Serialization. The Store provides a standard way to serialize the objects it contains to a file. You can customize the rules for serializing and deserializing. For more information, see Customizing File Storage and XML Serialization.

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