src/site/apt/example_interceptors.apt

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 Using interceptors
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Using interceptors

 As of version 2.2, MetaModel has introduced an interceptor mechanism which allows you to add code to
 your DataContext that will be invoked before or after certain operations.
 
 The interceptors are implemented as a decorating, logical DataContext around your physical DataContext.
 In the graph below the 5 types of interceptors are depicted:

[interceptors.png] Modules in MetaModel

 To get a handle for an interceptable DataContext, use
 the {{{./apidocs/org/eobjects/metamodel/intercept/Interceptors.html} Interceptors}}.intercept(...) method.

 To apply an interceptor, implement one of the five interfaces:

 * QueryInterceptor: To intercept queries before they are executed.

 * DataSetInterceptor: To intercept datasets before they are returned.
 
 * TableCreationInterceptor: To intercept "create table" operations before they are executed.
 
 * RowInsertionInterceptor: To intercept "insert into" operations before they are executed.
 
 * SchemaInterceptor: To intercept schemas before they are returned.
 
 Once you've implemented your interceptor, for instance a QueryInterceptor, add it to an InterceptableDataContext, like this:
 
+-------------------------------+
public DataContext addMyInterceptor(DataContext dc) {
  InterceptableDataContext interceptableDataContext = Interceptors.intercept(dc);
  interceptableDataContext.addQueryInterceptor(new MyQueryInterceptor());
  return interceptableDataContext;
}
+-------------------------------+

 The important part about this code snippet is, that it returns the InterceptableDataContext instance. 
 Since this is itself also an implementation of the DataContext interface, you should be able to use this
 throughout your code without modifications.