9.3. Delegating Translator

In some instances, you may wish to extend multiple translators with the same functionality. Rather than create separate subclasses for each extension, functionality that is common to multiple extensions can be added to a subclass of BaseDelegatingExecutionFactory. Within this subclass, delegation methods can be overridden to perform the common functionality.

@Translator(name="custom-delegator")
public class MyTranslator extends BaseDelegatingExecutionFactory<Object, Object> {
        
        @Override
        public Execution createExecution(Command command,
                        ExecutionContext executionContext, RuntimeMetadata metadata,
                        Object connection) throws TranslatorException {
                if (command instanceof Select) {
                        //modify the command or return a different execution
                        ...
                        
                }
                //the super call will be to the delegate instance
                return super.createExecution(command, executionContext, metadata, connection);
        }
        ...     
}

@Translator(name="custom-delegator")
public class MyTranslator extends BaseDelegatingExecutionFactory<Object, Object> {
        
        @Override
        public Execution createExecution(Command command,
                        ExecutionContext executionContext, RuntimeMetadata metadata,
                        Object connection) throws TranslatorException {
                if (command instanceof Select) {
                        //modify the command or return a different execution
                        ...
                        
                }
                //the super call will be to the delegate instance
                return super.createExecution(command, executionContext, metadata, connection);
        }
        ...     
}

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You will bundle and deploy your custom delegating translator like any other custom translator development. To use your delegating translator in a VDB, you define a translator override that wires in the delegate.

<translator type="custom-delegator" name="my-translator">

     <property value="delegateName" name="name of the delegate instance"/>

     <!-- any custom properties you may have on your custom translator -->

</translator>

<translator type="custom-delegator" name="my-translator">

     <property value="delegateName" name="name of the delegate instance"/>

     <!-- any custom properties you may have on your custom translator -->

</translator>

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From the previous example the translator type is custom-delegator. Now my-translator can be used as a translator-name on a source and will proxy all calls to whatever delegate instance you assign.

Note

The delegate instance can be any translator instance whether configured by its own translator entry or only the name of a standard translator type. Using a BaseDelegatingExecutionFactory by default means that standard override translator property settings on your instance will have no effect, since the underlying delegate is called instead.

You may also wish to use a different class hierarchy and instead make your custom translator only implement DelegatingExecutionFactory instead.

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9.3. Delegating Translator

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