Appending Additional Join Expressions

You can set the query manager to automatically append an expression to every query it performs on a class. For example, you can add an expression that filters the database for the valid instances of a given class.

Use this to do the following:

• Filter logically deleted objects

• Enable two independent classes to share a single table without inheritance

• Filter historical versions of objects

Using Java

Using Java, configure a descriptor with additional join expressions by creating an amendment method (see "Configuring Amendment Methods"), and then using the DescriptorQueryManager methods setAdditionalJoinExpression or setMultipleTableJoinExpression, as Example 99-6 shows.

Example 99-6 Registering a Query That Includes a Join Expression

In Example 99-6, the join expression filters invalid instances of employee from the query.

public static void addToDescriptor(Descriptor descriptor)
{
    ExpressionBuilder builder = new ExpressionBuilder();
    descriptor.getQueryManager().setAdditionalJoinExpression(
        (builder.getField("EMP.STATUS").notEqual("DELETED")).and(
             builder.getField("EMP.STATUS").notEqual("HISTORICAL"))
    );
}