EclipseLink/Development/JPA 2.0/entity type expressions

Entity Type Expression

JPA 2.0 Root | bug 252009

Issue Summary

JPA 2.0 introduces JPQL expressions that allow a query to restrict results based on class types. This feature will require functionality to be added to EclipseLink.

See JPA 2.0 section 4.4.8 and 4.4.9 for details.

General Solution

Expression Support will be required that can provide a comparison with an extracted discriminator value.

Native Expression Support

through EclipseLink Enhancement 277509 1)ReportQuery will need return Class objects that the Type expression correlates to 2) Type expressions need to be supported that take parameters and constants representing Java Classes that will evaluate to String/Int values used in these class's inheritance policy fields 3) Type expresions also need to operate on expressions representing relationships and entities, allowing them all to be compared

Public API

*

public Expression getClassForInheritance()

returns a Type expression operating on the base expression. Examples:

expressionBuilder.get("project").getClassForInheritance().equals(LargeProject.class)

*

public Expression getClassForInheritance(Class clazz)

This returns a Type expresssion using the clazz argument to form a ConstantExpression as its base expression. Example:

expressionBuilder.getClassForInheritance().equals( (new ConstantExpression(LargeProject.class)).getClassForInheritance())

*

public static Expression getClassForInheritance(Expression expression)

This static method follows the form of other functions in Expression, allowing the expression argument passed in to be used as the base expression. Example:

builder.getTable("PROJECT").getField("TYPE").equals(Expression.getInheritanceType(builder.getParameter("parameter1")))

Open Issues

Method names for the public expression api.  The getClassForInheritance() used above was arbitrarily picked because getType() is difficult to interpret when reading expression code.  Other options might be getEntityType() or getClassType().
 

Work Required

1. Develop model for testing

   approx 1 day

2. Update Processing

   approx 6 days - creating expression support: EclipseLink Enhancement 277509

   approx 3 days - updating Parser