ISOF (Entity SQL)
Determines whether the type of an expression is of the specified type or one of its subtypes.
expression IS [ NOT ] OF ( [ ONLY ] type )
Any valid query expression to determine the type of.
Negates the EDM.Boolean result of IS OF.
Specifies that IS OF returns
true only if
expression is of type
type and not any of one its subtypes.
The type to test
expression against. The type must be namespace-qualified.
expression is of type T and T is either a base type, or a derived type of
type; null if
expression is null at runtime; otherwise,
expression IS NOT OF (type) and
expression IS NOT OF (ONLY type) are syntactically equivalent to
NOT (expression IS OF (type)) and
NOT (expression IS OF (ONLY type)), respectively.
The following table shows the behavior of
IS OF operator over some typical- and corner patterns. All exceptions are thrown from the client side before the provider gets invoked:
|null IS OF (EntityType)||Throws|
|null IS OF (ComplexType)||Throws|
|null IS OF (RowType)||Throws|
|TREAT (null AS EntityType) IS OF (EntityType)||Returns DBNull|
|TREAT (null AS ComplexType) IS OF (ComplexType)||Throws|
|TREAT (null AS RowType) IS OF (RowType)||Throws|
|EntityType IS OF (EntityType)||Returns true/false|
|ComplexType IS OF (ComplexType)||Throws|
|RowType IS OF (RowType)||Throws|
The following Entity SQL query uses the IS OF operator to determine the type of a query expression, and then uses the TREAT operator to convert an object of the type Course to a collection of objects of the type OnsiteCourse. The query is based on the School Model.
SELECT VALUE TREAT (course as SchoolModel.OnsiteCourse) FROM SchoolEntities.Courses as course WHERE course IS OF( SchoolModel.OnsiteCourse)