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2.1.11 ReferentialConstraint

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In Entity Data Model (EDM), a ReferentialConstraint element can exist between the key of one entity type and the primitive property or properties of an associated entity type. A referential constraint is a constraint on the keys contained in the association type. In CSDL 1.0, CSDL 1.1, and CSDL 1.2, the referential constraint can exist only between the key properties of associated entities.

The two entity types are in a Principal-to-Dependent relationship, which can also be thought of as a type of parent-child relationship. When entities are related by an Association that specifies a referential constraint between the keys of the two entities, the dependent (child) entity object cannot exist without a valid relationship to a principal (parent) entity object.

ReferentialConstraint MUST specify which end is the PrincipalRole and which end is the DependentRole for the referential constraint.

The following is an example of ReferentialConstraint.

   <Association Name="FK_Employee_Employee_ManagerID">
     <End Role="Employee" Type="Adventureworks.Store.Employee" Multiplicity="1" />
     <End Role="Manager" Type="Adventureworks.Store.Manager" Multiplicity="0..1" />
     <ReferentialConstraint>
       <Principal Role="Employee">
         <PropertyRef Name="EmployeeID" />
       </Principal>
       <Dependent Role="Manager">
         <PropertyRef Name="ManagerID" />
       </Dependent>
     </ReferentialConstraint>
   </Association>

The following rules apply to the ReferentialConstraint element:

  • ReferentialConstraint MUST define exactly one Principal end role element and exactly one Dependent end role element.

  • ReferentialConstraint can contain any number of AnnotationAttribute attributes. The full names of the AnnotationAttribute attributes cannot collide.

  • A ReferentialConstraint element can contain a maximum of one Documentation element.

  • ReferentialConstraint can contain any number of AnnotationElement elements.

  • Child elements of ReferentialConstraint are to appear in this sequence: Documentation, Principal, Dependent, AnnotationElement.

Graphic representation in table format of the rules that apply to the ReferentialConstraint element.

All child elements are to appear in the order indicated.