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Map Implicit Relations Between Nested Schema Elements

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An XML Schema definition language (XSD) schema can have complex types nested inside one another. In this case, the mapping process applies default mapping and creates the following in the DataSet:

  • One table for each of the complex types (parent and child).

  • If no unique constraint exists on the parent, one additional primary key column per table definition named TableName_Id where TableName is the name of the parent table.

  • A primary key constraint on the parent table identifying the additional column as the primary key (by setting the IsPrimaryKey property to True). The constraint is named Constraint# where # is 1, 2, 3, and so on. For example, the default name for the first constraint is Constraint1.

  • A foreign key constraint on the child table identifying the additional column as the foreign key referring to the primary key of the parent table. The constraint is named ParentTable_ChildTable where ParentTable is the name of the parent table and ChildTable is the name of the child table.

  • A data relation between the parent and child tables.

The following example shows a schema where OrderDetail is a child element of Order.

<xs:schema id="MyDataSet" xmlns=""
            xmlns:xs="http://www.w3.org/2001/XMLSchema"
            xmlns:msdata="urn:schemas-microsoft-com:xml-msdata">  
  
 <xs:element name="MyDataSet" msdata:IsDataSet="true">  
   <xs:complexType>  
     <xs:choice maxOccurs="unbounded">  
       <xs:element name="Order">  
         <xs:complexType>  
          <xs:sequence>  
            <xs:element name="OrderNumber" type="xs:string" />  
            <xs:element name="EmpNumber" type="xs:string" />  
            <xs:element name="OrderDetail">  
              <xs:complexType>  
                <xs:sequence>  
                  <xs:element name="OrderNo" type="xs:string" />  
                  <xs:element name="ItemNo" type="xs:string" />  
                </xs:sequence>  
              </xs:complexType>  
            </xs:element>  
          </xs:sequence>  
         </xs:complexType>  
       </xs:element>  
     </xs:choice>  
   </xs:complexType>  
  </xs:element>  
</xs:schema>

The XML Schema mapping process creates the following in the DataSet:

  • An Order and an OrderDetail table.

    Order(OrderNumber, EmpNumber, Order_Id)  
OrderDetail(OrderNo, ItemNo, Order_Id)

  • A unique constraint on the Order table. Note that the IsPrimaryKey property is set to True.

    ConstraintName: Constraint1  
Type: UniqueConstraint  
Table: Order  
Columns: Order_Id
IsPrimaryKey: True

  • A foreign key constraint on the OrderDetail table.

    ConstraintName: Order_OrderDetail  
Type: ForeignKeyConstraint  
Table: OrderDetail  
Columns: Order_Id
RelatedTable: Order  
RelatedColumns: Order_Id

  • A relationship between the Order and OrderDetail tables. The Nested property for this relationship is set to True because the Order and OrderDetail elements are nested in the schema.

    ParentTable: Order  
ParentColumns: Order_Id
ChildTable: OrderDetail  
ChildColumns: Order_Id
ParentKeyConstraint: Constraint1  
ChildKeyConstraint: Order_OrderDetail  
RelationName: Order_OrderDetail  
Nested: True

See also