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Inferring Relationships

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If an element that is inferred as a table has a child element that is also inferred as a table, a DataRelation will be created between the two tables. A new column with a name of "ParentTableName_Id" will be added to both the table created for the parent element, and the table created for the child element. The ColumnMapping property of this identity column will be set to MappingType.Hidden. The column will be an auto-incrementing primary key for the parent table, and will be used for the DataRelation between the two tables. The data type of the added identity column will be System.Int32, unlike the data type of all other inferred columns, which is System.String. A ForeignKeyConstraint with DeleteRule = Cascade will also be created using the new column in both the parent and child tables.

For example, consider the following XML:

<DocumentElement>
  <Element1>
    <ChildElement1 attr1="value1" attr2="value2"/>
    <ChildElement2>Text2</ChildElement2>
  </Element1>
</DocumentElement>

The inference process will produce two tables: "Element1" and "ChildElement1".

The "Element1" table will have two columns: "Element1_Id" and "ChildElement2". The ColumnMapping property of the "Element1_Id" column will be set to MappingType.Hidden. The ColumnMapping property of the "ChildElement2" column will be set to MappingType.Element. The "Element1_Id" column will be set as the primary key of the "Element1" table.

The "ChildElement1" table will have three columns: "attr1", "attr2" and "Element1_Id". The ColumnMapping property for the "attr1" and "attr2" columns will be set to MappingType.Attribute. The ColumnMapping property of the " Element1_Id" column will be set to MappingType.Hidden.

A DataRelation and ForeignKeyConstraint will be created using the "Element1_Id" columns from both tables.

DataSet: DocumentElement

Table: Element1

Element1_Id ChildElement2
0 Text2

Table: ChildElement1

attr1 attr2 Element1_Id
value1 value2 0

DataRelation: Element1_ChildElement1

ParentTable: Element1

ParentColumn: Element1_Id

ChildTable: ChildElement1

ChildColumn: Element1_Id

Nested: True

ForeignKeyConstraint: Element1_ChildElement1

Column: Element1_Id

ParentTable: Element1

ChildTable: ChildElement1

DeleteRule: Cascade

AcceptRejectRule: None

See Also

Inferring DataSet Relational Structure from XML | Loading a DataSet from XML | Loading DataSet Schema Information from XML | Nested DataRelations | XML and the DataSet | Creating and Using DataSets