Inferring Relationships

 

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_IdChildElement2
0Text2

Table: ChildElement1

attr1attr2Element1_Id
value1value20

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

Inferring DataSet Relational Structure from XML
Loading a DataSet from XML
Loading DataSet Schema Information from XML
Nesting DataRelations
Using XML in a DataSet
DataSets, DataTables, and DataViews
ADO.NET Managed Providers and DataSet Developer Center

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