A Brief Overview of Relational Data Access

DataRelation Object Reference

The reference information for the DataRelation object isn't terribly interesting, to be honest. The object exposes no methods and no events—only properties. However, to leave these out would somehow feel like cheating.

Properties of the DataRelation Object

Most of the DataRelation object's properties are read-only. You can set their value only using the DataRelation object's constructors. The commonly used properties are described in Table 7-1.

Table 7-1 Commonly Used Properties of the DataRelation Object

Property

Data Type

Description

ChildColumns

Array of DataColumn objects

Indicates the child columns that define the relation. This property is read-only.

ChildKeyConstraint

ForeignKeyConstraint

Indicates the foreign key constraint in the child table in the relation. This property is read-only.

ChildTable

DataTable

Indicates the child table in the relation. This property is read-only.

DataSet

DataSet

Indicates the DataSet in which the DataRelation resides. This property is read-only.

ExtendedProperties

PropertyCollection

Indicates a collection of dynamic properties.

Nested

Boolean

Indicates whether the child rows are child elements when the DataSet is stored as XML.

ParentColumns

Array of DataColumn objects

Indicates the parent columns that define the relation. This property is read-only.

ParentKeyConstraint

UniqueConstraint

Indicates the unique constraint in the parent table in the relation. This property is read-only.

ParentTable

DataTable

Indicates the parent table in the relation. This property is read-only.

RelationName

String

Indicates the name of the relation.

ChildColumns Property

The ChildColumns property returns an array that contains the DataColumn object or objects from the child DataTable in the DataRelation. This property is read-only.

ChildKeyConstraint Property

The ChildKeyConstraint property returns the ForeignKeyConstraint referenced by the DataRelation. If you created a DataRelation that does not use constraints, this property returns Nothing or null, depending on your language of choice. The ChildKeyConstraint property is read-only.

ChildTable Property

The ChildTable property returns the child DataTable in the DataRelation. This property is read-only.

DataSet Property

The DataSet property returns the DataSet in which the DataRelation resides. This property is read-only.

ExtendedProperties Property

Like the DataSet, DataTable, and DataColumn objects, the DataRelation object also exposes an ExtendedProperties property in which you can store additional information.

Nested Property

The Nested property controls the location of the contents of the child DataTable when the DataSet is stored in XML format using the DataSet object's WriteXml method. This is one of the few read-write properties of the DataRelation object.

If the Nested property is set to False, which is the default, the data in the child DataTable will be separate from the data in the parent DataTable. As you can see here, without looking at the schema information for the DataSet, you wouldn't know that there is a DataRelation between the DataTable objects:

Not Nested

<Customers>     <CustomerID>ALFKI</CustomerID>     <CompanyName>Alfreds Futterkiste</CompanyName> </Customers> <Customers>     <CustomerID>ANATR</CustomerID>     <CompanyName>Ana Trujillo Emparedados y helados</CompanyName> </Customers> ... <Orders>     <OrderID>10308</OrderID>     <CustomerID>ANATR</CustomerID> </Orders> <Orders>     <OrderID>10355</OrderID>     <CustomerID>AROUT</CustomerID> </Orders> ...

Setting the Nested property to True causes ADO.NET to embed the data in the child DataTable within the data for the parent DataTable, as shown here:

Nested

<Customers>     <CustomerID>ALFKI</CustomerID>     <CompanyName>Alfreds Futterkiste</CompanyName>     <Orders>         <OrderID>10643</OrderID>         <CustomerID>ALFKI</CustomerID>     </Orders>     <Orders>         <OrderID>10692</OrderID>         <CustomerID>ALFKI</CustomerID>     </Orders>     ... </Customers> <Customers>     <CustomerID>ANATR</CustomerID>     <CompanyName>Ana Trujillo Emparedados y helados</CompanyName>     <Orders>         <OrderID>10308</OrderID>         <CustomerID>ANATR</CustomerID>     </Orders>     <Orders>         <OrderID>10625</OrderID>         <CustomerID>ANATR</CustomerID>     </Orders>     ... </Customers> ...

ParentColumns Property

The ParentColumns property returns an array that contains the DataColumn objects from the parent DataTable in the DataRelation. This property is read-only.

ParentKeyConstraint Property

The ParentKeyConstraint property returns the UniqueConstraint referenced by the DataRelation. If you created a DataRelation that does not use constraints, this property returns Nothing or null, depending on your language of choice. The ParentKeyConstraint property is read-only.

ParentTable Property

The ParentTable property returns the parent DataTable in the DataRelation. This property is read-only.

RelationName Property

The RelationName property is read-write and can be used to set or retrieve the name of the DataRelation.



Microsoft ADO. NET Core Reference
Microsoft ADO.NET (Core Reference) (PRO-Developer)
ISBN: 0735614237
EAN: 2147483647
Year: 2002
Pages: 104
Authors: David Sceppa

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