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What is DataRelation with example in ADO.NET

Answer» FIRST of all we have to understand what is DataRelation object in ado.net.when we have to set realtionship between two or more than two columns we use DataRelation class for that in ado.net. We we create an object of datarelation its enforce to do some constraints on the realtionship. That constraint can be Unique ,Foreiegn key.
A DataRelation object permits to establish a parent-child relationship between two or more tables inside a DataSet object. The easiest way to create a DataRelation between two tables in a DataSet is to setup a primary key - foreign key relationship between the columns of a table.
To Under stand it we take and example how to set realtion:-

Dim Conn As SqlConnection
Dim da As SqlDataAdapter
Dim ds As DataSet
Dim RowParent As DataRow
Dim RowChild As DataRow
'below connection object is define in web.config file
Conn = NEW _SqlConnection(ConfigurationSettings.Appsettings("StringInWeb.Config"))
da = New SqlDataAdapter("SELECT * FROM Employees", Conn)
ds = New DataSet()
Try
Conn.Open()
da.Fill( ds,"Employees")
da.SelectCommand = New SQLCOMMAND("SELECT * FROM Salary", Conn)
da.Fill(ds, "Salary")
Catch ex As SqlException
Response.Write(ex.ToString())
Finally
Conn.Dispose()
END Try

'Next, Let us create a Data Relationship
ds.Relations.Add("Employee_Salary", ds.Tables("Employees").Columns("EmployeeID"),ds.Tables("Salary").Columns("EmployeeID"))

'Display the Employee and Child Salary in the Form
'Say we have a Label in the form
For each RowParent in ds.Tables("Employees").Rows
lblRelation.Text &= RowParent("Emp_Name")
For each RowChild in RowParent.GetChildRows("Employee_Salary")
lblRelation.Text &= "
" & RowChild("Sal_Amount")
Next
Next


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