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Finding out if a column in a DataTable has a relationship to another DataTable, and if so, to which column in that DataTable

Posted on 2007-11-30
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When looping through the columns of a DataTable in a DataSet in VB 2005, how can I find out if a column is linked (i.e. has a relatioship) to another DataTable in that DataSet, and if it is linked, to which column and DataTable?

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Question by:SETP
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VBRocks earned 2000 total points
ID: 20382911
It's very easy, you can just loop through the Relations collection of the DataSet.  

Here's an example:

        'Create 2 tables, add them to a DataSet and create a relationship between both:
        Dim tableA As New DataTable()
        tableA.Columns.Add("tableA_ID")
        tableA.Columns("tableA_ID").DataType = GetType(Int16)
        tableA.Columns.Add("Item")

        Dim tableB As New DataTable()
        tableB.Columns.Add("tableB_ID")
        tableB.Columns("tableB_ID").DataType = GetType(Int16)
        tableB.Columns.Add("tableA_ID")
        tableB.Columns("tableA_ID").DataType = GetType(Int16)
        tableB.Columns.Add("Item")


        'Create a DataSet and add both tables
        Dim ds As New DataSet()
        ds.Tables.Add(tableA)
        ds.Tables.Add(tableB)


        'Create a relationship between both tables:
        ds.Relations.Add("tableA_tableB", _
            New DataColumn() {tableA.Columns("tableA_ID")}, _
            New DataColumn() {tableB.Columns("tableA_ID")}, _
           False)



        'Now to find out what types of relationships exist in the DataSet,
        '    between which tables, and what columns are referenced:
        For Each rel As DataRelation In ds.Relations
            Debug.WriteLine("Parent table:  " & rel.ParentTable.TableName)

            For Each col As DataColumn In rel.ParentColumns
                Debug.WriteLine(vbTab & "Parent column:  " & col.ColumnName)
            Next

            Debug.WriteLine("Child table:  " & rel.ChildTable.TableName)

            For Each col As DataColumn In rel.ChildColumns
                Debug.WriteLine(vbTab & "Child column:  " & col.ColumnName)
            Next
        Next

        Stop

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Author Closing Comment

by:SETP
ID: 31411925
Thanks VBRocks!
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