Creating Relationships in Access

Question

I got two tables in my access file. and I would like to create relationship between them. The following diagram is the relationship I created manually in Access.

However, I want to create the relationships in VB.net and here is my code:

    conn.Open()

    daBooks = New OleDb.OleDbDataAdapter("SELECT * FROM Books", conn)
    daAuthor = New OleDb.OleDbDataAdapter("SELECT * FROM  authors", conn)

    daBooks.Fill(ds, "Books")
    daAuthor.Fill(ds, "authors")

    conn.Close()

    'Set the relation
    Dim parentColumn As DataColumn
    parentColumn = ds.Tables("authors").Columns("AuthorID")

    Dim childColumn As DataColumn = New DataColumn
    Try
        childColumn = ds.Tables("Books").Columns("AuthorID")
    Catch ex As Exception
        MsgBox(ex.Message)
        Exit Sub
    End Try

    Dim a As String
    a = ds.Tables("authors").Rows(0).Item("AuthorID")
    Dim b As String
    b = ds.Tables("Books").Rows(0).Item("AuthorID")

    Dim relation As DataRelation = New  _
           System.Data.DataRelation("Books_Authors", parentColumn, childColumn)
    ds.Relations.Add(relation)

    RelationName.Text = relation.RelationName
    'End of setting relation

    Dim cb1 As New OleDb.OleDbCommandBuilder(daBooks)
    Dim cb2 As New OleDb.OleDbCommandBuilder(daAuthor)

    Try
        daBooks.Update(ds, "books")
    Catch ex As Exception
        MsgBox(ex.Message)
    End Try

    daAuthor.Update(ds, "authors")

However after I ran the code, it couldn't change the database. Can anyone help me with this so that I can create a new relationship for two tables in VB.NET.

Generally I think the problem is that the System.Data.DataRelation and ds.Relations.Add(relation) just create the relationship for the dataset but it hasn't been updated to the database through dataadapter or something else. Am I correct by saying so or it's because of other reasons. If I'm correct, then how to update the dataset to database?

Answer 1

You can create that relationship by executing an ALTER TABLE statement from your OleDb connection.

ALTER TABLE Books
ADD CONSTRAINT BooksRelationship
FOREIGN KEY (AuthorID) REFERENCES Authors (AuthorID);

Answer 2

You can create a macro in Access that creates a relationship between your tables and run it via VB.NET.
Here is a function to create a relation in MS Access:

Public Function MacroCreateRelation()

Dim db As DAO.Database

CreateRelation("Author", "IdAuthor", _
                           "Book", "IdAuthor")

Set db = Nothing  
End Function


Private Function CreateRelation(primaryTblName As String, _
    primaryFieldName As String, _
    foreignTblName As String, _
    foreignFieldName As String) As Boolean
On Error GoTo ErrHandler

Dim myDB As DAO.Database
Dim newRelation As DAO.Relation
Dim relatingField As DAO.Field
Dim relationName As String

relationName = primaryTblName + "_" + primaryFieldName + _
    "__" + foreignTblName + "_" + foreignFieldName

    Set myDB = CurrentmyDB()

    ' First create the relation
    Set newRelation = myDB.CreateRelation(relationName, _
        primaryTblName, foreignTblName)
    'field of the primary table
    Set relatingField = newRelation.CreateField(primaryFieldName)
    'Then the field of the the second table
    relatingField.ForeignName = foreignFieldName

    'now just add the field to the relation
    newRelation.Fields.Append relatingField

    'Last but not least add the relation to the db
    myDB.Relations.Append newRelation

    Set myDB = Nothing

    return True

Exit Function

    ErrHandler:
    Debug.Print Err.Description + " [ " + relationName + "]"
    return False

End Function

Then you have just to call the macro from VB.NET.