Connection string:
Books SELECT command:
Authors SELECT command:
Prices SELECT command:
Public Function BooksDataSet(strConnect As String, _
strWhere As String) _
As DataSet
outConnect.innerText = strConnect 'display connection string
'specify the SELECT statement to extract the BookList data
Dim strSelectBooks As String
strSelectBooks = "SELECT * FROM BookList WHERE " & strWhere
outSelectBooks.innerText = strSelectBooks 'and display it
'specify the SELECT statement to extract the BookAuthor data
Dim strSelectAuthors As String
strSelectAuthors = "SELECT * FROM BookAuthors WHERE " & strWhere
outSelectAuthors.innerText = strSelectAuthors 'and display it
'specify the SELECT statement to extract the BookPrices data
Dim strSelectPrices As String
strSelectPrices = "SELECT * FROM BookPrices WHERE " & strWhere
outSelectPrices.innerText = strSelectAuthors 'and display it
'declare a variable to hold a DataSet object
'note that we have to create it outside the Try..Catch block
'as this is a separate block and so is a different scope
Dim objDataSet As New DataSet()
Try
'create a new Connection object using the connection string
Dim objConnect As New OleDbConnection(strConnect)
'create a new Command object
Dim objCommand As New OleDbCommand()
'set the properties
objCommand.Connection = objConnect
objCommand.CommandType = CommandType.Text
objCommand.CommandText = strSelectBooks
'create a new DataAdapter object
Dim objDataAdapter As New OleDbDataAdapter()
'and assign the Command object to it
objDataAdapter.SelectCommand = objCommand
'get the data from the "BookList" table in the database and
'put it into a table named "Books" in the DataSet object
objDataAdapter.Fill(objDataSet, "Books")
'change the SELECT statement in the ADOCommand object
objCommand.CommandText = strSelectAuthors
'then get data from "BookAuthors" table into the DataSet
objDataAdapter.Fill(objDataSet, "Authors")
'and do the same again to get the "BookPrices" data
objCommand.CommandText = strSelectPrices
objDataAdapter.Fill(objDataSet, "Prices")
'declare a variable to hold a DataRelation object
Dim objRelation As DataRelation
'create a Relation object to link Books and Authors
objRelation = New DataRelation("BookAuthors", _
objDataSet.Tables("Books").Columns("ISBN"), _
objDataSet.Tables("Authors").Columns("ISBN"))
'and add it to the DataSet object's Relations collection
objDataSet.Relations.Add(objRelation)
'now do the same to link Books and Prices
objRelation = New DataRelation("BookPrices", _
objDataSet.Tables("Books").Columns("ISBN"), _
objDataSet.Tables("Prices").Columns("ISBN"))
objDataSet.Relations.Add(objRelation)
Catch objError As Exception
'display error details
outError.innerHTML = "* Error while accesing data." _
& objError.Message & "" & objError.Source
'return Nothing on error
BooksDataSet = Nothing
Exit Function ' and stop execution
End Try
'display a success message
outError.innerHTML = "DataSet created and loaded."
'return our new disconnected DataSet object
Return objDataSet
End Function
