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vb.net OleDbDataAdapter or SqlDataAdapter

Posted on 2006-07-11
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I want to put all the code to communicate with my db in a module.

In a form, if I need to fill a combo box with a table from my db, I currently doing something like this:
        Dim dataadapter As New SqlDataAdapter
        Dim dataAdapter As New OleDb.OleDbDataAdapter(strSelect, myConnection)
        Dim table As New DataTable()
        dataAdapter.Fill(table)
        cmbBox.DataSource = table
        cmbBox.DisplayMember = "description"
        cmbBox.ValueMember = "ID"

If I have a function return a dataadapter, it would help me put the sql stuff in my new module.
The reason I am doing this is because I don't know what kind of db I am going to be using.
How can I call a function if I don't know if I am going to use a OleDbDataAdapter or SqlDataAdapter.

like
        Dim dataAdapter As New OleDb.OleDbDataAdapter
        dataAdapter = mynewfunction(strSelect)

or
        Dim dataAdapter As New SqlDataAdapter
        dataAdapter = mynewfunction(strSelect)


I don't mind changing code in my db module, but don't want to have to change code every time I call a function from this module.

Is there any way to have a more generic dataadapter?

If there is another solution, please let me know.
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Question by:jackjohnson44
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Accepted Solution

by:
Carl Tawn earned 2000 total points
ID: 17083572
Yes. You can delcare an object using the interface implemented by each of the DataAdapters:

    Dim dataAdapter As IDataAdapter
   
Any if you are returning a DataAdapter from a method declare the return type as IDataAdapter.
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Author Comment

by:jackjohnson44
ID: 17083585
thanks, I am new to this, what does the "I" stand for?

Is this common in .net?
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LVL 52

Expert Comment

by:Carl Tawn
ID: 17083603
Its a prefix that indicates that it is an interface rather than a class. Its a common convention throughout most OO languages.
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Author Comment

by:jackjohnson44
ID: 17083690
I tried below, getDataAdapter returns IDataAdapter
It says "table" DataTable can't be converted to DataSet.
What am I doing wrong?

        Dim dataAdapter As IDataAdapter

        dataadapter = getDataAdapter("SELECT ID, description FROM Tests")

        Dim table As New DataTable()

        dataAdapter.Fill(table)

        cmbBox.DataSource = table
        cmbBox.DisplayMember = "description"
        cmbBox.ValueMember = "ID"
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LVL 52

Expert Comment

by:Carl Tawn
ID: 17083722
What does getDataAdapter do ? It sounds like its returning a DataTable rather than a DataAdapter. If thats the case the you can just return DataTable as that is a generic type across all the data providers.
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Author Comment

by:jackjohnson44
ID: 17083739
Thanks a lot for your help.

It should be returning a IDataAdapter

    Public Function getDataAdapter(ByVal selectString As String) As IDataAdapter
        Dim myData As New DataSet()
        Dim myConnection As New OleDb.OleDbConnection("mystring, this works")

        myConnection.Open()

        Dim dataAdapter As New OleDb.OleDbDataAdapter(selectString, myConnection)

        getDataAdapter = dataAdapter

    End Function

do I have to convert something?
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LVL 52

Expert Comment

by:Carl Tawn
ID: 17083786
Ah, didn't read the post properly. This line:

    dataAdapter.Fill(table)

Is expecting a DataSet rather than a DataTable:

    Dim ds As New DataSet()
    dataAdapter.Fill(ds)
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Author Comment

by:jackjohnson44
ID: 17083859
Thanks, but I am confused now.
I thought I was supposed to use a IDataAdapter

        Dim dataAdapter As IDataAdapter
        dataadapter = getDataAdapter("SELECT ID, description FROM Tests")
        Dim table As New DataTable()
        dataAdapter.Fill(table)
        cmbBox.DataSource = table
        cmbBox.DisplayMember = "description"
        cmbBox.ValueMember = "ID"
0
 
LVL 52

Expert Comment

by:Carl Tawn
ID: 17084109
dataAdapter and the return value from getDataAdapter() should be IDataAdapter. The Fill() method of that DataAdapter takes a DataSet as a parameter. It is that that the compiler was complaining about.
0
 

Author Comment

by:jackjohnson44
ID: 17084367
Then how do you fill a combo box with a dataset?

I was using a datatable before.

This works
        Dim table As New DataTable
        dataAdapter.Fill(table)
        cmbTestTesting.DataSource = table
        cmbTestTesting.DisplayMember = "description"
        cmbTestTesting.ValueMember = "ID"

This does not

        Dim table As New DataSet
        dataAdapter.Fill(table)
        cmbTestTesting.DataSource = table
        cmbTestTesting.DisplayMember = "description"
        cmbTestTesting.ValueMember = "ID"
0
 
LVL 52

Expert Comment

by:Carl Tawn
ID: 17084391
The DataSet is a collcetion of DataTables, so you would use:

        Dim table As New DataSet
        dataAdapter.Fill(table)
        cmbTestTesting.DataSource = table.Tables(0)
        cmbTestTesting.DisplayMember = "description"
        cmbTestTesting.ValueMember = "ID"
0
 

Author Comment

by:jackjohnson44
ID: 17084443
Thanks a lot
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