Can't seem to succeed to save datatable to database, VB.net (2013)

Hi

I'm probably doing something very stupid, because the problem is terribly simple, But I fail when trying to save a nicely filled small datatable (40 rows !) back to an SQL Server database.

The table is holding currency exchange rates, and has only 4 fields: a date field (datetime), a "From Currency" (varchar) field, a "To Currency" (varchar) field, and a Rate (float) field. The PK consists of the first 3 fields.

The contents of the table are derived from another table, so what I do is:
1 Delete all rows in that table
2 Load the empty table in a datatable in my already existing dataset
3 Create/add all new rows derived from the other table
4 Update the datatable adapter to insert the newly created rows in the DB table

Step 4 is where I get the ominous "Concurrency violation" error, and I really can't see why, as the source table has a completely similar structure and a primary key.

Here is the code:
    Public Sub UpdateFXRates(frm As Form, sText As String)
        Dim sTemp As String
        Dim RateUSDCHF As Double
        Dim dateOfRate As Date
        Dim i As Integer

        On Error GoTo EH

        RateUSDCHF = <the current USD/CHF excahnge rate, value around 0.95>

        '  Delete all rows in DB table before creating the new rows
        Dim cmd As New SqlCommand
        ' connSQL is a public variable of the module in which this sub is located
        connSQL.Open()
        cmd = New SqlCommand("DELETE FROM [FX Rates]", connSQL)
        cmd.ExecuteNonQuery()
        cmd.Dispose()
        connSQL.Close()

        ' Load empty table in datatable and generate the rows
        sTemp = "SELECT * FROM [FX Rates]"
        adapterSQL.SelectCommand.CommandText = sTemp
        adapterSQL.SelectCommand.Connection = connSQL
        ' dsMCR is the dataset, also defined as Public
        adapterSQL.Fill(dsMCR, "FX Rates")
        For i = 0 To dsMCR.Tables("Rates Daily").Rows.Count - 1
            ' Add new row
            dsMCR.Tables("FX Rates").NewRow()
            dsMCR.Tables("FX Rates").Rows.Add()
            dsMCR.Tables("FX Rates").AcceptChanges()
            ' Fill the data in row
            dsMCR.Tables("FX Rates").Rows(i).Item("Date of Rate") = dsMCR.Tables("Rates Daily").Rows(i).Item("Date of Rate")
            dsMCR.Tables("FX Rates").Rows(i).Item("From Currency") = "USD"
            dsMCR.Tables("FX Rates").Rows(i).Item("To Currency") = dsMCR.Tables("Rates Daily").Rows(i).Item("From Currency")
            dsMCR.Tables("FX Rates").Rows(i).Item("Rate") = dsMCR.Tables("Rates Daily").Rows(i).Item("Rate") / RateUSDCHF
        Next
        ' Store generated rows in DB table
        Dim cmdBuilder As New SqlCommandBuilder(adapterSQL)
        adapterSQL.Update(dsMCR, "FX Rates")                    <-------------- THAT'S where the ERROR happens
        sText = i & " rates in FX Rates table loaded for " & Format(dateOfRate, "dd.mm.yyyy")

XH:
        On Error Resume Next
        Exit Sub

EH:
        Call HandleErrors(sAppName, "Error: " & Err.Description & " in UpdateFXRates", dsMCR, connSQL)
        Resume XH

    End Sub

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When I look at the data in the datatable before the adapter.Update, it looks OK (I just checked randomly a few rows), and, as the source table has just as many rows and the same PK on its first 3 fields, there should not be any problems with the data and therefore with the insert.

Is there an obvious flaw in my code (I'm pretty new to datasets) ? If not, how can I find out on which row there is a problem ?

Thanks for your help
Bernard
LVL 1
bthouinAsked:
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ktaczalaCommented:
It's bad practice to use your actual data as a primary key .  Add another field called dataID as integer have that auto increment and assign it as Primary Key. Then the DB will take care of that field.
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bthouinAuthor Commented:
@ktaczala
>>It's bad practice to use your actual data as a primary key <<
Maybe. But I'm accessing an existing DB with about 100 tables, and probably 80% use partial key defined in a similar way, so I have to deal with it the way it is.

And your post is not answering my 2 questions.
0
Jacques Bourgeois (James Burger)PresidentCommented:
When you add a new row, its RowState is marked as Added. When you call AcceptChanges, it is changed to Unchanged. Then, when you change the values in the row, it is marked as Modified.

When you run the Update, the DataAdapter sees the row as modified, and triggers an UPDATE command. The row does not already exist in the database, and you receive your error.

Remove AcceptChanges so that the row keeps its RowState property to Added, and I think it will work.
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bthouinAuthor Commented:
Merci Jacques ! That was exactly the kind of explanations I needed. Works like a charm.

Actually, I used the recommended method:
- define a new row as dtNewRow = dataset.Tables("<table name>").NewRow()
- fill the data in this dtNewRow
- add the row when all fields are set, using the dtNewRow
- update the adapter for the table

(so no more AcceptChanges anyway)

and in the cases where I rebuild the table, delete first all rows in the physical DB table.

Thanks a ton.
Bernard
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