当你在数据表上循环时如何删除行

Question

For Each Dr As DataRow In InvoiceDT.Rows
    Dim DrResult As Array = PaymentInvoiceDT.Select("Amount='" & Dr("Amount").ToString() & "'")
    If DrResult.Length > 0 Then
        ''some code
    Else
        InvoiceDT.Rows.remove(Dr) 
    End If
Next

It is giving error because when you changed something in datatable, its index get changed.

Answer 1

You won't be able to do this in a For Each loop because when you remove something, the collection has changed and you can't enumerate it anymore.

What you need is a reversed For loop.

For i as Integer = Invoice.Rows.Count -1 to 0 Step -1
    Dim DrResult As Array = PaymentInvoiceDT.Select("Amount='" & Invoice.Rows(i).("Amount").ToString() & "'")
    If DrResult.Length > 0 Then
        'some code
    Else
        InvoiceDT.Rows.remove(InvoiceDT.Rows(i)) 
    End If
Next

This will still work even as you remove rows because the ones you're not touching aren't having their indexes changed and it doesn't use an enumeration.

Answer 2

Sai, it fails because you should not really delete the rows while looping in all table rows.

an example of what you could do, in C# is this one:

   DataTable dt = CreateDataSource();

    DataRow[] rows = (from t in dt.AsEnumerable().Cast<DataRow>()
                      where t.Field<int>("ID") == 1
                      select t).ToArray();

    foreach (DataRow row in rows)
    {
        dt.Rows.Remove(row);
    }

so as you see you first select all rows to delete with LINQ then you loop only on the resulting rows and remove them from the source table.

sorry no time to write this in VB.NET but the idea should be clear I hope.

Answer 3

My problem was that I needed to loop a table multiple times, so after deleting rows in the first round it would throw an exception when coming to the index of a previously deleted row. I ended up cloning the table and copying into it the rows I wanted to keep.

Dim NewInvoiceDT as DataTable = InvoiceDT.clone
For Each Dr As DataRow In InvoiceDT.Rows
    If 'some statement
        Dim NewDr as DataRow = NewInvoiceDT.Rows.Add
        NewDr.ItemArray = Dr.ItemArray
    End if  
Next

Answer 4

To iterate through a DataTable and remove rows conditionally (eg: row having column_id as 16), you can use the following code:

Dim iterateIndex As Integer = 0    
Dim newDataTable As DataTable = originalDataTable.Copy
For Each row As DataRow In newDataTable.Rows
   If row("column_id") = 16 Then
      originalDataTable.Rows.RemoveAt(iterateIndex)
   Else
      iterateIndex += 1
   End If
Next

Answer 5

It's simple

For i = 0 To dt.Rows.Count - 1
'DO ....  then delete....
dt.Rows(0).Delete()
Next

Answer 6

您不能使用简单的DELETE语句进行DELETE吗？

DELETE FROM xxx WHERE Amount = yyy