I do not know Visual Basic as much as I know C or C#.

I'm going to check if a select query have any results in returned 'testDataset` and have some results, so I wrote below syntax:

If ((testDataset Is Nothing) Or (testDataset.Tables Is Nothing) Or testDataset.Tables.Count = 0 _
    Or (testDataset.Tables.Item(0).Rows Is Nothing) Or (testDataset.Tables.Item(0).Rows.Count = 0) _
    Or (testDataset.Tables.Item(0).Rows(0) Is Nothing)) Then
    MessageBox.Show("Dataset has no results!", "Database Query Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
    Return False
End If

In C when an expression inside logical OR comes true next expression will not be processed. But it seems this is not the case in Visual Basic. So I want to know how can I check several expressions in visual basic and stop processing next ones if one came true.

So my question is mainly can be asked as two questions:

1. How can I check several condition's using OR without processing next ones?

2. How can I check if Dataset has results (at least one row) and an specific column is present in that (at least one) row?

CodePudding user response：

You can use the null conditional operator to short circuit all those checks in one line. The ? after the member in this chain will stop evaluating subsequent members and return null if the member is null.

Return testDataset?.Tables?.Item(0)?.Rows?.Any() ' true if any, false if none

CodePudding user response：

This is overkill on checking for Nothing. Presumably you have created a DataSet and filled it with a DataTable. The table may not have any rows returned but neither the DataSet nor the DataTable is Nothing.

If you are only using a single table, then dispense with the DataSet.

Private dt As New DataTable

Private Sub GetData()
    Using cn As New SqlConnection(ConLocal),
            cmd As New SqlCommand("Select Top 10 * From Coffees", cn)
        cn.Open()
        Using reader = cmd.ExecuteReader
            dt.Load(reader)
        End Using
    End Using
End Sub

Private Function CheckTable() As Boolean
    If dt.Rows.Count > 0 Then
        Return True
    End If
    MessageBox.Show("Dataset has no results!", "Database Query Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
    Return False
End Function

CodePudding user response：

This - probably - is not an exact answer, but general advice...

The shortest way to catch error while reading data from dataset is to get a code into Try...Catch..Finally block.

Dim bRetVal As Boolean = True
Try
   'your code to read data
Catch ex As Exception
    MessageBox.Show("Something went wrong..." & vbCrLf  & vbCrLf & ex.Message, "Error while reading data", MessageBoxButtons.OK, MessageBoxIcon.Error)
    bRetVal = False
Finally
  Return bRetVal