Select with condition from a datatable in VB.net - sql

Question

I want to select a certain field from a datatable in VB based on the value of another field in the same row.
In SQL, it would easily be done by writing this query:
select error_message from table_errors where error_case="condition"
How do I do this if I have my SQL table filled in a datatable in VB?
How do I select the item("error_message") in the datatable based on the item("error_Case") field?
Any help would be appreciated

Answer 1

You can use Linq-To-DataSet:
Dim matchingRows As IEnumerable(Of DataRow) =
From row In table
Where row.Field(Of String)("error_case") = "condition"
If you just want one column (of course that works also in one step):
Dim errorMessages As IEnumerable(Of String) =
From row In matchingRows
Select row.Field(Of String)("error_message")
For Each error In errorMessages
Console.WriteLine(error)
Next
If you expect it to be just a single row use First or Single(throws an exception if there is more than one row):
Dim error As String = errorMessages.First()
Since First throws an exception if the sequence is empty you can use FirstOrDefault:
Dim error As String = errorMessages.FirstOrDefault() ' is null/Nothing in case of an empty sequence
All in one line (note that both Linq and DataTable.Select needs to use loops):
Dim ErrMessage As String = errorTable.AsEnumerable().
Where(Function(r) r.Field(Of String)("Error_Case") = TextCase.Text).
Select(Function(r) r.Field(Of String)("Error_Message")).
FirstOrDefault()

Answer 2

here is a worker version of the rough code
Dim connString As String = "select error_message from table_errors where error_case='condition'"
Dim conn As SqlClient.SqlConnection = New SqlClient.SqlConnection(connString)
conn.Open()
Dim cmd As SqlClient.SqlCommand = New SqlClient.SqlCommand(connString, conn)
Dim dTable As DataTable = New DataTable()
Dim dAdapter As SqlClient.SqlDataAdapter = New SqlClient.SqlDataAdapter(cmd)
dAdapter.Fill(dTable)
conn.Close()
Dim text As String
Dim dReader As DataTableReader = dTable.CreateDataReader()
While dReader.Read()
text = dReader.GetValue(0)
End While
dReader.Close()