How to use MySqlHelper.UpdateDataSet - mysql

Question

I've searched around the web looking for samples on how to use MySqlHelper.UpdateDataSet but all I've found is:
Public Shared Sub UpdateDataSet( _
ByVal connectionString As String, _
ByVal commandText As String, _
ByVal ds As DataSet, _
ByVal tablename As String _
)
I'll be grateful if someone will give me:
an example of commandText because I didn't understand what kind of command I need to give;
an explanation of tablename because I need to know if is the name of a table of the DB or of the DataSet or both (with the same name);
a vb.net code example (to start testing).
I tryed to use the command this way:
Private Sub Btn_Mod_Dataset_Click(sender As Object, e As EventArgs) Handles Btn_Mod_Dataset.Click
Dim SqlStr$ = "SELECT * FROM MyTest.Users"
Using DS_Test As DataSet = DB_Functions.mQuery(SqlStr)
With DS_Test
.Tables(0).TableName = "Users"
Dim User$ = .Tables(0).Rows(0)("UserName").ToString
MsgBox(User)
.Tables(0).Rows(0)("User") = "Upd_Test"
User = .Tables(0).Rows(0)("UserName").ToString
MsgBox(User)
End With
Dim DB_Name = "MyTest"
Dim connectionString$ = "datasource=localhost;username=" + UserDB _
+ ";password=" + Password + ";database=" + DB_Name
MySqlHelper.UpdateDataSet(connectionString, _
"Update MyTest.Users Set UserName = 'Test_Ok' WHERE UserName = 'Steve'", _
DS_Test, "Users")
End Using
End Sub
This gives me
System.NullReferenceException' in System.Data.dll
EDIT (to explain my code):
a) DB_Functions is a sepate class where I've stored some function to use on a MySql DataBase. mQuery is a function who extract query result into a dataset;
b) 'User' is a field Name : I've changed it to 'UserName' but same result;
d) The code between With and End With is just a test to see what happens;
NOTE that the code gives error but my DB is updated as in the commandText String. I don't understand what happens

Answer 1

This might get you part of the way.
First get rid of DB_Functions. MySQLHelper has a method to create the DataSet for you; in general, db Ops are so query-specific that there is very little that is generic and reusable. The exception to this is building the ConnectionString: MySQL has gobs of cool options you can enable/disable via the connection string. But for that you just need the standard MySqlConnectionStringBuilder.
Build a DataSet:
' form/class level vars
Private dsSample As DataSet
Private MySqlConnStr As String = "..."
...
Dim SQL = "SELECT Id, FirstName, Middle, LastName FROM Employee"
Using dbcon As New MySqlConnection(MySQLConnStr)
dsSample = MySqlHelper.ExecuteDataset(dbcon, SQL)
dsSample.Tables(0).TableName = "Emps"
End Using
There does not appear to be a way to specify a tablename when you build it, so that is a separate step.
Update a Record
To update a single row, you want ExecuteNonQuery; this will also allow you to use Parameters:
Dim uSQL = "UPDATE Employee SET Middle = #p1 WHERE Id = #p2"
Using dbcon As New MySqlConnection(MySQLConnStr)
Dim params(1) As MySqlParameter
params(0) = New MySqlParameter("#p1", MySqlDbType.String)
params(0).Value = "Q"
params(1) = New MySqlParameter("#p2", MySqlDbType.Int32)
params(1).Value = 4583
dbcon.Open()
Dim rows = MySqlHelper.ExecuteNonQuery(dbcon, uSQL, params)
End Using
Again, this is not really any simpler than using a fully configured DataAdapter, which would be simply:
dsSample.Tables("Emps").Rows(1).Item("Middle") = "X"
daSample.Update(dsSample.Tables("Emps"))
I am not exactly sure what value the UpdateDataSet method adds. I think it is the "helper" counterpart for the above, but since it doesn't provide for Parameters, I don't have much use for it. The docs for it are sketchy.
The commandtext would appear to be the SQL for a single row. Note that the DataAdapter.Update method above would add any new rows added, delete the deleted ones and update values for any row with changed values - potentially dozens or even hundreds of db Ops with one line of code.

Answer 2

My funtion gets string query and returns datatable. So u can set dataset.tables .
Public Function mysql(ByVal str_query As String) As DataTable
Dim adptr As New MySqlDataAdapter
Dim filltab As New DataTable
Try
Using cnn As New MySqlConnection("server=" & mysql_server & _
";user=" & mysql_user & ";password=" & mysql_password & _
";database=" & mysql_database & ";Allow User Variables=True")
Using cmd As New MySqlCommand(str_query, cnn)
cnn.Open()
adptr = New MySqlDataAdapter(cmd)
adptr.Fill(filltab)
cnn.Close()
End Using
End Using
Catch ex As Exception
'you can log mysql errors into a file here log(ex.ToString)
End Try
Return filltab
End Function