Comparing datatables / identify identical datatables - mysql

Question

I am working with VB.net and mysql, I have a function which fills a datatable with mysql content then posts it (as appropriate) to a listview. This function is currently on a timer which activates every 5 seconds which unfortunately does horrible destruction to the drag-and-drop features of my software.
The solution: I have decided after filling the content to the listview to copy the content from the active datatable to another datatable for comparison, every time the data is taken from the mysql db have it save to a datatable and compare the two datatables - if they are not identical the software should run the function however if they are identical there is no reason to update the listview with the same exact data.
Public pendrun As New DataTable
Public postrun As New DataTable
Private Sub Timer1_Tick(sender As Object, e As EventArgs) Handles Timer1.Tick
con.ConnectionString = "server=localhost;" _
& "user id=user;" _
& "password=password;" _
& "database=DMT"
adptr = New MySqlDataAdapter("Select * from data", con)
Try
adptr.Fill(pendrun)
Catch err As Exception
Dim strError As String = "Exception: & err.ToString()"
End Try
if pendrun <> postrun then
ListView2.Items.Clear()
pendrun.Clear()
' commands to add
' pendrun datatable information
' to listview
postrun = pendrun 'to transfer data to the holding datatable
end if
the problem is
if pendrun <> postrun then
is not a valid way to compare datatables.
How do I identify if the datatables are identical (all rows and columns identical)

Answer 1

There's no built-in understanding of "identical" for types you've defined. You'll need to write that logic.
Essentially you need to build a function which accepts two DataTables as input, compares them in accordance with whatever business logic you define, and returns a Boolean indicating whether or not they pass that logic. Something like this:
Function TablesAreEqual(ByVal firstTable As DataTable, ByVal secondTable As DataTable) As Boolean
' Compare your tables, probably by looping through rows/values
Return areEqual
End Function
Then you'd use that function in your comparison:
If TablesAreEqual(pendrun, postrun) Then

Answer 2

Here is the resulting code I created to deal with this problem - thanks to David for the direction
Function TablesAreEqual(ByVal firstTable As DataTable, ByVal secondTable As DataTable) As Boolean
dim db1 As String = ""
dim db2 As String = ""
For rown As Integer = 0 To firstTable.Rows.Count - 1
For cown As Integer = 0 To firstTable.Columns.Count - 1
db1 = db1 & firstTable.Rows(rown).Item(cown)
Next
Next
For rown As Integer = 0 To secondTable.Rows.Count - 1
For cown As Integer = 0 To secondTable.Columns.Count - 1
db2 = db2 & secondTable.Rows(rown).Item(cown)
Next
Next
Return db1 = db2
End Function

Answer 3

If you want to use your pendrun and postrun datatables
try to serialize "writeXml" datatables and compare them.
Anyway i suggest you to think about a different approach instead of using a polling timer.

Answer 4

Better yet why not put in logic to not get new data if it has not changed.
Don't know about MySQL but MSSQL has Notification and TimeStamp
The columns should only change with a schema change.
First compare count and if not the same for sure there was a change.
If counts are the same then loop through the columns and compare.
As soon as one does not compare then done immediately return false.
On rows same thing. First test row count.
After that need to compare row by row and column by column.
Remember to sort the select statement so you would catch rows out of order.
And again as soon as one does not compare stop and return false.
Right with less code than you have in your answer
My inserts are C#
Function TablesAreEqual(ByVal firstTable As DataTable, ByVal secondTable As DataTable) As Boolean
if(firstTable.Rows.Count != secondTable.Rows.Count) return false;
if(firstTable.Columns.Count != secondTable.Columns.Count) return false;
For rown As Integer = 0 To firstTable.Rows.Count - 1
For cown As Integer = 0 To firstTable.Columns.Count - 1
if (firstTable.Rows(rown).Item(cown) != secondTable.Rows(rown).Item(cown)) return false;
Next
Next
return true;
End Function