TFDMemTable - how to clear structure?

[Jacek Laskowski 57]

How to clear structure of TFDMemTable? Not only data like in EmptyDataset() method, but fields, indexes, filters, etc. too.

Is possible?

[Lars Fosdal 1791]

Free/Create ?

[Kryvich 165]

mt.Free;
mt := TFDMemTable.Create(...);

 

[Jacek Laskowski 57]

This is not a very sophisticated solution 🙂

I was hoping for something better. But... thanks.

[Lars Fosdal 1791]

There are various ClearXxx methods for TFDMemTable, but it is not obvious which one(s) to call, or in which order, and if they actually reset the whole thing.
The above suggestions, on the other hand, are solid.

[Wloochacz 2]

Hello Jaca! :)

There is no simple solution for that.

However, I would suggest basing your own solution on the CopyDataSet code.
Note that if you specify the coStructure parameter in the options of CopyDataSet method, you will get what you want.
Almost ;-)

[teri 0]

Hello -

 

I'm having same/similar issue when I try to reuse a TFDMemTable to load varying column count csv files.

 

I read in the csv's header, construct the table fields then create the table. The second time it's run, I get a duplicate FieldDef error. 

 

fdmColumns is a TFDMemTable containing the list of column headings. fdmColumnValues is the TFDMemTable I want to load the contents of the csv file into. What am I missing?

 

Teri

 

  procedure DefineTable;
  begin
    fdmColumns.First;
    fdmColumnValues.Free;
    fdmColumnValues := TFDMemTable.Create(self);
    while not fdmColumns.eof do
    begin
      with fdmColumnValues.FieldDefs.AddFieldDef do
      begin
        Name := fdmColumns['ColumnName'];
        DataType := ftString;
      end;
      fdmColumns.Next;
    end;
    fdmColumnValues.CreateDataSet;
    dsColumnValues.DataSet := fdmColumnValues;
  end;

 

[Hans J. Ellingsgaard 21]

When you are defining all the fields in runtime, why not also create the table in runtime?

[Jeff Overcash 2]

Clear not only the Fields property but the FieldDefs too.  Do this while the dataset is closed.  Then you can rebuild your new fielddefs.

 

  if FDMemTable1.Active then
  begin
    FDMemTable1.Close;
    FDMemTable1.Fields.Clear;
    FDMemTable1.FieldDefs.Clear;
  end;

 

Now it is ready for you to define the new columns.  Index etc done the same way, just clear their definitions.  Don't forget there are both an Indexes and an IndexDef, both should be cleared.  Filter you would just assign the empty string.

[teri 0]

Thanks for the responses. I was actually clearing the dataset fdmColumnValues correctly, by clearing Fields and FieldDefs, but I had neglected to empty the fdmColumns dataset which I was using to define the field names. Thus, I was getting a duplicate field error. DOH!

 

Teri

 

[adyble 0]

Hi

I'm having exactly the same problem - I've simplified my process for the purpose of this post - 

 

QryChart.Sql.Text := 'SELECT CHARTSERIES, TOTAL, CHARTDATE FROM ORDERS' ;

QryChart.Open ;

 

memChartData.Close ;
memChartData.Indexes.Clear;
memChartData.IndexDefs.Clear;

memChartData.Fields.Clear;
memChartData.FieldDefs.Clear;

memChartData.CopyDataSet(dmData.QryChart, [coStructure, coRestart, coAppend]);

 

So far, no problem. Then

 

QryChart.Close ;

QryChart.Sql.Text := 'SELECT CHARTSERIES, TOTAL FROM ORDERS' ;

QryChart.Open ;

 

memChartData.Close ;
memChartData.Indexes.Clear;
memChartData.IndexDefs.Clear;

memChartData.Fields.Clear;
memChartData.FieldDefs.Clear;

memChartData.CopyDataSet(dmData.QryChart, [coStructure, coRestart, coAppend]);

 

It fails on CopyDataSet with the message CHARTDATE object not found, so it clearly hasn't removed that field form the defs.

 

Thanks for any advice.

Andy

 

[Kryvich 165]

See my comment from 2020.