Lookup creation in run time Problem

[m227]

Hello.
I found it impossible to create lookup field in run time.

Code: Select all

  vtZamowienie.FieldByName('Sklep_ID').Visible    := True; // to check that this field is present

  vtZamowienie.Close;
  with TStringField.Create(vtZamowienie) do
  begin
      FieldKind := fkLookup;
      FieldName := 'Sklep';
      DataSet   := vtZamowienie;
      Name      := DataSet.Name + FieldName;
      LookupDataSet := vtSklep;
      LookupKeyFields := 'ID';
      LookupResultField := 'Nazwa';
      KeyFields := 'Sklep_ID';
      Lookup := True;
      vtZamowienie.Open; // <----------- here starts error
      vtZamowienie.FieldDefs.Add(FieldName, ftString, 90, False);
  end;

It produces error vtZamowienie: Field 'Sklep_ID' not found. However it is in data set. Can somebody tell me where the error is?

[AlexP]

Hello,

I could not reproduce the problem.
Please send a complete small sample to alexp*devart*com to demonstrate it.

Also provide the following information:
- the exact version of VirtualTable.
- the exact version of your IDE;

[AlexP]

Hello,

To resolve the problem, you should add fields to the vtOrder.Fields list like:

Code: Select all

var
  Client_ID, ID: TIntegerField;
  Product: TStringField;
begin
  vtOrder.Close;
  Client_ID:= TIntegerField.Create(nil);
  Client_ID.FieldName := 'Client_ID';
  Client_ID.DataSet:= vtOrder;

  ID:= TIntegerField.Create(nil);
  ID.FieldName := 'ID';
  ID.DataSet:= vtOrder;

  Product:= TStringField.Create(nil);
  Product.FieldName := 'Product';
  Product.DataSet:= vtOrder;

  with TStringField.Create(vtOrder) do
   .....

or add them with the help of the Fields Editor visual form.

[m227]

Hello Alex.

Unfortunatelly in my real application I load data from file (TVirtualTable.LoadFromFile) so I cannot create this dataset in run-time (as far as i know VirtualTable file storage stores structure too).

My algorithm is:

1. Load VT from file with foreign keys (i.e. Order.Client_ID)
2. Add Lookup to other loaded VT (Client.ID)

I cannot declare lookup in design time cause it will be removed after loading VT.

Michal

[AlexP]

Hello,

In the next version of VirtualTable we will change its behavior - when data is loaded into VirtualTable, fields which are already declared will not be removed.

Now you can add the needed fields after loading data:

1. Load VT from file with foreign keys (i.e. Order.Client_ID)
2. Add the Client_ID field (As I wrote earlier)
3. Add Lookup to the other loaded VT (Client.ID)

[m227]

Hello again Alex. I'm afraid I don't get it.

After point 1. as you mentioned I already have Order.Client_ID field, so how can I add this field again in point 2?

If about update: My problem is not to retain initial fields after loading data from VTD but to be able to add new after loading, so probably your future solution will not suit me.

[AlexP]

Hello,

Below is an example of loading data from files to TvirtualTable and adding the LookUp field in the runtime:

Code: Select all

var
  Client_ID: TIntegerField;
  vtClient, vtOrder :TVirtualTable;
begin
  vtClient:= TVirtualTable.Create(nil);
  VtOrder:= TVirtualTable.Create(nil);

  vtClient.LoadFromFile('Client.vtd');
  vtClient.Open;
  vtOrder.LoadFromFile('Order.vtd');
  vtOrder.Open;


  vtOrder.Close;
  Client_ID:= TIntegerField.Create(nil);
  Client_ID.FieldName := 'Client_ID';
  Client_ID.DataSet:= vtOrder;

  with TStringField.Create(vtOrder) do
  begin
    FieldKind          := fkLookup;
    FieldName          := 'Client';
    DataSet            := vtOrder;
    Name               := DataSet.Name + FieldName;
    LookupDataSet      := vtClient;
    LookupKeyFields    := 'ID';
    LookupResultField  := 'Name';
    KeyFields          := 'Client_ID';
    Lookup             := True;
    vtOrder.Open;
    vtOrder.FieldDefs.Add(FieldName, ftString, 90, False);
  end;

Please change this sample so the problem can be reproduced with it.