How to iterate through the fields of a TTable

Problem/Question/Abstract:

How to iterate through the fields of a TTable

Answer:

There are a number of reasons why a program might need to query the structure of a table used in the application. One reason is a prelude to creating TField components at run-time that represent the fields in the table. The information gleaned from the structure of the table form the basis of the TField components to be created.

The example below demonstrates how to iterate through the fields available in a TTable or TQuery. The example extracts information about the available fields and displays the information in a TListBox, but the same methodology can be used to provide information necessary for the dynamic building of TField descendants. The example uses a TTable as the data set, but a TQuery can be used in the same manner as both TTable and TQuery components incorporate the FieldDefs property the same way.

procedure TForm1.Button1Click(Sender: TObject);
var
  i: Integer;
  F: TFieldDef;
  D: string;
begin
  Table1.Active := True;
  ListBox1.Items.Clear;
  with Table1 do
  begin
    for i := 0 to FieldDefs.Count - 1 do
    begin
      F := FieldDefs.Items[i];
      case F.DataType of
        ftUnknown: D := 'Unknown';
        ftString: D := 'String';
        ftSmallint: D := 'SmallInt';
        ftInteger: D := 'Integer';
        ftWord: D := 'Word';
        ftBoolean: D := 'Boolean';
        ftFloat: D := 'Float';
        ftCurrency: D := 'Currency';
        ftBCD: D := 'BCD';
        ftDate: D := 'Date';
        ftTime: D := 'Time';
        ftDateTime: D := 'DateTime';
        ftBytes: D := 'Bytes';
        ftVarBytes: D := '';
        ftBlob: D := 'BLOB';
        ftMemo: D := 'Memo';
        ftGraphic: D := 'Graphic';
      else
        D := '';
      end;
      ListBox1.Items.Add(F.Name + ', ' + D);
    end;
  end;
  Table1.Active := False;
end;