Verifying if data exists in my Table using TClientDataSet in Delphi

Question

I am trying to verify if [specific] data exists in my table using TClientDataSet. I

Is there a way that I can do this in TClientDataSet?

I am avoiding to use query for some reason here.

Answer 1

The following shows how to check whether a TClientDataSet contains any data and how to find whether it contains a record with a field having a specific value (or a record containg a combination of values in multiple fields)

procedure TForm1.FormCreate(Sender: TObject);
var
  i : Integer;
  Field : TField;
  S : String;
begin

  //  Create 2 fields in the CDS

  Field := TIntegerField.Create(Self);
  Field.FieldName := 'ID';
  Field.FieldKind := fkData;
  Field.DataSet := CDS1;

  Field := TStringField.Create(Self);
  Field.FieldName := 'Name';
  Field.Size := 40;
  Field.FieldKind := fkData;
  Field.DataSet := CDS1;

  //  Next, set up the CDS; it will be empty initially
  CDS1.CreateDataSet;

  if CDS1.IsEmpty then
    ShowMessage('Is empty - no data')
  else
    ShowMessage('Something went wrong');

  CDS1.IndexFieldNames := 'Name;ID';
  CDS1.InsertRecord([1, 'One']);
  CDS1.InsertRecord([2, 'Two']);
  CDS1.InsertRecord([3, 'Three']);

  ShowMessage('DataSet now contains ' + IntToStr(CDS1.RecordCount) + ' records');

  S := 'Two';
  if CDS1.Locate('Name', S, []) then
    ShowMessage('Found record with Name = ' + S)
  else
    ShowMessage('Failed to find record with Name = ' + S);

  //  Following shows how to use Locate on more than one field
  //  Note: to use VarArrayOf, you need Variants in your uses list
  if CDS1.Locate('ID;Name', VarArrayOf([1, 'one']), [loCaseInsensitive])  then
    ShowMessage('Found record by multiple criteria');
end;

Note that setting the IndexFieldNames to 'Name;ID' is to speed up the Locate operation if there are a lot of records.