Delphi + SQLite + DB express select with parameters error

Question

I use Delphi XE3 and use SQLite database with DB express.

this is my user validation code:

function validateUser(UserName, Password: string): Boolean;
var
  AParams: TParams;
  SQLTxt: string;
  MD5 : TIdHashMessageDigest5;
  RecCount: integer; 
begin
  AParams := TParams.Create(nil);
  MD5 := TIdHashMessageDigest5.Create;
  try
    Result := False;
    AParams.CreateParam(ftString, 'username', ptInput).Value := UserName;
    AParams.CreateParam(ftString, 'password', ptInput).Value :=
      MD5.HashBytesAsHex(MD5.HashString(Password));
    SQLTxt := 'SELECT login_id FROM login WHERE '+
    'login_username = :username AND login_password = :password ;';
    with Form1.sqlqry1 do
    begin
      SQL.Clear;
      SQL.Text :=  SQLTxt;
      Params := AParams;
      //Params.Items[0].Value := AParams.Items[0].Value;
      //Params.Items[1].Value := AParams.Items[1].Value;
      Prepared := true;
      Open;
    end;
    RecCount := Form1.sqlqry1.RecordCount;// I have error here
    if RecCount = 0 then
      Result := False
    else
      Result := True;
    // end
  finally
    AParams.Free;
    MD5.Free;
  end;
end;

Application show me [0x0005]: Operation Not Supported error.

What is the problem? why?

Answer 1

You also don't need to use RecordCount (which is where you indicate the error is occurring). Use TDataSet.IsEmpty instead.

Also, from the documentation (emphasis mine):

Params is a collection of TParam objects that represent the parameters of a query or stored procedure specified by the SQL dataset. When you specify a query by setting the CommandText property (or the SQL property in TSQLQuery), the SQL dataset automatically parse the query and fills Params with a TParam object for every parameter in the query.

You don't need to manually create the Params; the dataset will do that for you automatically when you assign the SQL.

function validateUser(UserName, Password: string): Boolean;
var
  SQLTxt: string;
  MD5 : TIdHashMessageDigest5;
  RecCount: integer; 
begin
  MD5 := TIdHashMessageDigest5.Create;
  try
    Result := False;
    SQLTxt := 'SELECT login_id FROM login WHERE '+
    'login_username = :username AND login_password = :password ;';
    with Form1 do
    begin
      // Clear not needed when setting SQL.Text directly.
      sqlqry1.SQL.Text :=  SQLTxt; 
      sqlqry1.Params.ParamByName('username').AsString := UserName;
      sqlqry1.Params.ParamByName('password').AsString :=
               MD5.HashBytesAsHex(MD5.HashString(Password));

      sqlqry1.Open;
      Result := not sqlqry1.IsEmpty;
    end;
  finally
    MD5.Free;
  end;
end;