if-statementdelphisyntaxsyntax-errordelphi-10.4-sydney

E2029 '(' expected but 'THEN' found

So I’m trying to write a function in Delphi 10.4 that takes a JSON file out of a SQL table and shows all the items within on a grid.

One of those is in a date format which causes the app to crash, so naturally I try figuring out which it is so I can format it correctly.

However, the method I used to try and find it keeps showing the above error:

procedure InjectJSONIntoTable(Query: TFDQuery;
                              MemTable: TFDMemTable; Edit: TEdit);
  var
    jsonString, dummyString: string;
    jsonArr: TJSONArray;
    jsonItem: TJSONObject;
    jsonValue: TJSONValue;
    i, j: Integer;
  begin
    // applies the SQL command
    Query.SQL.Text := Edit.Text;
    Query.Open;
    // transforms the SQL return back into JSON
    jsonString := Query.FieldByName('jdoc').AsString;
    jsonArr := TJSonObject.ParseJSONValue(jsonString) as TJSONArray;
    // preps the table to receive the data
    MemTable.Close;
    MemTable.CreateDataSet;
    MemTable.Open;
    MemTable.Insert;
    // appends the data to the table;
    for i := 0 to jsonArr.Count - 1 do begin
      jsonItem := jsonArr.Items[i] as TJSonObject;
      for j := 0 to MemTable.Fields.Count - 1 do begin
        MemTable.Edit;
        jsonValue := jsonItem.GetValue(MemTable.FieldDefs[j].Name);
        if jsonValue.ClassType = TDateTime then
          ShowMessage('tralala');
        MemTable.Fields[j].AsString :=
          jsonItem.GetValue(MemTable.FieldDefs[j].Name).Value;
      end;
    end;

    MemTable.Post;
    // shows data on the table
  end;

if jsonValue.ClassType = TDateTime then
  ShowMessage('tralala');
             ^ '(' expected but 'THEN' found

And perhaps I’m blind but I honestly can’t figure out where the error is coming from.

I’ve tried a bunch of stuff, switching the order of the elements around, but the error either persists of a bunch of new errors show up.

Solution

  • The TJSONValue.ClassType() method returns a TClass, which can only point to TObject-derived types. TDateTime is not a class derived from TObject, so you can't use ClassType = TDateTime (or ClassType is TDateTime, like @Dúthomhas suggested).

    JSON has no concept of date/time values, so there is no TJSON... class implemented for TDateTime. A date/time would just be a string to JSON.

    As @JPRitchey mentioned, you can use the TJSONValue.TryGetValue() method to convert the value of jsonValue into a TDateTime, checking if that conversion succeeds or fails. Just note that TryGetValue<TDateTime>() will succeed ONLY IF either:

    Otherwise, TryGetValue<TDateTime>() will return False.

    If that does not suit your needs, you will have to check the JSON value yourself manually, eg:

    var dtValue: TDateTime;

jsonValue := jsonItem.GetValue(MemTable.FieldDefs[j].Name);

// use whatever makes sense for your particular use-case...
if TryStrToDateTime(jsonValue.Value, dtValue) then
  ShowMessage('tralala');

MemTable.Fields[j].AsString := jsonValue.Value;