public async Task <IActionResult> GetAllSentencesByUserId(int id) { var sentencesLearnt = await _sentenceService.GetUserSentencesAsync(id); var sentencesUnlearnt = await _sentenceService.GetUserSentencesAsync(id, true); var mergedSentences = sentencesLearnt .Union(sentencesUnlearnt) .ToList(); if (mergedSentences == null) { return(NotFound()); } return(Ok(mergedSentences)); }