title: How avoid duplicate records when use annotate() in queryset
body: <p>I get this queryset for some method an receive one record</p>
  <pre><code>candidates_qs = self.filter_job_type_language_zones(job_type_id, filter_languages, filter_zones)
  </code></pre>
  <p>Then i need to cast a charfield to integerfield to compare against some value</p>
  <pre><code>candidates_qs = self.filter_job_type_language_zones(job_type_id, filter_languages, filter_zones)
          candidates_qs = candidates_qs.annotate(
              # cast answer_text as integer to compare with question value
              as_integer=Cast('candidatejobtype__questions_answers__answer_text', IntegerField()))
  </code></pre>
  <p>After that my queryset have duplicated records. I try distinct() but didn't work. How avoid duplicate records?</p>