title: How can I get "ManyToManyField" values in the search filters of Haystack?
body: <p>I'm implementing a filtering functionality using haystack with elasticsearch. Now, I'm getting most of all the fields to filter however I can't get the <code>ManyToManyField</code> values. In the browser is appearing like the physical address not the readable value:</p>
  
  <p></p>
  
  <p>I've got in my model the code below:</p>
  
  <pre><code>class StudyLevel(models.Model):
      name_level = models.CharField(max_length=100, unique=True)
  
  class Institution(models.Model):
  .
  .
  level_study = models.ManyToManyField(StudyLevel, null=True)
  .
  .
  </code></pre>
  
  <p>In the search_indexes is the following:</p>
  
  <pre><code>class InstitutionIndex(indexes.SearchIndex, indexes.Indexable):
      .
      .
      level_study = indexes.CharField(model_attr='level_study', faceted=True)
  </code></pre>
  
  <p>Now, in the search html template is the problem:</p>
  
  <pre><code>                {% if facets.fields.level_study %}
                      &lt;div&gt;
                      &lt;h4&gt;Study Level&lt;/h4&gt;
                      &lt;ul&gt;
                      {% for level_study in facets.fields.level_study.all %}
                          &lt;li&gt;&lt;a href="{{ request.get_full_path }}&amp;amp;selected_facets=location_exact:{{ level_study.0|urlencode }}"&gt;{{ level_study.0 }}&lt;/a&gt; ({{ level_study.1 }})&lt;/li&gt;
                      {% endfor %}
                      &lt;/ul&gt;
                  &lt;/div&gt;
              {% endif %}
  </code></pre>
  
  <p>How can I solve it to get those values?</p>