title: Active Model Serializers has_many associations
body: <p>I'm using the gem <a href="https://github.com/rails-api/active_model_serializers" rel="noreferrer"><strong><code>active_model_serializers</code></strong></a>.</p>
  
  <p><strong>Serializers:</strong></p>
  
  <pre><code>class ProjectGroupSerializer &lt; ActiveModel::Serializer
    attributes :id, :name, :description
    has_many :projects
  end
  
  class ProjectSerializer &lt; ActiveModel::Serializer
    attributes :id, :name, :description
    belongs_to :project_group
  end
  </code></pre>
  
  <p><strong>Controller:</strong></p>
  
  <pre><code>def index
    @project_groups = ProjectGroup.all.includes(:projects)
    render json: @project_groups, include: 'projects'
  end
  </code></pre>
  
  <p>I'm getting the following <strong>response</strong>:</p>
  
  <pre><code>{
    "data": [
      {
        "id": "35",
        "type": "project_groups",
        "attributes": {
          "name": "sdsdf",
          "description": null
        },
        "relationships": {
          "projects": {
            "data": [
              {
                "id": "1",
                "type": "projects"
              },
              {
                "id": "2",
                "type": "projects"
              }
            ]
          }
        }
      }
    ],
    "included": [
      {
        "id": "1",
        "type": "projects",
        "attributes": {
          "name": "qweqwe",
          "description": null,
          "project_group_id": 1
        },
        "relationships": {
          "project_group": {
            "data": {
              "id": "1",
              "type": "project_groups"
            }
          }
        }
      },
      {
        "id": "2",
        "type": "projects",
        "attributes": {
          "name": "ewe",
          "description": null,
          "project_group_id": 2
        },
        "relationships": {
          "project_group": {
            "data": {
              "id": "2",
              "type": "project_groups"
            }
          }
        }
      }
    ]
  }
  </code></pre>
  
  <p>I want to retrieve the associations inside the <strong>relationships</strong> <em>object</em>, not <em>outside</em> (in <code>included</code> <code>array</code>) as in the response that I'm receiving. Is it possible?</p>
  
  <p>PS1: <strong>belongs_to</strong> associations works fine, the associations comes inside the <strong>relationships</strong> <em>object</em>, as in docs.</p>
  
  <p>PS2: I want to do this because I have 3 or 4 associations and I want to access them from each object. This way that I'm getting the response will be a real mess.</p>