title: Loopback.io belongsTo in REST
body: <p>I'm a bit confused about the belongsTo relation function of loopback.io</p>
  
  <p>So let's take the following example:</p>
  
  <p>I have a model called <strong>Project</strong> which has a relation to a <strong>Customer</strong> object. So a Project belongs to a Customer.</p>
  
  <p>This is my Project model</p>
  
  <pre><code>{
    "name": "Project",
    "plural": "Projects",
    "base": "PersistedModel",
    "strict": false,
    "idInjection": false,
    "options": {
      "validateUpsert": true
    },
    "properties": {
      "title": {
        "type": "string",
        "required": true
      },
      "description": {
        "type": "string"
      },
      "dateCreated": {
        "type": "date"
      }
    },
    "validations": [],
    "relations": {
      "customer": {
        "type": "belongsTo",
        "model": "Customer",
        "foreignKey": "customerId"
      }
    },
    "acls": [],
    "methods": {}
  }
  </code></pre>
  
  <p>So when I run the app and I go to <a href="http://0.0.0.0:3000/explorer" rel="nofollow">http://0.0.0.0:3000/explorer</a> I can see the API. But When I go to project I only see </p>
  
  <pre><code> GET /Projects/{id}/customer     Fetches belongsTo relation customer.
  </code></pre>
  
  <p>I was also expecting other functions like</p>
  
  <pre><code> POST /Projects/{id}/customer 
   DELETE /Projects/{id}/customer 
  </code></pre>
  
  <p>Why are they not available here? Or how can I set the customer for a project via REST API?</p>