title: How do I mutate existing data with GraphQL, Graphene and Relay?
body: <p>I feel like it should be documented somewhere but I cant find it. I can add data to my db with a mutation but I cant change it.</p>
  
  <p>Graphene works with Django and my db is SQLite</p>
  
  <p>Its quite specific, I hope someone knows the answer. Among other things I tried:</p>
  
  <pre><code>mutation AppMutation(
    $input: AddSchoolNodeInput!
    ) {
      addSchool(input: $input) {
        school {
          id
          name
          description
       }     
      }
    }
  </code></pre>
  
  <p>where <code>AddSchoolNodeInput!</code> is (<code>"U2Nob29sTm9kZToxMQ=="</code> is an existing id): </p>
  
  <pre><code>{
    "name": "edit kaas", 
    "description": "edit fails",
    "clientMutationId":"U2Nob29sTm9kZToxMQ=="
   } 
  </code></pre>
  
  <p>it create a new item and returns this:</p>
  
  <pre><code>{
    "data": {
      "addSchool": {
        "school": {
          "id": "U2Nob29sTm9kZToxNA==",
          "name": "edit kaas",
          "description": "edit fails"
        }
      }
    }
  }
  </code></pre>