title: How can I update a graphql entry?
body: <p>I have a schema as follows:</p>
  
  <pre><code>type User @model {
    id: ID!
    firstName: String!
    lastName: String!
    locations: [Location]
  }
  
  type Location @model {
    id: ID!
    listOfPictures: [String]
    address: String!
    owner: User
  }
  </code></pre>
  
  <p>Currently I have entries to both Locations and Users.  The entries for my Locations are all null.
  I want to update one of my Locations, of ID '1234' to have the field 'owner' set to the User of ID '5678'.</p>
  
  <p>What is the correct syntax for this?  What do I have to enter into he Appsync console?</p>
  
  <p>Additionally, how could I update the 'locations' field of my User of id 'abc' model to add a Location, to the array of Locations, of Location with id 'def' ?
  Thanks.</p>