{
   "associations": {
     "title": "Associations",
     "children": ["one-to-one", "one-to-many","many-to-many", "polymorphic"]
   },
   "one-to-one":   { "title": "One-to-one" },
   "one-to-many":  { "title": "One-to-many" },
   "many-to-many": { "title": "Many-to-many" },
   "polymorphic": { "title": "Polymorphic" }
 }