graph.cool two way bindings

Question

I am just starting with graph.cool, I am trying to build a graphql data modal with the help of graph.cool. It seems like we always need to make two way bindings. For example User -> Posts or Posts -> User.

I made a structure like this:

type User @model {
  id: ID! @isUnique
  name: String
  cart: Cart @relation(name: "UserCart")
}
type Category @model {
  id: ID! @isUnique
  name: String!
  image: String
  description: String
  subCategories: [SubCategory!]! @relation(name: "CategoriesSubCategories")
}
type SubCategory @model {
  id: ID! @isUnique
  name: String!
  products: [Product!]! @relation(name: "SubCategoryProduct")
  category: Category! @relation(name: "CategoriesSubCategories")
}

type Product @model {
  id: ID! @isUnique
  name: String
  image: String
  description: String
  basePrice: Int
  subCategory: SubCategory @relation(name: "SubCategoryProduct")
}

type Cart @model {
  id: ID! @isUnique
  cartItems: [CartItem!]! @relation(name: "CartItems")
  user: User! @relation(name: "UserCart")
}

type CartItem @model {
  id: ID! @isUnique
  quantity: Int
  #i need to do two way binding for this
  product: Product @relation(name: "CartItemProduct")
  # -----
  cart: Cart! @relation(name: "CartItems")
}

Everything is as expected. but when I created the cartItems, It has a property of Product and I don't know how to connect it with the user who created the cart. Help would be appreciated.

CartItem
    ✖ A relation directive with a name must appear exactly 2 times. Relation name: 'CartItemProduct'