Get parent object at field type policy

Question

Let's say that I have the following query that fetches a list of products.

query ProductList() {
  products() {
    name
    price
    stockQuantity
    isAvailable @client # This is a local-only field
  }
}

Also I have added a type policy for a local-only field at the in-memory cache creation, with a read function:

const cache = new InMemoryCache({
  typePolicies: { // Type policy map
    Product: {
      fields: { // Field policy map for the Product type
        isAvailable: { // Field policy for the isAvailable field
          read(existing, context) { // The read function for the isAvailable field
            // Return value
          }
        }
      }
    }
  }
});

How can I get the stockQuantity field of the parent Product object at the isAvailable read function?

Answer 1

const cache = new InMemoryCache({
  typePolicies: { // Type policy map
    Product: {
      fields: { // Field policy map for the Product type
        isAvailable: { // Field policy for the isAvailable field
          read(existing, {readField}) { // The read function for the isAvailable field
            const stockQuantity = readField("stockQuantity");
            return stockQuantity ? true : false;
          }
        }
      }
    }
  }
});