Return Value

Return Value

Schema of primitive type query should be returning the entire (full integrity) of a node. e.g. Book should return all fields relevant to Book node.

Schema can define a field as required in the query, but it is possible the server side may have defined it as any arbitrary return value.

  • For example, when a field is required, but a server side hasn't completed implementation, the server side could have defined it to return null or undefined despite the interface definition

This way, the type is spoofed

null is an explicit return that the field exists and the record is empty (nullable type).

undefined

GraphQL typically treats undefined in resolvers as a signal that the field does not exist, and it may result in an error or unexpected behavior depending on the GraphQL server you are using (e.g., Apollo Server, GraphQL.js).

Every Query is its own type

Every Query is its own type

  • Use the type that is delivered

Caveat with required fields

When you require a field that is a primitive type, be aware that primitive type on the field may have its required fields that are another primitive type (effectively, creating a complex and deep chain of required fields to satisfy the type expectation from codegen)

Required/Non-nullable Fields (!)

Non-nullable field means that our server always expects to return a non-null value for the defined field.

type Author {
    name: String! # Can't return null
    books: [Book]
}

If the field ends up returning a null value from resolver function, GraphQL will trigger a GraphQL execution error, letting the client know that something has gone wrong.

Non-nullable field also applies to a list.

type Author {
  books: [Book!]! # This list can't be null AND its list *items* can't be null
}

If the ! is inside the array, the list can't include items that are null.

If the ! is outside the array, the list itself can't be null.

[Node]
# [], null, [null], and [{field: "someVal"}]

[Node!]
# [], null, [{field: "someVal"}]

[Node]!
# [], [null], [{field: "someVal"}]

[Node!]!
# [], [{field: "someVal"}]