Explain GraphQL code

What this GraphQL sample shows

fields

A query lists the fields it wants, and the reply has the same shape with only those fields. Run against a test schema, each order came back with just id, total, customer.name and items; asking for only id returned { "id": "1001" } and nothing else.

variables and defaults

$status and $first are filled in from a separate JSON object sent with the query. Int! means required, and = OPEN is a default: with only {"first": 2}, the reply held two open orders, 1001 and 1003, and skipped the shipped 1002. Sending "status": "SHIPPED" returned 1002.

arguments

Values in parentheses after a field, such as orders(status: $status, first: $first), are arguments the server uses to pick what to return. Here they filter by status and cap how many orders come back.

fragments

fragment UserBits on User is a reusable list of fields for a User, and ...UserBits pastes it in. me came back with name and email, as if they were written there.

Good to know

• Run with graphql-js 17.0.2 against a small test schema of orders, items and users, with made-up data.
• The server checks every field name: asking for price gave Cannot query field "price" on type "Order".
• A field that holds an object needs its own list of fields. customer on its own gave Field "customer" of type "User!" must have a selection of subfields. Did you mean "customer { ... }"?
• A field without ! in the schema can come back null: the second customer's email did.

Watch out: A required variable left out stops the whole query. Sent without $first, it returned no data, only Variable "$first" has invalid value: Expected a value of non-null type "Int!" to be provided. Enum values are case-sensitive too: "shipped" was refused with Did you mean the enum value "SHIPPED"?