About GraphQL
GraphQL is different from REST: it has a schema and a type system. GraphQL is also not that different from REST: requests and responses are JSON.
Terms
Schema
The schema defines what data can be accessed, so-called objects and fields. Requests are validated (opens in a new tab) and executed (opens in a new tab) against the schema. You can view the schema using so-called schema introspection. You can perform an introspection manually (opens in a new tab) by querying the schema itself, or by using a GraphQL tool with a schema browser. You can use these tools to discover the API’s possibilities. Some of these tools are:
Fields
A field is a piece of data you can retrieve from an object. This can be another object, or a scalar value.
The official spec (opens in a new tab) about fields:
All GraphQL operations must specify their selections down to fields which return scalar values to ensure an unambiguously shaped response.
This means you must add nested fields until all fields return scalars.
Queries
Queries can be considered functions you can call to retrieve data. A query is an entrypoint to the schema.
Mutations
Mutations can be considered function you can call to send data.
Argument
Some fields require arguments. For example, most mutations use arguments to allow you to specify what data to store.
Union
Most queries and mutations can return multiple types of result, a so-called union. Unions allow you to distinguish between these different types of result. We primarily use this for error handling.