graphql-query-language-breakdown.md

Diagnose GraphQL query language

• In a GraphQL service we define our schema and then the incoming requests will be validated against it.
• Approaches in defining the schema:
  • All-in-One Definition: define the schema directly in your code.
  • Using Schema Definition Language (SDL): define schema in a separate file.
  • Schema inferred from code: you have resolvers annotated with decorators, then a lib will generate the schema based on your code.
  • Infer schema and resolver from the underlying database.

Jargons

GraphQL Object type

A type with some fields.

Field

Fields that can appear in any part of a GraphQL query that operates on the Character type.

List type

An array of the specified type.

Cannot define a non-empty list (an array with at least one member).

A type modifier.

Non-Null type

The GraphQL service promises to give you a value whenever you query this field.

A type modifier.

Argument

Arguments in GraphQL are passed by name specifically. Order does not matter!

All arguments are named.

Every field on a GraphQL Object type can have zero or more arguments.

Can be required or optional.

Tip

[type] VS [type]! VS [type!] VS [type!]!

The Query, Mutation, and Subscription types

Important

• Every GraphQL schema must support query operations.
• The entry point of a "root" operation type is a regular Object type called Query by default.

• Query, Mutation, and Subscription are entry points of my GraphQL API.

  • Note that they should start with a capital letter and the same name as they are listed here.

  • If you want to use a custom name, you can do it. But then you need to tell GraphQL about it:

    type MySubscriptionType {
      todoStatusChange: Todo!
    }
    type MyMutationType {
      createTodo: Todo!
    }
    type MyQueryType {
      getTodos: [Todo]
    }
    schema {
      query: MyQueryType
      mutation: MyMutationType
      subscription: MySubscriptionType
    }

    Learn more about Subscription here