eolas/Databases/GraphQL/Schema_Definition_Language.md

categories	tags
Databases	graphql

Schema Definition Language

SDL is the formal name for the syntax of GraphQL schemas.

Types

A schema is a collection of object types that contain fields. Each field has a type of its own. A field's type can be a primitive/scalar value (such as an Int or a String), or it can be another object type (just like a custom type in TS).

A schema's type can be non-nullable which is to say, a required field. We indicate this with !.

A type for a field can be a collection/array of a given type.

The following example indicates these properties:

type Person {
  age: Int
  name: String
  pets: [Pet]!
}

type Pet {
  species: String
  name: String
  age: Int
}

Queries

A query is also a schema type but of a special sort.

The fields of this type are entry points into the rest of the schema. These are the top-level fields that the client can query for.

For example if we had this type:

type Track {
  id: ID!
  title: String!
  author: Author!
  thumbnail: String
  length: Int
  modulesCount: Int
}

We could define a type to access a give Track as follows:

type Query {
  tracksForHomePage: [Track!]!
}

Then use this type as the basis for a query:

Descriptions

Descriptions are comments that allow you to document your Schema

Single line:

"Single line comment"

"""
Multi
line
comment
"""