84 lines
1.4 KiB
Markdown
84 lines
1.4 KiB
Markdown
---
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categories:
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- Databases
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tags: [graphql]
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---
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# Schema Definition Language
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SDL is the formal name for the syntax of GraphQL schemas.
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## Types
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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).
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A schema's type can be non-nullable which is to say, a required field. We indicate this with `!`.
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A type for a field can be a collection/array of a given type.
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The following example indicates these properties:
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```gql
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type Person {
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age: Int
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name: String
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pets: [Pet]!
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}
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type Pet {
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species: String
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name: String
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age: Int
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}
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```
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## Queries
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A query is also a schema type but of a special sort.
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> 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.
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For example if we had this type:
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```graphql
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type Track {
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id: ID!
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title: String!
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author: Author!
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thumbnail: String
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length: Int
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modulesCount: Int
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}
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```
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We could define a type to access a give `Track` as follows:
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```graphql
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type Query {
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tracksForHomePage: [Track!]!
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}
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```
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Then use this type as the basis for a query:
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```
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```
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## Descriptions
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Descriptions are comments that allow you to document your Schema
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Single line:
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```gql
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"Single line comment"
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```
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```gql
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"""
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Multi
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line
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comment
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"""
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```
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