Using GraphQL Fragments

Fragments allow you to reuse parts of GraphQL queries. It also allows you to split up complex queries into smaller, easier to understand components.

The building blocks of a fragment

Here is an example fragment:

graphql

fragment FragmentName on TypeName {
  field1
  field2
}

A fragment consists of three components:

FragmentName: the name of the fragment that will be referenced later.
TypeName: the GraphQL type of the object the fragment will be used on. This is important because you can only query for fields that actually exist on a given object.
The body of the query. You can define any fields with any level of nesting in here, the same that you would elsewhere in a GraphQL query

Creating and using a fragment

A fragment can be created inside any GraphQL query, but it's good practice to create the query separately. More organization advice in the Conceptual Guide.

jsx:title=src/components/IndexPost.jsx

import React from "react"
import { graphql } from "gatsby"

export default function IndexPost( props ) {
  return (...)
}

export const query = graphql`
  fragment SiteInformation on Site {
    siteMetadata {
      title
      siteDescription
    }
  }
`

This defines a fragment named SiteInformation. Now it can be used from within the page's GraphQL query:

jsx:title=src/pages/main.jsx

import React from "react"
import { graphql } from "gatsby"
import IndexPost from "../components/IndexPost"

export default function Main({ data }) {
  return (
    <div>
      <h1>{data.site.siteMetadata.title}</h1>
      <p>{data.site.siteMetadata.siteDescription}</p>

      {/*
        Or you can pass all the data from the fragment
        back to the component that defined it
      */}
      <IndexPost siteInformation={data.site.siteMetadata} />
    </div>
  )
}

export const query = graphql`
  query {
    site {
      ...SiteInformation
    }
  }
`

When compiling your site, Gatsby preprocesses all GraphQL queries it finds. Therefore, any file that gets included in your project can define a snippet. However, only Pages can define GraphQL queries that actually return data. This is why you can define the fragment in the component file - it doesn't actually return any data directly.

The building blocks of a fragment

Creating and using a fragment

Further reading