Relay specification compliance in GraphQL

Introduction

Relay specification compliance helps organize data fetching in GraphQL so apps can load data efficiently and smoothly.

When building a React app that needs to fetch data in small chunks for faster loading.

When you want to handle large lists of items with smooth scrolling or pagination.

When you want to keep track of data changes and update the UI automatically.

When you want to standardize how your GraphQL server handles pagination and connections.

When you want to make your GraphQL API compatible with Relay clients.

Syntax

GraphQL

type Query {
  items(first: Int, after: String): ItemConnection
}

type ItemConnection {
  edges: [ItemEdge]
  pageInfo: PageInfo
}

type ItemEdge {
  node: Item
  cursor: String
}

type PageInfo {
  hasNextPage: Boolean
  endCursor: String
}

Relay uses a special pattern called 'connections' to handle lists and pagination.

The 'edges' hold the actual items and cursors to track position in the list.

Examples

Fetches the first 5 items after the position marked by 'cursor123', including info if more items exist.

GraphQL

query {
  items(first: 5, after: "cursor123") {
    edges {
      node {
        id
        name
      }
      cursor
    }
    pageInfo {
      hasNextPage
      endCursor
    }
  }
}

Defines a connection type for users following Relay's structure.

GraphQL

type UserConnection {
  edges: [UserEdge]
  pageInfo: PageInfo
}

type UserEdge {
  node: User
  cursor: String
}

Sample Program

This query fetches the first 3 books with their ids and titles, plus pagination info.

GraphQL

query {
  books(first: 3) {
    edges {
      node {
        id
        title
      }
      cursor
    }
    pageInfo {
      hasNextPage
      endCursor
    }
  }
}

Important Notes

Relay's cursor-based pagination helps avoid problems with changing data during paging.

Always include 'pageInfo' to know if more data can be fetched.

Cursors are opaque strings that mark positions in the list.

Summary

Relay specification organizes data fetching with connections and edges.

It uses cursors to paginate smoothly through lists.

Following Relay makes your GraphQL API compatible with Relay clients.