Schema Link
Assists with mocking and server-side rendering
Overview
The schema link provides a graphql execution environment, which allows you to perform GraphQL operations on a provided schema. This type of behavior is commonly used for server-side rendering (SSR) to avoid network calls and mocking data. While the schema link could provide graphql results on the client, currently the graphql execution layer is too heavy weight for practical application.
To unify your state management with client-side GraphQL operations, refer to Apollo Client's local state management functionality. It integrates with the Apollo Client cache and is much more lightweight.
Installation
npm install @apollo/client --save
Usage
Server Side Rendering
When performing SSR on the same server, you can use this library to avoid making network calls.
import { ApolloClient, InMemoryCache } from '@apollo/client';import { SchemaLink } from '@apollo/client/link/schema';import schema from './path/to/your/schema';const graphqlClient = new ApolloClient({cache: new InMemoryCache(),ssrMode: true,link: new SchemaLink({ schema })});
Mocking
For more detailed information about mocking, refer to the graphql-tools documentation.
import { ApolloClient, InMemoryCache } from '@apollo/client';import { SchemaLink } from '@apollo/client/link/schema';import { makeExecutableSchema, addMockFunctionsToSchema } from 'graphql-tools';const typeDefs = `Query {...}`;const mocks = {Query: () => ...,Mutation: () => ...};const schema = makeExecutableSchema({ typeDefs });const schemaWithMocks = addMockFunctionsToSchema({schema,mocks});const apolloCache = new InMemoryCache(window.__APOLLO_STATE__);const graphqlClient = new ApolloClient({cache: apolloCache,link: new SchemaLink({ schema: schemaWithMocks })});
Options
The SchemaLink constructor can be called with an object with the following properties:
| Option | Description |
|---|---|
schema | An executable graphql schema |
rootValue | The root value that is passed to the resolvers (i.e. the first parameter for the rootQuery) |
context | An object passed to the resolvers, following the graphql specification or a function that accepts the operation and returns the resolver context. The resolver context may contain all the data-fetching connectors for an operation. |
validate | Enable validation of incoming queries against the local schema before execution, returning validation errors in result.errors, just like a non-local GraphQL endpoint typically would. |