Mercurius Dynamic Schema

A plugin for Fastify allowing serving a different schema per request path.

Note: persisted queries are currently not supported.

Table of contents

• Installation
• Quickstart
• Options
• License

Installation

npm i fastify mercurius-dynamic-schema

Quickstart

const Fastify = require("fastify");
const mercuriusDynamicSchema = require("mercurius-dynamic-schema");

const app = Fastify({
  logger: true
})

const schema1 = `
    type Query {
      add(x: Int, y: Int): Int
    }
  `

const resolvers1 = {
  Query: {
    add: async (_, obj) => {
      const { x, y } = obj
      return x + y
    }
  }
}

const schema2 = `
    type Query {
      subtract(x: Int, y: Int): Int
    }
  `

const resolvers2 = {
  Query: {
    subtract: async (_, obj) => {
      const { x, y } = obj
      return x - y
    }
  }
}

app.register(mercuriusDynamicSchema, {
  schemas: [
    {
      name: 'schema1',
      schema: schema1,
      resolvers: resolvers1,
    },
    {
      name: 'schema2',
      schema: schema2,
      resolvers: resolvers2
    }
  ],
  strategy: req => {
    return req.headers?.schema || 'schema1'
  },
  context: req => {
    return { add: req.headers.add }
  }
})

app.listen({ port: 3000 })

Then you can start the server using Node.js and you can send HTTP request using curl:

curl -X POST \
     -H 'content-type: application/json' \
     -d '{ "query": "{ add(x: 2, y: 2) }" }' \
     localhost:3000/graphql

Response: 
{"data":{"add":4}}

curl -X POST \
     -H 'content-type: application/json' \
     -H 'schema: schema2' \
     -d '{ "query": "{ subtract(x: 2, y: 1) }" }' \
     localhost:3000/graphql

Response:
{"data":{"subtract":1}}

In the fist request, we're not specifying the schema header, so we will use the default one (schema1 as defined in the code above).

Options

You can pass the following options when registering the plugin (all of them are optional unless stated otherwise):

Parameter	Type	Description
schemas (required)	{ name: string; path?: string; resolvers: IResolvers, schema: string ()}[]	An array of dynamic schema definitions (see details below).
strategy (required)	req => string	A function that returns a strategy name from a request object. This function will get the value of the constraint from each incoming request, and is used in deriveConstraint of fastify's addConstraintStrategy
context	req => string	A function that returns a context object based on the request. See Mercurius Context for reference.

schemas

Each schema definition uses the following properties

prop	required	default	description
name	yes		a unique name across all schema definitions
schema	yes		the GraphQL schema
resolvers	yes		the resolvers corresponding to the schema defined above
path	no	/graphql	the route at which these schema and resolvers will be available

strategy

Example: this will return the value of a header named schema, or default to schema1

  req => {
    return req.headers?.schema || 'schema1'
  }

context

Example: this will pass a context containing a prop named add, which has the value from a header name add. Inside the resolver than we can read the add property using ctx.add where ctx is the context object in the resolver.

  req => {
    return { add: req.headers.add }
  }

This project also contains

• code linting with ESlint and prettier
• pre-commit code linting and commit message linting with husky and commitlint
• dependabot setup with automatic merging thanks to "merge dependabot" GitHub action
• notifications about commits waiting to be released thanks to "notify release" GitHub action
• PRs' linked issues check with "check linked issues" GitHub action
• Continuous Integration GitHub workflow

License

MIT