How to connect GraphQL and PostgreSQL

问题:

GraphQL has mutations, Postgres has INSERT; GraphQL has queries, Postgres has SELECT's; etc., etc.. I haven't found an example showing how you could use both in a project, for example passing all the queries from front end (React, Relay) in GraphQL, but to a actually store the data in Postgres.

Does anyone know what Facebook is using as DB and how it's connected with GraphQL?

Is the only option of storing data in Postgres right now to build custom "adapters" that take the GraphQL query and convert it into SQL?

回答1:

GraphQL is database agnostic, so you can use whatever you normally use to interact with the database, and use the query or mutation's resolve method to call a function you've defined that will get/add something to the database.

Without Relay

Here is an example of a mutation using the promise-based Knex SQL query builder, first without Relay to get a feel for the concept. I'm going to assume that you have created a userType in your GraphQL schema that has three fields: id, username, and created: all required, and that you have a getUser function already defined which queries the database and returns a user object. In the database I also have a password column, but since I don't want that queried I leave it out of my userType.

// db.js
// take a user object and use knex to add it to the database, then return the newly
// created user from the db.
const addUser = (user) => (
  knex('users')
  .returning('id') // returns [id]
  .insert({
    username: user.username,
    password: yourPasswordHashFunction(user.password),
    created: Math.floor(Date.now() / 1000), // Unix time in seconds
  })
  .then((id) => (getUser(id[0])))
  .catch((error) => (
    console.log(error)
  ))
);

// schema.js
// the resolve function receives the query inputs as args, then you can call
// your addUser function using them
const mutationType = new GraphQLObjectType({
  name: 'Mutation',
  description: 'Functions to add things to the database.',
  fields: () => ({
    addUser: {
      type: userType,
      args: {
        username: {
          type: new GraphQLNonNull(GraphQLString),
        },
        password: {
          type: new GraphQLNonNull(GraphQLString),
        },
      },
      resolve: (_, args) => (
        addUser({
          username: args.username,
          password: args.password,
        })
      ),
    },
  }),
});

Since Postgres creates the id for me and I calculate the created timestamp, I don't need them in my mutation query.

The Relay Way

Using the helpers in graphql-relay and sticking pretty close to the Relay Starter Kit helped me, because it was a lot to take in all at once. Relay requires you to set up your schema in a specific way so that it can work properly, but the idea is the same: use your functions to fetch from or add to the database in the resolve methods.

One important caveat is that the Relay way expects that the object returned from getUser is an instance of a class User, so you'll have to modify getUser to accommodate that.

The final example using Relay (fromGlobalId, globalIdField, mutationWithClientMutationId, and nodeDefinitions are all from graphql-relay):

/**
 * We get the node interface and field from the Relay library.
 *
 * The first method defines the way we resolve an ID to its object.
 * The second defines the way we resolve an object to its GraphQL type.
 *
 * All your types will implement this nodeInterface
 */
const { nodeInterface, nodeField } = nodeDefinitions(
  (globalId) => {
    const { type, id } = fromGlobalId(globalId);
    if (type === 'User') {
      return getUser(id);
    }
    return null;
  },
  (obj) => {
    if (obj instanceof User) {
      return userType;
    }
    return null;
  }
);

// a globalId is just a base64 encoding of the database id and the type
const userType = new GraphQLObjectType({
  name: 'User',
  description: 'A user.',
  fields: () => ({
    id: globalIdField('User'),
    username: {
      type: new GraphQLNonNull(GraphQLString),
      description: 'The username the user has selected.',
    },
    created: {
      type: GraphQLInt,
      description: 'The Unix timestamp in seconds of when the user was created.',
    },
  }),
  interfaces: [nodeInterface],
});

// The "payload" is the data that will be returned from the mutation
const userMutation = mutationWithClientMutationId({
  name: 'AddUser',
  inputFields: {
    username: {
      type: GraphQLString,
    },
    password: {
      type: new GraphQLNonNull(GraphQLString),
    },
  },
  outputFields: {
    user: {
      type: userType,
      resolve: (payload) => getUser(payload.userId),
    },
  },
  mutateAndGetPayload: ({ username, password }) =>
    addUser(
      { username, password }
    ).then((user) => ({ userId: user.id })), // passed to resolve in outputFields
});

const mutationType = new GraphQLObjectType({
  name: 'Mutation',
  description: 'Functions to add things to the database.',
  fields: () => ({
    addUser: userMutation,
  }),
});

const queryType = new GraphQLObjectType({
  name: 'Query',
  fields: () => ({
    node: nodeField,
    user: {
      type: userType,
      args: {
        id: {
          description: 'ID number of the user.',
          type: new GraphQLNonNull(GraphQLID),
        },
      },
      resolve: (root, args) => getUser(args.id),
    },
  }),
});

回答2:

We address this problem in Join Monster, a library we recently open-sourced to automatically translate GraphQL queries to SQL based on your schema definitions.

回答3:

This GraphQL Starter Kit can be used for experimenting with GraphQL.js and PostgreSQL:

https://github.com/kriasoft/graphql-starter-kit - Node.js, GraphQL.js, PostgreSQL, Babel, Flow

(disclaimer: I'm the author)

回答4:

Have a look at graphql-sequelize for how to work with Postgres.

For mutations (create/update/delete) you can look at the examples in the relay repo for instance.

回答5:

Postgraphile https://www.graphile.org/postgraphile/ is Open Source

Rapidly build highly customisable, lightning-fast GraphQL APIs

PostGraphile is an open-source tool to help you rapidly design and serve a high-performance, secure, client-facing GraphQL API backed primarily by your PostgreSQL database. Delight your customers with incredible performance whilst maintaining full control over your data and your database. Use our powerful plugin system to customise every facet of your GraphQL API to your liking.

回答6:

Probably FB using mongodb or nosql in backend. I've recently read a blog entry which explain how to connect to mongodb. Basically, you need to build a graph model to match the data you already have in your DB. Then write resolve, reject function to tell GQL how to behave when posting a query request.

See https://www.compose.io/articles/using-graphql-with-mongodb/

回答7:

Have a look at SequelizeJS which is a promise based ORM that can work with a number of dialects; PostgreSQL, MySQL, SQLite and MSSQL

The below code is pulled right from its example

const Sequelize = require('sequelize');
const sequelize = new Sequelize('database', 'username', 'password', {
  host: 'localhost',
  dialect: 'mysql'|'sqlite'|'postgres'|'mssql',

  pool: {
    max: 5,
    min: 0,
    acquire: 30000,
    idle: 10000
  },

  // SQLite only
  storage: 'path/to/database.sqlite',

  // http://docs.sequelizejs.com/manual/tutorial/querying.html#operators
  operatorsAliases: false
});

const User = sequelize.define('user', {
  username: Sequelize.STRING,
  birthday: Sequelize.DATE
});

sequelize.sync()
  .then(() => User.create({
    username: 'janedoe',
    birthday: new Date(1980, 6, 20)
  }))
  .then(jane => {
    console.log(jane.toJSON());
  });