Graphql Fundamentals Notes

Links

What’s happening in index.js ?

const express = require("express")
const { graphqlHTTP } = require("express-graphql")

const schema = require("./schema/schema")
const app = express()

// express-graphql middlewear
app.use(
  "/graphql",
  graphqlHTTP({
    graphiql: true,
    schema,
  })
)

app.listen(4000, () => {
  console.log("lift off")
})
  • Meaning you can access the Graphiql UI @localhost:4000/graphql

Root query in schema.js

  • your entry point when querying a graph. this is where the traversal starts.

Types

  • Scalar types: Single data type, similar to what primitives would be, in other languages. String, int, Float, Bool, ID

example: User Type

// Create types
const UserType = new GraphQLObjectType({
  name: "User",
  description: "Is a human being. or is it?",
  fields: () => ({
    id: { type: GraphQLID },
    name: { type: GraphQLString },
    age: { type: GraphQLInt },
    profession: { type: GraphQLString },

    posts: {
      type: new GraphQLList(PostType),
      resolve(parent, args) {
        return _.filter(postsData, { userId: parent.id })
      },
    },

    hobbies: {
      type: new GraphQLList(HobbyType),
      resolve(parent, args) {
        return _.filter(hobbiesData, { userId: parent.id })
      },
    },
  }),
})

  • Note that the fields posts & hobbies have hand-written resolvers

  • the underscore _ is lodash

  • UserType fields makes use of scalar types on the id, name, age, & profession.

  • Non-nullable Types:

    comment: { type: new GraphQLNonNull(GraphQLString) },
  • Object Types:
    • Do you notice the relational aspect of it? the type used for posts is defined elsewhere, but refered to by this line type: new GraphQLList(PostType)
    hobbies: {
        type: new GraphQLList(HobbyType),
        resolve(parent, args) {
        return _.filter(hobbiesData, { userId: parent.id })
        },
    },

What mutations look like

  • These also exist in schema.js
  • Exported alongside the RootQuery

Mutation object snippet

const Mutation = new GraphQLObjectType({
  name: "Mutation",
  fields: {
    createUser: {
      type: UserType,
      args: {
        name: { type: GraphQLString },
        age: { type: GraphQLInt },
        profession: { type: GraphQLString },
      },

      resolve(parent, args) {
        let user = {
          name: args.name,
          age: args.age,
          profession: args.profession,
        }

        return user
      },
    },
  }
})
  • All mutation definitions live in a single Mutation object, specifically under the fields key.
module.exports = new GraphQLSchema({
  query: RootQuery,
  mutation: Mutation,
})