frankyang0529 / mongo-relay-connection

Assist building relay connection from mongoose.

Install

yarn add mongo-relay-connection graphql graphql-relay

graphql and graphql-relay are required as peer dependencies.

Overview

To assist building a Relay Connection type from a mongoose schema. It supports dynamic collection. The order could be based on a field that is not necessarily unique. And existing schema need not be changed at all.

It is based on the Relay pagination algorithm. But as including a value for both first and last is confusing, the last is ignored if both are given.

#	after	first	before	last	remarks	support
1					returns all	✓
2				✓		✓
3			✓			✓
4			✓	✓		✓
5		✓				✓
6		✓		✓	same as #5	✗
7		✓	✓			✓
8		✓	✓	✓	same as #7	✗
9	✓					✓
10	✓			✓		✓
11	✓		✓			✓
12	✓		✓	✓		✓
13	✓	✓				✓
14	✓	✓		✓	same as #13	✗
15	✓	✓	✓			✓
16	✓	✓	✓	✓	same as #15	✗

Usage

Suppose you want to do cursor based pagination over a collection:

// models/product.js

import mongoose, { Schema } from 'mongoose'

const ProductSchema = new Schema({
  name: String,
  type: String,
  price: Number
})

export default mongoose.model('Product', ProductSchema)

First create a corresponding GraphQLObjectType:

// types/product.js

import {
  GraphQLObjectType,
  GraphQLID,
  GraphQLString,
  GraphQLInt
} from 'graphql'

const Product = new GraphQLObjectType({
  name: 'Product',
  fields: {
    id: { type: GraphQLID },
    name: { type: GraphQLString },
    type: { type: GraphQLString },
    price: { type: GraphQLInt }
  }
})

export default Product

Then create your query by defining the type, args, and resolve function. Here all the food product is selected and sorted by price descendingly:

import {
  GraphQLObjectType
} from 'graphql'
import {
  mrType,
  mrArgs,
  mrResolve
} from 'mongo-relay-connection'
import Product from './types/product'
import ProductModel from './models/product'

const foodTypes = [
  "Bacon",
  "Cheese",
  "Chicken",
  "Chips",
  "Fish",
  "Pizza",
  "Salad",
  "Sausages",
  "Tuna"
]

const RootQuery = new GraphQLObjectType({
  name: 'RootQuery',
  fields: {
    allFoodProducts: {
      type: mrType('FoodProduct', Product),
      args: mrArgs,
      resolve (parentValue, args) {
        const query = {
          type: { $in: foodTypes }
        }
        const opts = {
          cursorField: 'price',
          direction: -1
        }
        return mrResolve(args, ProductModel, query, opts)
      }
    }
  }
})

export default RootQuery

Boom, you're done! No third step. All the hard work of resolving is done for you.

Limitation

It is based on sorting on a single given field (default is _id). If the field is not unique, it is compounded with _id as the secondary sort. So it could only be sorted in one given dimension.

License

MIT