Create a MongoDB projection from a GraphQL query

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300.1.27 years ago7 years agoMinified + gzip package size for graphql-projection in KB


Produces a MongoDB projection by parsing the GraphQL query in a resolve function to help to provide a concise query to MongoDB.


Install with yarn:
$ yarn add graphql-projection

or npm:
$ npm i -S graphql-projection

Now you can set create the projection function by feeding in your schema:
import makeProjector from 'graphql-projection';
import schema from './path/to/schema';

const projector = makeProjector(schema);

// ...

Basic Usage

In your resolve functions in your queries, you can use this function on the resolve info (the 4th argument to your resolve function) to produce a MongoDB projection:
// ...
      type: FoodType,
      args: {
        id: {
          name: 'ID of food to look up',
          type: new GraphQLNonNull(GraphQLInt),
      resolve: (root, { id }, request, resolveInfo) => {
        const projection = projector(resolveInfo);
        return db.collection('foods').find({ _id: id }, projection);
// ...

Custom Projections

Not all GraphQL fields will map 1-to-1 with their database counterparts. If you have a computed field, you can specify the projection that should be used for it by adding a projection property alongside the field's type definition:
const FoodType = new GraphQLObjectType({
  name: 'Food',
  fields: () => ({
    id: { type: new GraphQLNonNull(GraphQLInt) },
    name: { type: new GraphQLNonNull(GraphQLString) },
    reviews: { type: new GraphQLList(ReviewType) },
    averageRating: { type: new GraphQLNonNull(GraphQLInt), projection: 'reviews' },

Projection can either be an array of strings that will be added to the projection result (e.g., ['property_1', 'property_2', 'property_3']), or a space-separated string (e.g., 'property_1 property_2 property_3').


Pull requests are welcome. This project uses eslint to ensure a standardized code style, flow to take advantage of all of the flow types GraphQL exports, and Mocha+Chai for tests.