graphql-fields

What is graphql-fields?

The graphql-fields npm package is a utility for extracting the fields requested in a GraphQL query. It helps in resolving only the necessary fields, optimizing the performance of your GraphQL server by avoiding over-fetching data.

What are graphql-fields's main functionalities?

Extracting Fields from a GraphQL Query

This feature allows you to extract the fields requested in a GraphQL query. By using the `graphqlFields` function and passing the `info` object from the resolver, you can get an object representing the fields requested. This can be used to optimize data fetching by only querying the necessary fields from your data source.

const graphqlFields = require('graphql-fields');

const resolvers = {
  Query: {
    user: (parent, args, context, info) => {
      const fields = graphqlFields(info);
      console.log(fields); // Logs the fields requested in the query
      // Fetch and return the user data based on the requested fields
    }
  }
};

Handling Nested Fields

This feature allows you to handle nested fields in a GraphQL query. The `graphqlFields` function will return an object that includes nested fields, enabling you to understand the full structure of the query and fetch data accordingly.

const graphqlFields = require('graphql-fields');

const resolvers = {
  Query: {
    user: (parent, args, context, info) => {
      const fields = graphqlFields(info);
      console.log(fields); // Logs nested fields as well
      // Fetch and return the user data based on the requested fields
    }
  }
};

Other packages similar to graphql-fields

graphql-parse-resolve-info

The graphql-parse-resolve-info package provides similar functionality by parsing the resolve info to extract the fields requested in a GraphQL query. It offers more detailed information about the query, including arguments and fragments, making it a more comprehensive solution compared to graphql-fields.

README

graphql-fields

Turns GraphQLResolveInfo into a map of the requested fields. Flattens all fragments and duplicated fields into a neat object to easily see which fields were requested at any level. Takes into account any @include or @skip directives, excluding fields/fragments which are @include(if: $false) or @skip(if: $true).

Usage

Schema Type definition

const graphqlFields = require('graphql-fields');
const graphql = require('graphql')

const UserType = new graphql.GraphQLObjectType({
    name: 'User',
    fields: {
        profile: {type: new graphql.GraphQLObjectType({
          name: 'Profile',
          fields: {
            firstName: {type: graphql.GraphQLString},
            lastName: {type: graphql.GraphQLString},
            middleName: {type: graphql.GraphQLString},
            nickName: {type: graphql.GraphQLString},
            maidenName: {type: graphql.GraphQLString}
          }
        }),
        email: {type: graphql.GraphQLString},
        id: {type: graphql.GraphQLID}
    }
});

module.exports = new GraphQLSchema({
    query: new GraphQLObjectType({
        name: 'Query',
        fields: () =>
            Object.assign({
                user: {
                    type: UserType,
                    resolve(root, args, context, info) {
                        console.log(
                            JSON.stringify(graphqlFields(info), null, 2);
                        );
                        ...
                    }
                }
            })
    })
})

Query

{
  user {
    ...A
    profile {
      ...B
      firstName
    }
  }
}

fragment A on User {
  ...C
  id,
  profile {
    lastName
  }
}

Fragment B on Profile {
  firstName
  nickName @skip(if: true)
}

Fragment C on User {
  email,
  profile {
    middleName
    maidenName @include(if: false)
  }
}

will log

{
  "profile": {
    "firstName": {},
    "lastName": {},
    "middleName": {}
  },
  "email": {},
  "id": {}
}

subfields arguments

To enable subfields arguments parsing, you'll have to provide an option object to the function. This feature is disable by default.

const graphqlFields = require('graphql-fields');
const fieldsWithSubFieldsArgs = graphqlFields(info, {}, { processArguments: true });

For each subfield w/ arguments, a __arguments property will be created. It will be an array with the following format:

[
    {
        arg1Name: {
            kind: ARG1_KIND,
            value: ARG1_VALUE,
        },
    },
    {
        arg2Name: {
            kind: ARG2_KIND,
            value: ARG2_VALUE,
        }
    }
]

The kind property is here to help differentiate value cast to strings by javascript clients, such as enum values.

Exclude specific fields

Most of the time we don't need __typename to be sent to backend/rest api, we can exclude __typename using this:

const graphqlFields = require('graphql-fields');
const fieldsWithoutTypeName = graphqlFields(info, {}, { excludedFields: ['__typename'] });

Why

An underlying REST api may only return fields based on query params.

{
  user {
    profile {
      firstName
    },
    id
  }
}

should request /api/user?fields=profile,id

while

{
  user {
    email
  }
}

should request /api/user?fields=email

Implement your resolve method like so:

resolve(root, args, context, info) {
    const topLevelFields = Object.keys(graphqlFields(info));
    return fetch(`/api/user?fields=${topLevelFields.join(',')}`);
}

Tests

npm test