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README.md

graphql-parse-resolve-info

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Parses a GraphQLResolveInfo object into a tree of the fields that are being requested to enable optimisations to your GraphQL schema (e.g. to determine which fields are required from the SQL database).

Useful for optimising your GraphQL resolvers by allowing them to look ahead in the request, reducing the number of SQL queries or HTTP requests required to complete the GraphQL request.

Also provides a quick way to get the alias of the current field being resolved.

API

parseResolveInfo(resolveInfo)

Alias: parse

Gets the tree of subfields of the current field that is being requested, returning the following properties (recursively):

  • name: the name of the GraphQL field
  • alias: the alias this GraphQL field has been requested as, or if no alias was specified then the name
  • args: the arguments this field was called with; at the root level this will be equivalent to the args that the resolve(data, args, context, resolveInfo) {} method receives, at deeper levels this allows you to get the args for the nested fields without waiting for their resolvers to be called.
  • fieldsByTypeName: an object keyed by GraphQL object type names, where the values are another object keyed by the aliases of the fields requested with values of the same format as the root level (i.e. {alias, name, args, fieldsByTypeName}); see below for an example

Note that because GraphQL supports interfaces a resolver may return items of different types. For this reason, we key the fields by the GraphQL type name of the various fragments that were requested into the fieldsByTypeName field.

Once you know which specific type the result is going to be, you can then use this type (and its interfaces) to determine which sub-fields were requested - we provide a simplifyParsedResolveInfoFragmentWithType helper to aid you with this. In many cases you will know what type the result will be (because it can only be one type) so you will probably use this helper heavily.

Example usage:

const {
	parseResolveInfo,
	simplifyParsedResolveInfoFragmentWithType
} = require('graphql-parse-resolve-info');
// or import { parseResolveInfo, simplifyParsedResolveInfoFragmentWithType } from 'graphql-parse-resolve-info';

new GraphQLObjectType({
  name: ...
  fields: {
    ...
    foo: {
      type: new GraphQLNonNull(ComplexType),
      resolve(data, args, context, resolveInfo) {
        const parsedResolveInfoFragment = parseResolveInfo(resolveInfo);
        const { fields } = simplifyParsedResolveInfoFragmentWithType(
					parsedResolveInfoFragment,
					ComplexType
				);
        console.dir(fields);
        ...
      }
    }
  }
});

simplifyParsedResolveInfoFragmentWithType(parsedResolveInfoFragment, ReturnType)

Alias: simplify

Given an object of the form returned by parseResolveInfo(...) (which can be the root-level instance, or it could be one of the nested subfields) and a GraphQL type this method will return an object of the form above, with an additional field fields which only contains the fields compatible with the specified ReturnType.

Or, in other words, this simplifies the fieldsByTypeName to an object of only the fields compatible with ReturnType.

Example usage:

const {
	parseResolveInfo,
	simplifyParsedResolveInfoFragmentWithType
} = require('graphql-parse-resolve-info');

new GraphQLObjectType({
  name: ...
  fields: {
    ...
    foo: {
      type: new GraphQLNonNull(ComplexType),
      resolve(data, args, context, resolveInfo) {
        const parsedResolveInfoFragment = parseResolveInfo(resolveInfo);

        const { fields } = simplifyParsedResolveInfoFragmentWithType(
					parsedResolveInfoFragment,
					ComplexType
				);
        ...
      }
    }
  }
});

getAliasFromResolveInfo(resolveInfo)

Alias: getAlias

Returns the alias of the field being requested (or, if no alias was specified, then the name of the field).

Example:

const { getAliasFromResolveInfo } = require('graphql-parse-resolve-info');

new GraphQLObjectType({
  name: ...
  fields: {
    ...
    foo: {
      type: new GraphQLNonNull(GraphQLString),
      resolve(data, args, context, resolveInfo) {
        const alias = getAliasFromResolveInfo(resolveInfo);
        return alias;
      }
    }
  }
});

Example

For the following GraphQL query:

{
  allPosts {
    edges {
      cursor
      node {
        ...PostDetails
        author: personByAuthorId {
          firstPost {
            ...PostDetails
          }
          friends {
            nodes {
              ...PersonDetails
            }
            totalCount
            pageInfo {
              startCursor
            }
          }
        }
      }
    }
  }
}

fragment PersonDetails on Person {
  id
  name
  firstName
}

fragment PostDetails on Post {
  id
  headline
  headlineTrimmed
  author: personByAuthorId {
    ...PersonDetails
  }
}

The following resolver in the allPosts field:

const Query = new GraphQLObjectType({
  name: "Query",
  fields: {
    allPosts: {
      type: new GraphQLNonNull(PostsConnection),
      resolve(parent, args, context, resolveInfo) {
        const parsedResolveInfoFragment = parseResolveInfo(resolveInfo);
        const simplifiedFragment = simplifyParsedResolveInfoFragmentWithType(
          parsedResolveInfoFragment,
          resolveInfo.returnType
        );
        // ...
      },
    },

    // ...
  },
});

has parsedResolveInfoFragment:

{ alias: 'allPosts',
  name: 'allPosts',
  args: {},
  fieldsByTypeName:
   { PostsConnection:
      { edges:
         { alias: 'edges',
           name: 'edges',
           args: {},
           fieldsByTypeName:
            { PostsEdge:
               { cursor:
                  { alias: 'cursor',
                    name: 'cursor',
                    args: {},
                    fieldsByTypeName: {} },
                 node:
                  { alias: 'node',
                    name: 'node',
                    args: {},
                    fieldsByTypeName:
                     { Post:
                        { id: { alias: 'id', name: 'id', args: {}, fieldsByTypeName: {} },
                          headline:
                           { alias: 'headline',
                             name: 'headline',
                             args: {},
                             fieldsByTypeName: {} },
                          headlineTrimmed:
                           { alias: 'headlineTrimmed',
                             name: 'headlineTrimmed',
                             args: {},
                             fieldsByTypeName: {} },
                          author:
                           { alias: 'author',
                             name: 'personByAuthorId',
                             args: {},
                             fieldsByTypeName:
                              { Person:
                                 { id: { alias: 'id', name: 'id', args: {}, fieldsByTypeName: {} },
                                   name: { alias: 'name', name: 'name', args: {}, fieldsByTypeName: {} },
                                   firstName:
                                    { alias: 'firstName',
                                      name: 'firstName',
                                      args: {},
                                      fieldsByTypeName: {} },
                                   firstPost:
                                    { alias: 'firstPost',
                                      name: 'firstPost',
                                      args: {},
                                      fieldsByTypeName:
                                       { Post:
                                          { id: { alias: 'id', name: 'id', args: {}, fieldsByTypeName: {} },
                                            headline:
                                             { alias: 'headline',
                                               name: 'headline',
                                               args: {},
                                               fieldsByTypeName: {} },
                                            headlineTrimmed:
                                             { alias: 'headlineTrimmed',
                                               name: 'headlineTrimmed',
                                               args: {},
                                               fieldsByTypeName: {} },
                                            author:
                                             { alias: 'author',
                                               name: 'personByAuthorId',
                                               args: {},
                                               fieldsByTypeName:
                                                { Person:
                                                   { id: { alias: 'id', name: 'id', args: {}, fieldsByTypeName: {} },
                                                     name: { alias: 'name', name: 'name', args: {}, fieldsByTypeName: {} },
                                                     firstName:
                                                      { alias: 'firstName',
                                                        name: 'firstName',
                                                        args: {},
                                                        fieldsByTypeName: {} } } } } } } },
                                   friends:
                                    { alias: 'friends',
                                      name: 'friends',
                                      args: {},
                                      fieldsByTypeName:
                                       { PeopleConnection:
                                          { nodes:
                                             { alias: 'nodes',
                                               name: 'nodes',
                                               args: {},
                                               fieldsByTypeName:
                                                { Person:
                                                   { id: { alias: 'id', name: 'id', args: {}, fieldsByTypeName: {} },
                                                     name: { alias: 'name', name: 'name', args: {}, fieldsByTypeName: {} },
                                                     firstName:
                                                      { alias: 'firstName',
                                                        name: 'firstName',
                                                        args: {},
                                                        fieldsByTypeName: {} } } } },
                                            totalCount:
                                             { alias: 'totalCount',
                                               name: 'totalCount',
                                               args: {},
                                               fieldsByTypeName: {} },
                                            pageInfo:
                                             { alias: 'pageInfo',
                                               name: 'pageInfo',
                                               args: {},
                                               fieldsByTypeName:
                                                { PageInfo:
                                                   { startCursor:
                                                      { alias: 'startCursor',
                                                        name: 'startCursor',
                                                        args: {},
                                                        fieldsByTypeName: {} } } } } } } } } } } } } } } } } } },

and the simplified simplifiedFragment is the same as parsedResolveInfoFragment, but with the additional root-level property fields which compresses the root-level property fieldsByTypeName to a single-level object containing only the fields compatible with resolveInfo.returnType (in this case: only edges):

{ alias: 'allPosts',
  name: 'allPosts',
  args: {},
  fieldsByTypeName:
		...as before...
  fields:
   { edges:
      { alias: 'edges',
        name: 'edges',
        args: {},
        fieldsByTypeName:
           ...as before...

Thanks

This project was originally based on https://github.com/tjmehta/graphql-parse-fields, but has evolved a lot since then.