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 backend).
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.
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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 fieldalias: the alias this GraphQL field has been requested as, or if no alias was specified then thenameargs: the arguments this field was called with; at the root level this will be equivalent to theargsthat theresolve(data, args, context, resolveInfo) {}method receives, at deeper levels this allows you to get theargsfor 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);
...
}
}
}
});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
);
...
}
}
}
});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;
}
}
}
});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...This project was originally based on https://github.com/tjmehta/graphql-parse-fields, but has evolved a lot since then.