GraphQL Node.js: determine what types are used within a query

Question

Given I have a schema that has types: User, Comment, Post, Image; Is it possible to determine the GraphQL types being used in a query, given the query and schema? eg if a client had a query

{
    user(userName: "username") {
        email
        comments
    }
}

In this case, the query has types User and Comment. Is it possible to determine the programmatically using either the graphql-js or graphql packages for node.js?

Answer 1

For anyone else who runs into this, I found the answer in visit and TypeInfo Here's a function that takes the GraphQL query (document) and a schema and returns which data types from the schema are being used.

import { visit } from 'graphql/language/visitor'
import { parse } from 'graphql/language'
import { TypeInfo, visitWithTypeInfo } from 'graphql'
import { schema as _schema } from '../src/schema/schema'

const getQueryTypes = (schema, query) => {
    const typeInfo = new TypeInfo(schema)
    var typesMap = {}
    var visitor = {
        enter(node) {
            typeInfo.enter(node)
            typesMap[typeInfo.getType()] = true
        },
        leave(node) {
            typesMap[typeInfo.getType()] = true
            typeInfo.leave(node)
        }
    }
    visit(parse(query), visitWithTypeInfo(typeInfo, visitor))
    return Object.keys(typesMap)
}

const _query = `
    query {
        ...
    } 
`

console.log(getQueryTypes(_schema, _query))

Answer 2

You have to create types using GraphQLObjectType , for example:

export default new GraphQLObjectType(
  ({
    name: 'User',
    description: 'Represents a User',
    fields: () => ({
      _id: {
        type: GraphQLNonNull(GraphQLString),
        resolve: user => user._id,
      },
      name: {
        type: GraphQLNonNull(GraphQLString),
        description: 'Name of the user',
        resolve: user => user.name,
      },
      createdAt: {
        type: GraphQLString,
        description: '',
        resolve: user => user.createdAt.toISOString(),
      },
      updatedAt: {
        type: GraphQLString,
        description: '',
        resolve: user => user.updatedAt.toISOString(),
      },
    }),
  }: GraphQLObjectTypeConfig<User, GraphQLContext>),
);

Then you can use this UserType on another type, by declaring type: GraphQLNonNull(UserType) for example.

https://graphql.org/graphql-js/constructing-types/

Hope it helps :)

Answer 3

Given a valid document string representing some GraphQL operation, you can parse the string into an AST.

import { parse, validate } from 'graphql' 

const document = parse(someDocumentString)
// if you want to validate your document to verify it matches your schema
const errors = validate(schema, document)

AFAIK, there's no utility function for getting an array of the types in a document, if that's what you're asking for, but you can just traverse the AST and gather whatever information from it. As an example, here's how GraphiQL does just that to generate a map of variables to their corresponding types:

import { typeFromAST } from 'graphql'

export function collectVariables(schema, documentAST) {
  const variableToType = Object.create(null);
  documentAST.definitions.forEach(definition => {
    if (definition.kind === 'OperationDefinition') {
      const variableDefinitions = definition.variableDefinitions;
      if (variableDefinitions) {
        variableDefinitions.forEach(({ variable, type }) => {
          const inputType = typeFromAST(schema, type);
          if (inputType) {
            variableToType[variable.name.value] = inputType;
          }
        });
      }
    }
  });
  return variableToType;
}