解决Graphql的异步函数无法返回在具有rdf数据的Stardog服务器上查询的数据

Question

我试图使用graphql查询stardog服务器是我的代码。

import {
  GraphQLSchema,
  GraphQLObjectType,
  GraphQLInt,
  GraphQLString,
  GraphQLList,
  GraphQLNonNull,
  GraphQLID,
  GraphQLFloat
} from 'graphql';

import axios from 'axios';

var stardog = require("stardog");

let Noun = new GraphQLObjectType({
      name: "Noun",
      description: "Basic information on a GitHub user",
      fields: () => ({
          "c": {
       type: GraphQLString,
       resolve: (obj) => {
        console.log(obj);
          }
        }
     })
});

const query = new GraphQLObjectType({
      name: "Query",
      description: "First GraphQL for Sparql Endpoint Adaptive!",
      fields: () => ({
        noun: {
          type: Noun,
          description: "Noun data from fibosearch",
          args: {
            noun_value: {
              type: new GraphQLNonNull(GraphQLString),
              description: "The GitHub user login you want information on",
            },
          },
          resolve: (_,{noun_value}) => {
              var conn = new stardog.Connection();

              conn.setEndpoint("http://stardog.edmcouncil.org");
              conn.setCredentials("xxxx", "xxxx");
                conn.query({
                    database: "jenkins-stardog-load-fibo-30",
                    query: `select ?c  where {?s rdfs:label '${noun_value}'. ?c rdfs:subClassOf ?s}`,  
                    limit: 10,
                    offset: 0
                },
                function (data) {
                       console.log(data.results.bindings);
                       return data.results.bindings;
                });  
              }
            },
          })
      });

const schema = new GraphQLSchema({
  query
});

export default schema;

查询执行成功，我能够在控制台上看到结果，但return data.results.bindings;中的function(data)没有将此结果返回到Noun下的resolve: (obj) => { console.log(obj); }类型系统，并且返回的obj显示为null而不是从GraphQL查询返回的结果bindings。如果有人能帮助我弄清楚我在这里缺少什么，那就太好了。

提前谢谢，Yashpal

Answer 1

在您的查询中，resolve字段的noun函数是一个异步操作（查询部分）。但是你的代码是同步的。因此，实际上不会立即从resolve函数返回任何内容。这导致没有传递给Noun GraphQL对象类型的resolve函数。这就是为什么当你打印obj时你得到null。

如果在resolve函数中进行异步操作，则必须返回一个与您的预期结果一起解析的promise对象。您还可以使用ES7 async / await功能;在这种情况下，你必须申报resolve: async (_, {noun_value}) => { // awaited code}。

使用Promise，代码如下所示：

resolve: (_,{noun_value}) => {
  var conn = new stardog.Connection();

  conn.setEndpoint("http://stardog.edmcouncil.org");
  conn.setCredentials("xxxx", "xxxx");
  return new Promise(function(resolve, reject) {
    conn.query({
      database: "jenkins-stardog-load-fibo-30",
      query: `select ?c  where {?s rdfs:label '${noun_value}'. ?c rdfs:subClassOf ?s}`,  
      limit: 10,
      offset: 0
    }, function (data) {
      console.log(data.results.bindings);
      if (data.results.bindings) {
        return resolve(data.results.bindings);
      } else {
        return reject('Null found for data.results.bindings');
      }
    });
  });
}