Apollo GraphQL解析器报错：Cannot read properties of undefined (reading 'liked')

在Sandbox中执行带过滤的GraphQL查询时，收到以下错误：

"TypeError: Cannot read properties of undefined (reading 'liked')",
" at Object.movies (.../server/schema/resolvers.js:14:45)"

我尝试修改类型定义和查询来测试其他属性，但错误依旧。相关代码如下：

相关代码 #

index.js #

const { ApolloServer } = require("apollo-server");
const { typeDefs } = require("./schema/type-defs");
const { resolvers } = require("./schema/resolvers");

const server = new ApolloServer({ typeDefs, resolvers });

server.listen().then(({ url }) => {
  console.log(`YOUR API IS RUNNING AT: ${url} :)`);
});

FakeData.js #

const MovieList = [
  {
    id: 1,
    name: "Avengers Endgame",
    year: 2019,
    liked: true,
  },
  {
    id: 2,
    name: "Interstellar",
    year: 2007,
    liked: true,
  },
  {
    id: 3,
    name: "Superbad",
    year: 2007,
    liked: true,
  },
  {
    id: 4,
    name: "Madagascar 12",
    year: 2073,
    liked: false,
  },
];

module.exports = { MovieList };

type-defs.js #

const { gql } = require("apollo-server");

const typeDefs = gql`
  type Movie {
    id: ID!
    name: String!
    year: Int!
    liked: Boolean!
  }

  input MovieFilters {
    liked: Boolean!
    year: Int!
  }

  input MovieInput {
    filter: MovieFilters
  }

  type Query {
    movie(id: ID!): Movie
    movies(input: MovieInput): [Movie]!
  }
`;

module.exports = { typeDefs };

resolvers.js #

const { MovieList } = require("../FakeData");
const _ = require("lodash");

const resolvers = {
  Query: {
    movies: (parent, args) => {
      const { filter } = args;
      const shouldApplyFilters = filter !== null;

      let movies = MovieList;

      if (!shouldApplyFilters) return movies;

      const shouldApplyLikedFilter = filter.liked !== null;
      const shouldApplyYearFilter = filter.year !== null;

      if (shouldApplyLikedFilter) {
        movies = movies
          .filter((a) => a.liked === filter.liked)
      }

      if (shouldApplyYearFilter) {
        movies = movies
          .filter((a) => a.year === filter.year)
      }

      return movies;
    },
  }
};

module.exports = { resolvers };

查询语句 #

query GetMoviesByFilter($input: MovieInput) {
  movies(input: $input) {
    id
    name
    liked
    year
  }
}

查询变量 #

{
  "input": {
    "filter": {
      "year": 2007,
      "liked": true
    }
  }
}

问题原因与修复 #

核心错误 #

resolvers.js 中参数解构错误：你直接从 args 中解构 filter，但实际传入的参数是包裹在 input 对象里的，导致 filter 为 undefined，后续读取 filter.liked 就会报错。

修复后的代码 #

修复 resolvers.js

const { MovieList } = require("../FakeData");

const resolvers = {
  Query: {
    movies: (parent, args) => {
      // 正确从input中提取filter
      const { input } = args;
      const filter = input?.filter;

      let movies = [...MovieList]; // 拷贝原数组避免修改源数据

      if (!filter) return movies;

      // 同时处理undefined和null的情况
      if (filter.liked !== undefined && filter.liked !== null) {
        movies = movies.filter(a => a.liked === filter.liked);
      }

      if (filter.year !== undefined && filter.year !== null) {
        movies = movies.filter(a => a.year === filter.year);
      }

      return movies;
    },
  }
};

module.exports = { resolvers };

优化 type-defs.js（可选）

原 MovieFilters 中 liked 和 year 设为必填，实际场景中可能只需要单个过滤条件，建议改为可选：

const { gql } = require("apollo-server");

const typeDefs = gql`
  type Movie {
    id: ID!
    name: String!
    year: Int!
    liked: Boolean!
  }

  input MovieFilters {
    liked: Boolean
    year: Int
  }

  input MovieInput {
    filter: MovieFilters
  }

  type Query {
    movie(id: ID!): Movie
    movies(input: MovieInput): [Movie]!
  }
`;

module.exports = { typeDefs };

内容的提问来源于stack exchange，提问作者paq