javascript - 我正在尝试使用 JavaScript 将海报 URL 添加到我的 neo4j 电影数据库，但我总是收到此 undefined object 错误

Question

我对 JavaScript 完全陌生，很难理解异步调用。我是否需要嵌套另一个 Promise 对象来设置海报 URL？

async function getIds() {
    const result = await session.run("MATCH (m :Movie) RETURN m.imdbId LIMIT 5");
    const ids = [];
    result.records.forEach(record => ids.push(record._fields[0]));
    return ids;
}

async function imdbIds() {
    const ids = await getIds();
    console.log(ids);
    const response = await Promise.all(ids.map(async id => {
        // webscraper that returns poster url of each imdbid
        const url = toString(scraper(id));
        console.log(url);

        // query to set poster of each id in neo4j db
        const result = await session.run("MATCH (m :Movie {imdbId : $id}) SET m.poster = $url RETURN m.poster", { id, url });
        result.records.forEach(record => console.log(record._fields[0]));
        return result;
    }));
    console.log(response);
}

imdbIds();

控制台日志仍然没有运气:

[ '0114709', '0113497', '0113228', '0114885', '0113041' ]
[object Undefined]
[object Undefined]
[object Undefined]
[object Undefined]
[object Undefined]
[object Undefined]
[object Undefined]
[object Undefined]
[object Undefined]
[object Undefined]
[ { records: [ [Record] ],
    summary:
     ResultSummary {
       statement: [Object],
       statementType: 'rw',
       counters: [StatementStatistics],
       updateStatistics: [StatementStatistics],
       plan: false,
       profile: false,
       notifications: [],
       server: [ServerInfo],
       resultConsumedAfter: [Integer],
       resultAvailableAfter: [Integer] } } ...

Answer 1

问题出在您的 getIds 函数上。你已经将一个已经 promise 返回的函数包装在另一个 promise 中。第二个问题是你的 getIds 函数。您正在 forEach 中执行异步操作，这是行不通的。将其替换为 Promise.all 它应该是这样的

async function getIds() {
  const result = await session.run("MATCH (m :Movie) RETURN m.imdbId LIMIT 5");
  const ids = [];
  result.records.forEach(record => ids.push(record._fields[0]));
  return ids;
}

async function imdbIds() {
  const ids = await getIds();
  console.log(ids);
  const response = await Promise.all(ids.map(async id => {
    // webscraper that returns poster url of each imdbid
    const url = toString(scraper(id));
    console.log(url);

    // query to set poster of each id in neo4j db
    const result = await session.run("MATCH (m :Movie {imdbId : $id}) SET m.poster = $url RETURN m.poster", {id, url});
    result.records.forEach(record => console.log(record._fields[0]));
    return result;
  }));
  console.log(response);
}