Question

我正在使用loopback 3来构建REST服务，我想使用async / await而不是必须使用回调。所以不要这样做：

MyModel.myFunction = (callback) => {
  MyModel.find({where: {id: 2}}, (e, data) => {
    if (e) return callback(e);
    callback(null, data);
  });
};

我更愿意这样做：

MyModel.myFunction = async (callback) => {
  try {
    const data = await MyModel.find({where: {id: 2}});
    callback(null, data);
  } catch (e) {
    console.error(e);
    callback(e);
  }
};

回调方法完美无缺 - async / await会产生很多错误：

UnhandledPromiseRejectionWarning: Error: Callback was already called.
UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch().

怎么了？我无法解决这个问题。

Answer 1

一些重构：

MyModel.myFunction = async () => {
  try {
    const data = await MyModel.find({where: {id: 2}});
    return data; // it's enough as the async means it returns a promise
  } catch (e) {
    console.error(e);
    throw e;
  }
};

如果您不需要记录错误（环回错误处理程序将其记录而不是您），则会出现此情况：

MyModel.myFunction = async () => {
  return MyModel.find({where: {id: 2}});
};

Answer 2

看起来我只是混合了两个概念，这就是解决方案：

MyModel.myFunction = async (callback) => {
  try {
    const data = await MyModel.find({where: {id: 2}});
    return Promise.resolve(data);
  } catch (e) {
    console.error(e);
    return Promise.reject(e);
  }
};

Answer 3

一种更简单的方法是只使用一个函数来解决您的诺言，然后将db查询传递给它，就像这样。

async function ReturnWithResolvedPromise(dbQuery) {
try {
    return Promise.resolve(dbQuery);
} catch (e) {
    return Promise.reject(e);
}}

然后这样称呼

let result =    await ReturnWithResolvedPromise(await Users.count({where: {Region: 'UK'}}));

对async / await的环回支持

3 个答案: