javascript - 如何从 Sails.js 中的此方法返回 n 的值

Question

getCount: (filter = null) => {
  var whereConditions = {};
  if(filter != null) whereConditions.role = filter;

  User
    .count({
      where: whereConditions,
    })
    .exec((err, n) => {
      console.log(n);
      return n;
    });
}

上面的方法在调用时返回undefined，但是当我console.log n时，我得到了正确的输出。我该如何解决这个问题？

Answer 1

where()应该返回 promise这意味着您可以使用 then()和catch()在代码中调用getCount(filter)您的“服务”，以根据需要访问值和错误的成功响应。根据documentation , .exec()可以直接替换为then()和catch() 。尝试如下操作:

服务:

getCount: (filter = null) => {
  var whereConditions = {};
  if(filter != null) whereConditions.role = filter;

  // return promise
  // using this value directly will not allow you to access queried values
  return User.count({ where: whereConditions });
}

Controller /调用者:

this.someService.getCount('someFilterValue')
  .then(values = {
      console.log(values);
      // do something with values like bind to variable/property of the view
  })
  .catch(error => console.log(error));

或者根据您的结构，您可以尝试类似的方法来完成 getCount() 内的所有操作:

getCount: (filter = null) => {
  var whereConditions = {};
  if(filter != null) whereConditions.role = filter;

  // return promise
  // using this value directly will not allow you to access queried values
  return User
      .count({ where: whereConditions })
      .then(values => res.json(values))
      .catch(error => res.serverError(error));
}

您可以委托(delegate) then() 中的功能的getCount()到一个单独的方法来减少重复:

 getCount: (filter = null) => {
  var whereConditions = {};
  if(filter != null) whereConditions.role = filter;

  // return promise
  // using this value directly will not allow you to access queried values
  return User
      .count({ where: whereConditions })
      .then(handleResponse)
      .catch(error => res.serverError(error));
},

handleResponse: (data) => {
  // do something with data
  return data.map(e => e.someProperty.toUpperCase());
}

您可以链接then()每次返回转换后的值时，根据需要继续转换值。只要继续返回值，您就可以将其委托(delegate)给方法。这还允许您采取异步操作，并且仅在解决它们后才对其进行操作。

getCount: (filter = null) => {
  var whereConditions = {};
  if(filter != null) whereConditions.role = filter;

  // return promise
  // using this value directly will not allow you to access queried values
  return User
      .count({ where: whereConditions })
      .then(values => values.map(e => e.someProperty.toUpperCase()))
      .then(transformedValues => transformedValues.filter(e => e.indexOf(filter) > -1))
      .then(filteredValues => res.json(filteredValues))
      .catch(error => res.serverError(error));
}

希望有帮助!