javascript - 如何使用 Promise 异步调用此函数

Question

我正在尝试创建一个 parse.com 函数，该函数检查数据库中的记录并创建新记录或返回现有记录(如果存在)。我想异步执行此操作，并且我正在尝试使用 Promise(我想是 q )。语法让我有点困惑，这是我尝试过的，但它抛出错误“无法调用未定义的方法‘then’”我该如何将其写为正确的 promise 。

  function createPersonIfDoesNotExist(personName)
  {
    var Person = Parse.Object.extend("Person");
    var personQuery = new Parse.Query(Person);
    personQuery.equalTo("Name", personName);
    personQuery.find({
      success: function(results) {
        console.log("Successfully retrieved " + results.length + " person.");
        if(results.length >0){
          console.log("Looks like this person exists already, no point it making a new one");
          var artist =  results[0];
          return artist;
        }
        else
        {
          // Create a new Person
          var person = new Person();
          return person;
        }
      },
      error: function(error) {
        console.log("Error: " + error.code + " " + error.message);
        return error;
      }
    });
  }

  var promise = createPersonIfDoesNotExist(personname);
  promise.then(console.log, console.error);

Answer 1

OP 代码不返回任何内容。它应该返回的是由 parse find() 或 save() 方法生成的 Promise。

如果您编写小函数，在解析 promise 返回函数上创建小的增值 promise ，那么阅读和维护会变得更容易...

// return a promise that is fulfilled with a new Person with the given name
function createPersonNamed(personName) {
    var Person = Parse.Object.extend("Person");
    var person = new Person();
    person.set("Name", personName);
    return person.save();
}

// return a promise that is fulfilled with the first existing person with a given name
function findPersonNamed(personName) {
    var Person = Parse.Object.extend("Person");
    var personQuery = new Parse.Query(Person);
    personQuery.equalTo("Name", personName);
    return personQuery.first();
}

// return a promise that is fulfilled with either an existing person with a given name,
// or a newly created one if the Person does not exist
function findOrCreatePersonNamed(personName) {
    return findPersonNamed(personName).then(function(person) {
        return (person)? person : createPersonNamed(personName);
    });
}