解析云代码检索具有 objectId 的用户

Question

我正在尝试从 objectId 获取用户对象。我知道 objectId 是有效的。但我可以让这个简单的查询工作。它有什么问题？查询后用户仍未定义。

var getUserObject = function(userId){
    Parse.Cloud.useMasterKey();
    var user;
    var userQuery = new Parse.Query(Parse.User);
    userQuery.equalTo("objectId", userId);

    userQuery.first({
        success: function(userRetrieved){
            console.log('UserRetrieved is :' + userRetrieved.get("firstName"));
            user = userRetrieved;               
        }
    });
    console.log('\nUser is: '+ user+'\n');
    return user;
};

Answer 1

使用 Promise 的快速云代码示例。我有一些文档，希望你能关注。如果您需要更多帮助，请告诉我。

Parse.Cloud.define("getUserId", function(request, response) 
{
    //Example where an objectId is passed to a cloud function.
    var id = request.params.objectId;

    //When getUser(id) is called a promise is returned. Notice the .then this means that once the promise is fulfilled it will continue. See getUser() function below.
    getUser(id).then
    (   
        //When the promise is fulfilled function(user) fires, and now we have our USER!
        function(user)
        {
            response.success(user);
        }
        ,
        function(error)
        {
            response.error(error);
        }
    );

});

function getUser(userId)
{
    Parse.Cloud.useMasterKey();
    var userQuery = new Parse.Query(Parse.User);
    userQuery.equalTo("objectId", userId);

    //Here you aren't directly returning a user, but you are returning a function that will sometime in the future return a user. This is considered a promise.
    return userQuery.first
    ({
        success: function(userRetrieved)
        {
            //When the success method fires and you return userRetrieved you fulfill the above promise, and the userRetrieved continues up the chain.
            return userRetrieved;
        },
        error: function(error)
        {
            return error;
        }
    });
};

Answer 2

问题在于 Parse 查询是异步的。这意味着它将在查询有时间执行之前返回 user (null)。无论您想对用户做什么，都需要放在成功中。希望我的解释可以帮助您理解为什么它是未定义的。

查看Promises。在您从第一个查询中获得结果后，这是一种更好的调用方式。