解析云代码：承诺中的逻辑分支

Question

I'm trying to write a Parse.com Cloud Code function to accomplish the following workflow:

1. User submits a value.
2. Cloud code function checks to see if that value matches any objects of type code .
3. If not, the function returns a "not found" value.
4. If so, the object of type code is assumed to have a pointer to an object of type item .
5. Then, code.item is checked to see whether it has a pointer to an object of type alert .
6. If not, the function returns a "not found" value.
7. If code.item.alert does exist, then I want to fetch the full alert object, including pointers which may or may not exist, up to 2 layers deep.

As I begin writing the code for this function, I can get it working to the point of checking to see whether the code exists and, if so, whether code.item.alert also exists.

This is where the problem arises. As it currently stands, in the working version of my function, the alert item that is returned is only the class type and objectId. I understand why that is happening, and I am trying to write code to populate the object before returning it, but I am failing in that attempt.

Here's the code that is working so far (but only returning the alert object's shell):

Parse.Cloud.define("alertLookup", function (request, response) {
    Parse.Cloud.useMasterKey(); 

    var codeQuery       = new Parse.Query("code");  
    codeQuery.equalTo("value", request.params.code);
    codeQuery.include("item");

    codeQuery.find().then(function (codes) {
        if (codes.length === 0) {
            response.success("no item");
        } else {
            var code    = codes[0];
            var item    = code.get("item");
            var alert   = item.get("alert");
            if (alert === null || alert === undefined) {
                response.success("no item");
            } else {
                response.success(alert);
            }
        }       
    }, function (error) {
        response.error(error);
    });
});

Here's what I have tried that is failing with an error code of 141:

Parse.Cloud.define("alertLookup", function (request, response) {
    Parse.Cloud.useMasterKey(); 

    var codeQuery       = new Parse.Query("code");  
    codeQuery.equalTo("value", request.params.code);
    codeQuery.include("item");

    codeQuery.find().then(function (codes) {
        if (codes.length === 0) {
            response.success("no item");
        } else {
            var code    = codes[0];
            var item    = code.get("item");
            var alert   = item.get("alert");
            if (alert === null || alert === undefined) {
                response.success("no item");
            } else {
                return alert.fetch();                   
            }
        }       
    }).then(function (a) {
        response.success(a);

    }, function (error) {
        response.error(error);
    });
});

Why won't the fetch() call work properly? When I insert console.log() statements, although alert is non-null, return alert.fetch(); does not ever seem to be called. At least, the response.success(a); line is never called. Why not?

Answer 1

Try this instead while chaining Promises:

codeQuery.find().then(function (codes) {
    if (codes.length != 0) {
        var code    = codes[0];
        var item    = code.get("item");
        var alert   = item.get("alert");
        if (alert != null && alert != undefined) {
            var alertObj = new Parse.Object("alert"); // alert class ???
            alertObj.id = alert.id;
            return alertObj.fetch();                   
        }
    }
    // return a Promise for no items
    return Parse.Promise.as("no item");

}).then(function (a) {
    response.success(a);

}, function (error) {
    response.error(error);
});