parse.com many-to-many get list of Pointer ID with Javascript

Question

I have a problem with a many-to-many relationship on parse.com.

First of all I have two classes (Groups and Users) and a class (UserInGroup) to realize the m-to-m relationship.

Class structure:

Groups: objectId(string) -- GroupName(string) -- ...

Users: objectId(string) -- UserName(string) -- ...

UserInGroup: objectId(string) -- Group(Pointer< Groups>) -- User(Pointer< Users>)

How can I get the UserName of alle Users who are in a specificGroup (I know the objectId of the Group).

I trieds this

function getUserNameOfGroup(GroupID){
    var UserInGroup = Parse.Object.extend("UserInGroup");
    var query = new Parse.Query(UserInGroup);
    var usersArray = [];

    var Groups = Parse.Object.extend("Groups");
    var collectionQuery = new Parse.Query(Groups);
    collectionQuery.get(GroupID, {
        success: function(group) {
            query.equalTo("Group", group);
            var usersArray = [];
            query.find({
                success: function(results) {
                    for (var i = 0; i < results.length; i++) { 
                        var object = results[i];

                        var user = object.get("User");
                        user.fetch({
                          success: function(tempUser) {
                                usersArray.push(user.get("UserName"));
                          }
                        }).done(function() {
                            if(results.length == usersArray.length){

                                //do something with the array
                            }
                        });
                    }
                },
                error: function(error) {
                    alert("Error: " + error.code + " " + error.message);
                }
            });
        },
        error: function(object, error) {
            alert("Error: " + error.code + " " + error.message);
        }
    });
}

For testing I put

if(results.length == usersArray.length){
    for (var i = 0; i < usersArray.length; i++) { 
        alert(usersArray[i]);
    }
}

in the done section. The first entry of usersArray is always "undefinde".

What am I doing wrong? Or rather, is there an easier, more beautiful and faster way to get the array? I'm sure there's a better solution ;).

thanks for help.

danh · Accepted Answer · 2015-05-12 17:45:09Z

1

No need to do an additional query on the UserInGroup's User attribute. Those can be fetched eagerly using include(), as follows:

// return a promise that is fulfilled with an array of users belonging to
// the Group with id groupId
function usersInGroup(groupId) {
    var groupQuery = new Parse.Query("Groups");
    return groupQuery.get(groupId).then(function(group) {
        var userInGroupQuery = new Parse.Query("UserInGroup");
        userInGroupQuery.equalTo("Group", group);
        // eagerly fetch the related user...
        userInGroupQuery.include("User");
        return userInGroupQuery.find();
    }).then(function(results) {
        var users = [];
        for (var i = 0; i < results.length; i++) { 
            var object = results[i];
            users.push(object.get("User"));
        }
        return users;
    });
}

Call it like this:

usersInGroup(someGroupId).then(function(users) {
    for (var i = 0; i < users.length; i++) { 
        var user = users[i];
        console.log(user.getUserName());  // or get("username")
    }
}, function(error) {
    console.log(error);
});

edited May 12, 2015 at 17:45

answered May 12, 2015 at 16:58

danh

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2 Comments

Mr.P. Over a year ago

thank you it works after correcting an error at the call

danh Over a year ago

Glad to help. Sorry about the copy paste error on the loop. Will fix. But I think getUsername() is the correct method to get a user's username. Either that or .get("username") works with all lowercase.

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