Android : Get objects from multiple Relations

Question

Say, I have a Food class, in which I have 3 relations - 'Lovers', 'Eaters', 'Makers'. I added users to each of these relations.

Now I want to display for a particular food, a list which shows all 'Lovers' first, then 'Makers', and all 'Eaters' at the end - in this order.

So to retrieve only Lovers, I have to do ParseQuery on Lovers, and then find(), from which I store the list of users in an ArrayList. Then again I repeat the same procedure for Makers and Eaters and append the result to my ArrayList.

This process is slow, tedious and resource consuming. Is there a better way ?

EDIT

Food class(ParseObject) is as follows

• Lovers - Relation<_User>
• Eaters - Relation<_User>
• Makers - Relation<_User>
• --- and other variables like cuisine, country, etc ---

User class(ParseUser) is as follows ##

• name
• age

Every food makes a 'Lovers' relation with users who love the food, same for 'Eaters' and 'Makers'

To get Lovers, then Makers and then Eaters for a 'food' object, I use following query

ArrayList<User> userList = new ArrayList<User>();

ParseRelation<ParseObject> relation = food.getRelation("Lovers");
ArrayList<User> lovers =relation.getQuery().find();

ParseRelation<ParseObject> relation = food.getRelation("Makers");
ArrayList<User> makers =relation.getQuery().find();

ParseRelation<ParseObject> relation = food.getRelation("Eaters");
ArrayList<User> eaters =relation.getQuery().find();

userList.add(lovers);
userList.add(makers);
userList.add(eaters);

Unfortunately Parse does not support 'include' in query on relations and I dont want to use Array to store the relationship (coz in future I may need to find what a user loves, eats and makes). So, is there a solution get these 3 relations data in single query.

Answer 1

Yes, you can query all 3 classes using 1 class. I would create a relationships class, which has pointers to each of the 3 classes you want to query, and then directly query this relationships class to include the pointers to the 3 classes. Then you can just create objects of the 3 classes and use them.

Answer 2

One option would be to create a class to be your join table, as is done in some of the samples provided on Parse.

UserFood:
User: link to User class
Food: link to Food class
MakesIt: bool
LovesIt: bool
EatsIt: bool

Getting all users for a food becomes a simple query, getting all foods for a user becomes simple. If you just want a list of 'Lovers' you can filter on the 'LovesIt' = true.

It also makes it easy to do a query like: find my all foods where the person that makes it also eats it.

Answer 3

Yes and no. If you are retrieving from separate classes, you need to do 3 separate callbacks. But depending on how your structured and what your really trying to accomplish, you could look into Relational queries

Answer 4

you can add as a relation your custom class instead of _User

In your custom class you can store a user as a one field and his status (lover, eater, maker) on the other so you can query for all users at once