How to get parent object from relation in Parse

Question

Let's say I have a class Parent that has a one-to-many relation with a target class Child. Both Parent and Child objects are not user created, I am creating this objects in Data Browser and I don't know how to set a relationship or a pointer on a Child back to it's particular Parent. I can get Child objects of a Parent with no problem. But, how can I get the Parent of a Child? I don't want to keep passing both Parent and Child objects from VC to VC. Once again both objects are NOT user created so I can't do:

[Parent setObject:Child forKey:"child"];

and then query Parent class like this:

[query whereKey:@"child" isEqualTo:Child];

Also querying all Parents and their relations and then getting that particular Child and then going back to the Parent seem to be an overkill.

So, how can I set the particular Parent on a Child object in Data Browser to point back to the parent? And how to get that Parent object from the code if I want to use only Child object?

Answer 1

This is a case of where using a reverse pointer might be more useful. This can be done in addition to your existing relationship if you want, but requires some fancier save logic.

Simply add a parent column to Child that is of type Pointer<Parent> .

To get all children of a parent you just do a query:

[childQuery whereKey:@"parent" isEqualTo:parent];

To query a child and also get the parent:

[childQuery includeKey:@"parent"];
// filter as needed

In the block that looks are children you can just use:

PFObject *parent = child[@"parent"];

It will be a fully populated Parent due to the includeKey: .

NOTE: if you keep both relationships, creating new objects gets trickier as you'll have to save the parent/child (with child.parent unset) then update the child to point to the parent and save it again.