emilbonnek / rust-playground

Problem:

I have a Parent and a Child that has references to each other like so:

struct Parent {
    id: u64,
    child: Rc<RefCell<Child>>,
}
struct Child {
    id: u64,
    parent: Weak<RefCell<Parent>>,
}

I am trying to set up Deserialization for the Parent with serde. The JSON representation should be like so:

{
    "id": 1,
    "child": {
        "id": 100,
        "parent_id": 1,
    }
}

However I can't seem to figure out how to actually do this. The problem I face in the end is that I no longer have ownership of the Parent because I need to pass it to the Rc<RefCell>.

Details

Since I need to deserialize in such a way that the parent_id field becomes a parent refering to the actual Parent I start by having an intermediate struct called ChildDTO that can easily deserialize.

#[derive(Deserialize)]
pub struct ChildDTO {
    pub id: u64,
    pub parent_id: u64,
}

Next I can implement Deserialization for the Parent. However at the last step of the deserialization when I have to set up the references I am forced to give up ownership of the parent and so I can't return a Parent.

// (child is a a ChildDTO at this point)
if child.parent_id != id {
    return Err(de::Error::custom("Parent id and child parent_id mismatch"));
}

let child = Rc::new(RefCell::new(Child {
    id: child.id,
    parent: Weak::new(),
}));
let parent = Rc::new(RefCell::new(Parent { id, child }));

// Setting the parent weak reference
parent.borrow().child.borrow_mut().parent = Rc::downgrade(&parent);

Ok(parent) // I want to return a Parent, but now I am stuck returning an Rc<RefCell<Parent>>