React Native MongoDB Realm - How to create a object in a One-to-Many Relationship?

Question

I am working on React Native MongoDB Realm database.

The doc explains how to create a One-to-Many Relationship schema as shown below:

const Person = {
  name: "Person",
  properties: {
    name: "string",
    birthdate: "date",
    dogs: "Dog[]"
  }
};

const Dog = {
  name: "Dog",
  properties: {
    name: "string",
    age: "int",
    breed: "string?"
  }
};

But I dont see where it explains how to add in the database Dog objects that belong to a person. A Person should be specified in some way.

I am using Realm React, so the dog creation code looks something like :

person1: Person =  ...

realm.write(() => {
   return  new Dog(realm, dogFields);
});

If I have a person1 already in the DB, how to modify this code so that person1 becomes the owner of this newly created dog.

Answer 1

A good conceptual question and I think this can be addressed at a high level.

Start with some pseudo code for a Person Object with a name and a list of dogs and a Dog object.

Person {
  name = ""
  dogs = List of dogs
}

Dog {
  name = ""
}

Conceptually, if a Person is instantiated in code

let p = Person()

and then a dog

let d = Dog()

and then the dog is added to the Persons dogs property,

p.dogs.add(d)

when the Person is written to Realm within a write transaction, the dogs will be too! How cool is that?

realm.write {
   realm.add(p) //the person and its dog is added; both objects are written
}

Another example is if there’s in existing person that’s already been written. When it’s read in and new dogs are added to the person (within a write transaction), they will be added to the persons list and also be written as separate objects

Lastly, if there are Person and Dogs that have already been written, if a person is read in, and then a dog is read in, when the dog is added the Person Dog property within a write transaction, it will just update the person since the dog already exists.