Model Data - Node.js SDK

Object Types & Schemas

Every Realm object conforms to a specific object type, which is essentially a class that defines the properties and relationships for objects of that type using a pre-defined schema. Realm guarantees that all objects in a realm conform to the schema for their object type and validates objects whenever they're created, modified, or deleted.

Realm objects are fundamentally similar to a common JavaScript object but they also bring along a few additional features like schema validation and live queries. The Node.js SDK memory maps Realm objects directly to native JavaScript objects, which means there's no need to use a special data access library, such as an ORM. Instead, you can work with Realm objects as you would any other object.

The following class contains a schema that defines a Car object type with id, make, model, and miles properties. It also defines a primary key.

class Car extends Realm.Object {
  static schema = {
    name: "Car",
    properties: {
      _id: { type: "objectId", default: () => new Realm.BSON.ObjectId() },
      make: "string",
      model: "string",
      miles: "int?",
    },
    primaryKey: "_id",
  };
}

Realm Schema

A realm schema is a list of valid object schemas that a realm may contain. Every Realm object must conform to an object type that's included in its realm's schema.

If a realm already contains data when you open it, Realm validates each object to ensure that an object schema was provided for its type and that it meets all of the constraints specified in the schema.

A realm that contains basic data about cars and manufacturers might use a schema like the following:

class Manufacturer extends Realm.Object {
  static schema = {
    name: "Manufacturer",
    properties: {
      _id: "objectId",
      // A manufacturer that may have many cars
      cars: "Car[]",
    },
  };
}
class Car extends Realm.Object {
  static schema = {
    name: "Car",
    properties: {
      _id: "objectId",
      make: "string",
      model: "string",
      miles: "int?",
    },
  };
}

Relationships

Realm allows you to define explicit relationships between the types of objects in an App. A relationship is an object property that references another Realm object type. You can define relationships by setting an object's property to another object type in the property schema.

Relationships are direct references to other objects in a realm. You don't need bridge tables or create joins to define a relationship like you would in a relational database. Instead you can access related objects by reading and writing to the property that defines the relationship.

Realm executes read operations lazily as they come in. Querying a relationship is just as performant as reading a regular property.

There are three primary types of relationships between objects:

• One-to-One Relationship

• One-to-Many Relationship

• Inverse Relationship