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Model Data - React Native SDK

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  • Realm Schema
  • Relationships

Every Realm object conforms to a specific object type. Object types are classes you define that contain 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 React Native 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.

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.

Using @realm/react, you define a realm schema by passing individual object schemas to RealmProvider or createRealmContext().

import Profile from './Models/Profile';
import {createRealmContext} from '@realm/react';
export const SyncedRealmContext = createRealmContext({
// Pass all of your models into the schema value.
schema: [Profile],

You can define relationships between objects in a realm. Realm models relationships as object properties that point to other objects of a given type in the realm. You define a relationship at the type level by declaring a property in the type's schema where the value is another object type.

Querying a relationship is just as performant as a regular property. Relationships are direct references to other objects, so you don't need to use joins and complex models to define and use them like you would in a relational database. Instead, you can access related objects by reading and writing to the relationship property directly.

There are three primary types of relationships between objects:


Realm vs Other Databases

Objects often contain direct references to other objects. When working with objects and references, you typically copy data from database storage into application memory. This situation leaves the developer with a choice of what to copy into memory:

  • You can copy all referenced objects into memory ahead of time. This means that all referenced data is always available quickly but can use up a lot of resources. If a system has limited memory, this may not be viable.

  • You can copy just a foreign key value for each object. Later, you can use the key to look up the full object when you need it. These "lazy" lookups are more memory-efficient than copying all referenced objects ahead of time. However, they require you to maintain more query code and use runtime lookups that can slow your app down.

Realm's query architecture avoids the tradeoff between memory usage and computational overhead. Instead, Realm queries can directly reference related objects and their properties on disk.


See also:

Alternatively, you can define your relationships in your App Services app.

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