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Embedded Objects - React Native SDK

An embedded object is a special type of Realm object that models complex data about a specific object. Embedded objects are similar to relationships, but they provide additional constraints and map more naturally to the denormalized MongoDB document model.

Realm enforces unique ownership constraints that treat each embedded object as nested data inside a single, specific parent object. An embedded object inherits the lifecycle of its parent object and cannot exist as an independent Realm object. This means that embedded objects cannot have a primary key and that Realm automatically deletes embedded objects if their parent object is deleted.

Tip
Embedded object types are reusable and composable

You can use the same embedded object type in multiple parent object types, and you can embed objects inside other embedded objects. You can even recursively reference an embedded object type as an optional property in its own definition.

Note
Realm Uses Cascading Deletes for Embedded Objects

When you delete a Realm object, Realm automatically deletes any embedded objects referenced by that object. Any objects that your application must persist after the deletion of their parent object should use relationships instead.

To define an embedded object, set embedded to true. You can reference an embedded object type from parent object types in the same way as you would define a relationship:

Important

Embedded objects cannot have a primary key.

const AddressSchema = {
name: "Address",
embedded: true, // default: false
properties: {
street: "string?",
city: "string?",
country: "string?",
postalCode: "string?",
},
};
const ContactSchema = {
name: "Contact",
primaryKey: "_id",
properties: {
_id: "objectId",
name: "string",
address: "Address", // Embed a single object
},
};
const BusinessSchema = {
name: "Business",
primaryKey: "_id",
properties: {
_id: "objectId",
name: "string",
addresses: { type: "list", objectType: "Address" }, // Embed an array of objects
},
};

Unlike regular Realm objects, which map to their own MongoDB collection, embedded objects map to embedded documents in the parent type's document schema:

{
"title": "Contact",
"bsonType": "object",
"required": ["_id"],
"properties": {
"_id": { "bsonType": "objectId" },
"name": { "bsonType": "string" },
"address": {
"title": "Address",
"bsonType": "object",
"properties": {
"street": { "bsonType": "string" },
"city": { "bsonType": "string" },
"country": { "bsonType": "string" },
"postalCode": { "bsonType": "string" }
}
}
}
}
{
"title": "Business",
"bsonType": "object",
"required": ["_id", "name", "addresses"],
"properties": {
"_id": "objectId",
"name": { "bsonType": "string" },
"addresses": {
"bsonType": "array",
"items": {
"title": "Address",
"bsonType": "object",
"properties": {
"street": { "bsonType": "string" },
"city": { "bsonType": "string" },
"country": { "bsonType": "string" },
"postalCode": { "bsonType": "string" }
}
}
}
}
}

To create an embedded object, assign an instance of the embedded object to a parent object's property:

// create an embedded address object
const sydneyOrthodontics = {
street: "42 Wallaby Way",
city: "Sydney",
country: "Australia",
postalCode: "2774",
};
realm.write(() => {
// create a contact object
realm.create("Contact", {
_id: new BSON.ObjectId(),
name: "Philip Sherman",
address: sydneyOrthodontics, // embed the address in the contact object
});
});

To update a property in an embedded object, modify the property in a write transaction:

// Find the contact with the address you want to update
const harryPotter = realm
.objects("Contact")
.filtered("name = 'Harry Potter'")[0];
// modify the property of the embedded object in a write transaction
realm.write(() => {
// update the embedded object directly through the contact
harryPotter.address.street = "1 Hogwarts Ave";
});

To overwrite an embedded object, reassign the embedded object property of a party to a new instance in a write transaction:

// create a new address
const harryNewAddress = {
street: "12 Grimmauld Place",
city: "London",
country: "UK",
postalCode: "E1 7AA",
};
realm.write(() => {
// overwrite the embedded object with the new address within a write transaction
harryPotter.address = harryNewAddress;
});

Use dot notation to filter or sort a collection of objects based on an embedded object property value:

Note

It is not possible to query embedded objects directly. Instead, access embedded objects through a query for the parent object type.

const philipShermanAddress = realm
.objects("Contact")
.filtered("name = 'Philip Sherman'")[0].address.street;
console.log(`Philip Sherman's address is ${philipShermanAddress}`);

Realm Uses Cascading Deletes for Embedded Objects. To delete an embedded object, delete the embedded object's parent.

realm.write(() => {
// Deleting the contact will delete the embedded address of that contact
realm.delete(
realm.objects("Contact").filtered("name = 'Philip Sherman'")
);
});
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