Embedded Objects - Java SDK
On this page
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 of a single, specific parent object. An embedded object inherits the lifecycle of its parent object and cannot exist as an independent Realm object. Realm automatically deletes embedded objects if their parent object is deleted or when overwritten by a new embedded object instance.
Warning
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.
Embedded Object Data Models
You can define embedded object types using either Realm object models or a server-side document schema. 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 of other embedded objects.
Important
Embedded objects cannot have a primary key.
Realm Object Models
To define an embedded object, derive a class from RealmObject and set the embedded property of the
RealmClass annotation
to true. You can reference an embedded object type from parent
object types in the same way as you would define a relationship:
// Define an embedded object public class Address extends RealmObject { String street; String city; String country; String postalCode; public Address(String street, String city, String country, String postalCode) { this.street = street; this.city = city; this.country = country; this.postalCode = postalCode; } public Address() {} } // Define an object containing one embedded object public class Contact extends RealmObject { private ObjectId _id = new ObjectId(); String name = ""; // Embed a single object. // Embedded object properties must be marked optional Address address; public Contact(String name, Address address) { this.name = name; this.address = address; } public Contact() {} } // Define an object containing an array of embedded objects public class Business extends RealmObject { private ObjectId _id = new ObjectId(); String name = ""; // Embed an array of objects RealmList<Address> addresses = new RealmList<Address>(); public Business(String name, RealmList<Address> addresses) { this.name = name; this.addresses = addresses; } public Business() {} }
// Define an embedded object open class Address( var street: String? = null, var city: String? = null, var country: String? = null, var postalCode: String? = null ): RealmObject() {} // Define an object containing one embedded object open class Contact(_name: String = "", _address: Address? = null) : RealmObject() { var _id: ObjectId = ObjectId() var name: String = _name // Embed a single object. // Embedded object properties must be marked optional var address: Address? = _address } // Define an object containing an array of embedded objects open class Business(_name: String = "", _addresses: RealmList<Address> = RealmList()) : RealmObject() { var _id: ObjectId = ObjectId() var name: String = _name // Embed an array of objects var addresses: RealmList<Address> = _addresses }
JSON Schema
Embedded objects map to embedded documents in the parent type's schema. This behavior differs from regular Realm objects, which map to their own MongoDB collection.
{ "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"], "properties": { "_id": { "bsonType": "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" } } } } } }
Read and Write Embedded Objects
Create an Embedded Object
To create an embedded object, assign an instance of the embedded object to a parent object's property:
User user = app.currentUser(); String partitionValue = "My Project"; SyncConfiguration config = new SyncConfiguration.Builder(user, partitionValue) .build(); Realm realm = Realm.getInstance(config); Address address = new Address("123 Fake St.", "Springfield", "USA", "90710"); Contact contact = new Contact("Nick Riviera", address); realm.executeTransaction(transactionRealm -> { transactionRealm.insert(contact); }); realm.close();
val user: User? = app.currentUser() val partitionValue: String = "<partition>" // replace this with a partition key val config = SyncConfiguration.Builder(user!!, partitionValue) .build() val realm: Realm = Realm.getInstance(config) val address = Address("123 Fake St.", "Springfield", "USA", "90710") val contact = Contact("Nick Riviera", address) realm.executeTransaction { transactionRealm -> transactionRealm.insert(contact) } realm.close()
Update an Embedded Object Property
To update a property in an embedded object, modify the property in a write transaction:
// assumes that at least one contact already exists in this partition Contact resultContact = realm.where(Contact.class).findFirst(); realm.executeTransaction(transactionRealm -> { resultContact.address.street = "Hollywood Upstairs Medical College"; resultContact.address.city = "Los Angeles"; resultContact.address.postalCode = "90210"; Log.v("EXAMPLE", "Updated contact: " + resultContact); }); realm.close();
// assumes that at least one contact already exists in this partition val result = realm.where<Contact>().findFirst()!! realm.executeTransaction { transactionRealm -> result.address?.street = "Hollywood Upstairs Medical College" result.address?.city = "Los Angeles" result.address?.postalCode = "90210" Log.v("EXAMPLE", "Updated contact: ${result.name}") } realm.close()
Overwrite an Embedded Object
To overwrite an embedded object, reassign the embedded object property of a party to a new instance in a write transaction:
// assumes that at least one contact already exists in this partition Contact oldContact = realm.where(Contact.class).findFirst(); realm.executeTransaction(transactionRealm -> { Address newAddress = new Address( "Hollywood Upstairs Medical College", "Los Angeles", "USA" "90210" ); oldContact.address = newAddress; Log.v("EXAMPLE", "Replaced contact: " + oldContact); }); realm.close();
// assumes that at least one contact already exists in this partition val oldContact = realm.where<Contact>().findFirst()!! realm.executeTransaction { transactionRealm -> val newAddress = Address( "Hollywood Upstairs Medical College", "Los Angeles", "USA", "90210") oldContact.address = newAddress Log.v("EXAMPLE", "Updated contact: $oldContact") } realm.close()
Query a Collection on Embedded Object Properties
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.
RealmResults<Contact> losAngelesContacts = realm.where(Contact.class) .equalTo("address.city", "Los Angeles") .sort("address.street").findAll(); Log.v("EXAMPLE", "Los Angeles contacts: " + losAngelesContacts);
val losAngelesContacts = realm.where<Contact>() .equalTo("address.city", "Los Angeles") .sort("address.street").findAll() Log.v("EXAMPLE", "Los Angeles Contacts: $losAngelesContacts")