You can define a Realm object by deriving from the RLMObject or RLMEmbeddedObject class. The name of the class becomes the table name in the realm, and properties of the class persist in the database. This makes it as easy to work with persisted objects as it is to work with regular Objective-C objects.
@interface Dog : RLMObject@property RLMObjectId *_id;@property NSString *name;@property NSString *breed;@property NSDate *dateOfBirth;@end@implementation Dog+ (NSString *)primaryKey { return @"_id";}+ (NSArray<NSString *> *)requiredProperties { return @[ @"_id", @"name", @"dateOfBirth" ];}@endYou can define a Realm object by deriving from the Object or EmbeddedObject class. The name of the class becomes the table name in the realm, and properties of the class persist in the database. This makes it as easy to work with persisted objects as it is to work with regular Swift objects.
class Dog: Object { @Persisted(primaryKey: true) var _id: ObjectId @Persisted var name = "" @Persisted var breed: String? @Persisted var dateOfBirth = Date()}Class names are limited to a maximum of 57 UTF-8 characters.
When you declare the property attributes of a class, you can specify whether or not those properties should be managed by the realm. Managed properties are stored or updated in the database. Ignored properties are not stored to the database. You can mix managed and ignored properties within a class.
The syntax to mark properties as managed or ignored varies depending on which version of the SDK you use.
New in version 10.10.0: The @Persisted declaration style replaces the @objc dynamic, RealmOptional, and RealmProperty declaration notations from older versions of the SDK. For an older version of the SDK, see: Objective-C Dynamic Property Attributes.
Declare model properties that you want to store to the database as @Persisted. This enables them to access the underlying database data.
When you declare any properties as @Persisted within a class, the other properties within that class are automatically ignored.
If you mix @Persisted and @objc dynamic property declarations within a class definition, any property attributes marked as @objc dynamic will be ignored.
Changed in version 10.10.0: This property declaration information is for versions of the SDK before 10.10.0.
Declare dynamic Realm model properties in the Objective-C runtime. This enables them to access the underlying database data.
You can either:
Use @objc dynamic var to declare individual properties
Use @objcMembers to declare a class. Then, declare individual properties with dynamic var.
Use let to declare LinkingObjects, List, RealmOptional and RealmProperty. The Objective-C runtime cannot represent these generic properties.
Changed in version 10.8.0: RealmProperty replaces RealmOptional
When declaring non-generic properties, use the @Persisted annotation. The @Persisted attribute turns Realm model properties into accessors for the underlying database data.
Declare properties on your object type as you would on a normal Objective-C interface.
In order to use your interface in a Realm array, pass your interface name to the RLM_COLLECTION_TYPE() macro. You can put this at the bottom of your interface's header file. The RLM_COLLECTION_TYPE() macro creates a protocol that allows you to tag RLMArray with your type:
@interface Task : RLMObject@property NSString *description;@endRLM_COLLECTION_TYPE(Task)@interface User : RLMObject@property NSString *name;@property RLMArray<Task *><Task> *tasks;@endWhen declaring non-generic properties, use the @objc dynamic var annotation. The @objc dynamic var attribute turns Realm model properties into accessors for the underlying database data. If the class is declared as @objcMembers (Swift 4 or later), you can declare properties as dynamic var without @objc.
To declare properties of generic types LinkingObjects, List, and RealmProperty, use let. Generic properties cannot be represented in the ObjectiveâC runtime, which Realm uses for dynamic dispatch of dynamic properties.
Property names are limited to a maximum of 63 UTF-8 characters.
You can declare properties as optional or required (non-optional) using standard Swift syntax.
class Person: Object { @Persisted var name = "" @Persisted var address: String? @Persisted var ageYears = 0 @Persisted var heightCm: Float?}To declare a given property as required, implement the requiredProperties method and return an array of required property names.
@interface Person : RLMObject@property NSString *name;@property NSString *address;@property int ageYears;@property NSNumber<RLMFloat> *heightCm;@end@implementation Person+ (NSArray<NSString *> *)requiredProperties { return @[@"name"];}@endChanged in version 10.8.0: RealmProperty replaces RealmOptional
You can declare String, Date, Data, and ObjectId properties as optional or required (non-optional) using standard Swift syntax. Declare optional numeric types using the RealmProperty type.
class Person: Object { @objc dynamic var name = "" @objc dynamic var address: String? @objc dynamic var ageYears = 0 let heightCm = RealmProperty<Float?>()}RealmProperty supports Int, Float, Double, Bool, and all of the sized versions of Int (Int8, Int16, Int32, Int64).
You can designate a property as the primary key of your class.
Primary keys allow you to efficiently find, update, and upsert objects.
Primary keys are subject to the following limitations:
You can define only one primary key per object model.
Primary key values must be unique across all instances of an object in a realm. Realm throws an error if you try to insert a duplicate primary key value.
Primary key values are immutable. To change the primary key value of an object, you must delete the original object and insert a new object with a different primary key value.
Embedded objects cannot define a primary key.
Declare the property with primaryKey: true on the @Persisted notation to set the model's primary key.
class Project: Object { @Persisted(primaryKey: true) var id = 0 @Persisted var name = ""}Override +[RLMObject primaryKey] to set the model's primary key.
@interface Project : RLMObject@property NSInteger id; @property NSString *name;@end@implementation Project+ (NSString *)primaryKey { return @"id";}@endOverride Object.primaryKey() to set the model's primary key.
class Project: Object { @objc dynamic var id = 0 @objc dynamic var name = "" override static func primaryKey() -> String? { return "id" }}You can create an index on a given property of your model. Indexes speed up queries using equality and IN operators. They make insert and update operation speed slightly slower. Indexes use memory and take up more space in the realm file. Each index entry is a minimum of 12 bytes. It's best to only add indexes when optimizing the read performance for specific situations.
Realm supports indexing for string, integer, boolean, Date, UUID, ObjectId, and AnyRealmValue properties.
New in version 10.8.0: UUID and AnyRealmValue types
To index a property, declare the property with indexed:true on the @Persisted notation.
class Book: Object { @Persisted var priceCents = 0 @Persisted(indexed: true) var title = ""}To index a property, override +[RLMObject indexedProperties] and return a list of indexed property names.
@interface Book : RLMObject@property int priceCents;@property NSString *title;@end@implementation Book+ (NSArray *)indexedProperties { return @[@"title"];}@endTo index a property, override Object.indexedProperties() and return a list of indexed property names.
class Book: Object { @objc dynamic var priceCents = 0 @objc dynamic var title = "" override static func indexedProperties() -> [String] { return ["title"] }}Ignored properties behave exactly like normal properties. They can't be used in queries and won't trigger Realm notifications. You can still observe them using KVO.
TipRealm automatically ignores read-only properties.
Deprecated since version 10.10.0: ignoredProperties()
If you don't want to save a field in your model to its realm, leave the @Persisted notation off the property attribute.
Additionally, if you mix @Persisted and @objc dynamic property declarations within a class, the @objc dynamic properties will be ignored.
class Person: Object { var tmpId = 0 @Persisted var firstName = "" @Persisted var lastName = "" var name: String { return "\(firstName) \(lastName)" } @objc dynamic var email = ""}If you don't want to save a field in your model to its realm, override +[RLMObject ignoredProperties] and return a list of ignored property names.
@interface Person : RLMObject@property NSInteger tmpId;@property (readonly) NSString *name; @property NSString *firstName;@property NSString *lastName;@end@implementation Person+ (NSArray *)ignoredProperties { return @[@"tmpId"];}- (NSString *)name { return [NSString stringWithFormat:@"%@ %@", self.firstName, self.lastName];}@endIf you don't want to save a field in your model to its realm, override Object.ignoredProperties() and return a list of ignored property names.
class Person: Object { @objc dynamic var tmpId = 0 @objc dynamic var firstName = "" @objc dynamic var lastName = "" var name: String { return "\(firstName) \(lastName)" } override static func ignoredProperties() -> [String] { return ["tmpId"] }}Changed in version 10.10.0: Protocol is now PersistableEnum rather than RealmEnum.
You can use enums with @Persisted by marking them as complying with the PersistableEnum protocol. A PersistableEnum can be any RawRepresentable enum whose raw type is a type that Realm supports.
enum TaskStatusEnum: String, PersistableEnum { case notStarted case inProgress case complete}class Task: Object { @Persisted var name: String = "" @Persisted var owner: String? @Persisted var status = TaskStatusEnum.notStarted @Persisted var optionalTaskStatusEnumProperty: TaskStatusEnum? }Realm supports only Int-backed @objc enums.
@objc enum TaskStatusEnum: Int, RealmEnum { case notStarted = 1 case inProgress = 2 case complete = 3}class Task: Object { @objc dynamic var name: String = "" @objc dynamic var owner: String? @objc dynamic var status = TaskStatusEnum.notStarted let optionalTaskStatusEnumProperty = RealmProperty<TaskStatusEnum?>() }New in version 10.33.0.
You can map the public name of a property in your object model to a different private name to store in the realm. You might want to do this if your Device Sync schema property names use snake case, for example, while your project uses Swift-idiomatic camel case.
Declare the name you want to use in your project as the @Persisted property on the object model. Then, pass a dictionary containing the public and private values for the property names via the propertiesMapping() function.
In this example, firstName is the public property name we use in the code throughout the project to perform CRUD operations. Using the propertiesMapping() function, we map that to store values using the private property name first_name in the realm. If we write to a synced realm, the Sync schema sees the values stored using the private property name first_name.
class Person: Object { @Persisted var firstName = "" @Persisted var lastName = "" override class public func propertiesMapping() -> [String: String] { ["firstName": "first_name", "lastName": "last_name"] }}The examples in this section use a simple data set. The two Realm object types are Person and an embedded object Address. A Person has a first and last name, an optional Address, and a list of friends consisting of other Person objects. An Address has a city and country.
See the schema for these two classes, Person and Address, below:
class Person: Object { @Persisted var firstName = "" @Persisted var lastName = "" @Persisted var address: Address? @Persisted var friends = List<Person>()}class Address: EmbeddedObject { @Persisted var city: String = "" @Persisted var country = ""}New in version 10.21.0.
Define a class projection by creating a class of type Projection. Specify the Object or EmbeddedObject base whose properties you want to use in the class projection. Use the @Projected property wrapper to declare a property that you want to project from a @Persisted property on the base object.
class PersonProjection: Projection<Person> { @Projected(\Person.firstName) var firstName @Projected(\Person.address?.city) var homeCity @Projected(\Person.friends.projectTo.firstName) var firstFriendsName: ProjectedCollection<String> }When you define a class projection, you can transform the original @Persisted property in several ways:
Passthrough: the property is the same name and type as the original object
Rename: the property has the same type as the original object, but a different name
Keypath resolution: use keypath resolution to access properties of the original object, including embedded object properties
Collection mapping: Project lists or mutable sets of Object s or EmbeddedObject s as a collection of primitive values
Exclusion: when you use a class projection, the underlying object's properties that are not @Projected through the class projection are excluded. This enables you to watch for changes to a class projection and not see changes for properties that are not part of the class projection.
New in version 10.29.0.
If your app uses Flexible Sync, you can use Data Ingest to sync an object unidirectionally from your device to the database linked to your Atlas App Services App. Define an asymmetric object by inheriting from AsymmetricObject.
class WeatherSensor: AsymmetricObject { @Persisted(primaryKey: true) var _id: ObjectId @Persisted var deviceId: String @Persisted var temperatureInFahrenheit: Float @Persisted var barometricPressureInHg: Float @Persisted var windSpeedInMph: Int}Changed in version 10.42.4: Asymmetric objects can link to non-embedded objects.
AsymmetricObject broadly supports the same property types as Object, with a few exceptions:
Object and List<Object> properties are not supported in Swift SDK versions 10.42.3 and earlier. In Swift SDK versions 10.42.4 and later, asymmetric objects can link to non-embedded objects.
EmbeddedObject and List<EmbeddedObject> are supported.
You cannot link to an AsymmetricObject from within an Object. Doing so throws an error.
Asymmetric objects do not function in the same way as other Realm Objects. You cannot:
Add an asymmetric object to a realm
Remove an asymmetric object from a realm
Query an asymmetric object
You can only create an Asymmetric object, which then syncs unidirectionally to the Atlas database linked to your App with Device Sync.
For more information, see: Create an Asymmetric Object.
New in version 10.51.0.
Starting in SDK version 10.51.0, you can store collections of mixed data within a AnyRealmValue property. You can use this feature to model complex data structures, such as JSON or MongoDB documents, without having to define a strict data model.
Unstructured data is data that doesn't easily conform to an expected schema, making it difficult or impractical to model to individual data classes. For example, your app might have highly variable data or dynamic data whose structure is unknown at runtime.
Storing collections in a mixed property offers flexibility without sacrificing functionality, including performant synchronization when using Device Sync. And you can work with them the same way you would a non-mixed collection:
You can nest mixed collections up to 100 levels.
You can query on and react to changes on mixed collections.
You can find and update individual mixed collection elements.
However, storing data in mixed collections is less performant than using a structured schema or serializing JSON blobs into a single string property.
To model unstructured data in your app, define the appropriate properties in your schema as AnyRealmValue types. You can then set these AnyRealmValue properties as a list or a dictionary collection of AnyRealmValue elements. Note that AnyRealmValue cannot represent a MutableSet or an embedded object.
Use a map of mixed data types when the type is unknown but each value will have a unique identifier.
Use a list of mixed data types when the type is unknown but the order of objects is meaningful.
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