Define a Realm Object Model - Swift SDK

Define a New Object Type

Objective-C

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.

// A dog has an _id primary key, a string name, an optional
// string breed, and a date of birth.
@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"
    ];
}
@end

Swift

You 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.

// A dog has an _id primary key, a string name, an optional
// string breed, and a date of birth.
class Dog: Object {
    @Persisted(primaryKey: true) var _id: ObjectId
    @Persisted var name = ""
    @Persisted var breed: String?
    @Persisted var dateOfBirth = Date()
}

Note: Class names are limited to a maximum of 57 UTF-8 characters.

Declare Properties

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.

Persisted Property Attributes

Version added: 10.10.0The declaration style replaces the , , and declaration notations from older versions of the SDK. For an older version of the SDK, see: .

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.

Seealso: Our Supported Property Types page contains a property declaration cheatsheet.

Objective-C Dynamic Property Attributes

Version changed: 10.10.0This 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.

Version changed: 10.8.0 RealmProperty replaces RealmOptional

Seealso: Our Supported Property Types page contains a property declaration cheatsheet.

Tip: For reference on which types Realm supports for use as properties, see Supported Property Types.

Swift

When declaring non-generic properties, use the @Persisted annotation. The @Persisted attribute turns Realm model properties into accessors for the underlying database data.

Objective-C

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:

// Task.h
@interface Task : RLMObject
@property NSString *description;
@end

// Define an RLMArray<Task> type
RLM_COLLECTION_TYPE(Task)

// User.h
// #include "Task.h"
@interface User : RLMObject
@property NSString *name;
// Use RLMArray<Task> to have a list of tasks
// Note the required double tag (<Task *><Task>)
@property RLMArray<Task *><Task> *tasks;
@end

Swift Pre 10.10.0

When 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 Objective‑C runtime, which Realm uses for dynamic dispatch of dynamic properties.

Note: Property names are limited to a maximum of 63 UTF-8 characters.

Specify an Optional/Required Property

Swift

You can declare properties as optional or required (non-optional) using standard Swift syntax.

class Person: Object {
    // Required string property
    @Persisted var name = ""

    // Optional string property
    @Persisted var address: String?

    // Required numeric property
    @Persisted var ageYears = 0

    // Optional numeric property
    @Persisted var heightCm: Float?
}

Objective-C

To declare a given property as required, implement the requiredProperties method and return an array of required property names.

@interface Person : RLMObject
// Required property - included in `requiredProperties`
// return value array
@property NSString *name;

// Optional string property - not included in `requiredProperties`
@property NSString *address;

// Required numeric property
@property int ageYears;

// Optional numeric properties use NSNumber tagged
// with RLMInt, RLMFloat, etc.
@property NSNumber<RLMFloat> *heightCm;
@end

@implementation Person
// Specify required pointer-type properties here.
// Implicitly required properties (such as properties
// of primitive types) do not need to be named here.
+ (NSArray<NSString *> *)requiredProperties {
    return @[@"name"];
}
@end

Swift Pre 10.10.0

Version changed: 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 {
    // Required string property
    @objc dynamic var name = ""

    // Optional string property
    @objc dynamic var address: String?

    // Required numeric property
    @objc dynamic var ageYears = 0

    // Optional numeric property
    let heightCm = RealmProperty<Float?>()
}

RealmProperty supports Int, Float, Double, Bool, and all of the sized versions of Int (Int8, Int16, Int32, Int64).

Specify a Primary Key

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.

Swift

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 = ""
}

Objective-C

Override +[RLMObject primaryKey] to set the model's primary key.

@interface Project : RLMObject
@property NSInteger id; // Intended primary key
@property NSString *name;
@end

@implementation Project
// Return the name of the primary key property
+ (NSString *)primaryKey {
    return @"id";
}
@end

Swift Pre 10.10.0

Override Object.primaryKey() to set the model's primary key.

class Project: Object {
    @objc dynamic var id = 0
    @objc dynamic var name = ""

    // Return the name of the primary key property
    override static func primaryKey() -> String? {
        return "id"
    }
}

Index a Property

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.

Version added: 10.8.0 UUID and AnyRealmValue types

Swift

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 = ""
}

Objective-C

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
// Return a list of indexed property names
+ (NSArray *)indexedProperties {
    return @[@"title"];
}
@end

Swift Pre 10.10.0

To 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 = ""

    // Return a list of indexed property names
    override static func indexedProperties() -> [String] {
        return ["title"]
    }
}

Ignore a Property

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.

Tip: Realm automatically ignores read-only properties.

Swift

Deprecated:

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 {
    // If some properties are marked as @Persisted,
    // any properties that do not have the @Persisted
    // annotation are automatically ignored.
    var tmpId = 0

    // The @Persisted properties are managed
    @Persisted var firstName = ""
    @Persisted var lastName = ""

    // Read-only properties are automatically ignored
    var name: String {
        return "\(firstName) \(lastName)"
    }

    // If you mix the pre-10.10 property declaration
    // syntax `@objc dynamic` with the 10.10+ @Persisted
    // annotation within a class, `@objc dynamic`
    // properties are ignored.
    @objc dynamic var email = ""
}

Objective-C

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; // read-only properties are automatically ignored
@property NSString *firstName;
@property NSString *lastName;
@end

@implementation Person
+ (NSArray *)ignoredProperties {
    return @[@"tmpId"];
}
- (NSString *)name {
    return [NSString stringWithFormat:@"%@ %@", self.firstName, self.lastName];
}
@end

Swift Pre 10.10.0

If 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 = ""

    // Read-only properties are automatically ignored
    var name: String {
        return "\(firstName) \(lastName)"
    }

    // Return a list of ignored property names
    override static func ignoredProperties() -> [String] {
        return ["tmpId"]
    }
}

Declare Enum Properties

Swift

Version changed: 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.

// Define the enum
enum TaskStatusEnum: String, PersistableEnum {
    case notStarted
    case inProgress
    case complete
}

// To use the enum:
class Task: Object {
    @Persisted var name: String = ""
    @Persisted var owner: String?

    // Required enum property
    @Persisted var status = TaskStatusEnum.notStarted

    // Optional enum property
    @Persisted var optionalTaskStatusEnumProperty: TaskStatusEnum?
}

Swift Pre 10.10.0

Realm supports only Int-backed @objc enums.

// Define the enum
@objc enum TaskStatusEnum: Int, RealmEnum {
    case notStarted = 1
    case inProgress = 2
    case complete = 3
}

// To use the enum:
class Task: Object {
    @objc dynamic var name: String = ""
    @objc dynamic var owner: String?

    // Required enum property
    @objc dynamic var status = TaskStatusEnum.notStarted
    // Optional enum property
    let optionalTaskStatusEnumProperty = RealmProperty<TaskStatusEnum?>()
}

Seealso: RealmEnum

Remap a Property Name

Version added: 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.

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.

class Person: Object {
    @Persisted var firstName = ""
    @Persisted var lastName = ""

    override class public func propertiesMapping() -> [String: String] {
        ["firstName": "first_name",
         "lastName": "last_name"]
    }
}

Define a Class Projection

About These Examples

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 = ""
}

How to Define a Class Projection

Version added: 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.

Note: When you use a List or a MutableSet in a class projection, the type in the class projection should be ProjectedCollection.

class PersonProjection: Projection<Person> {
    @Projected(\Person.firstName) var firstName // Passthrough from original object
    @Projected(\Person.address?.city) var homeCity // Rename and access embedded object property through keypath
    @Projected(\Person.friends.projectTo.firstName) var firstFriendsName: ProjectedCollection<String> // Collection mapping
}

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.

Define Unstructured Data

Version added: 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, 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. 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.

Tip:

• 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.