CRUD - Create - Swift SDK
On this page
- Create a New Object
- About The Examples On This Page
- Create an Object
- Initialize Objects with a Value
- Create an Object with JSON
- Create an Embedded Object
- Create an Object with a Map Property
- Create an Object with a MutableSet Property
- Create an Object with an AnyRealmValue Property
- Create an Object Asynchronously
- Create an Asymmetric Object
- Copy an Object to Another Realm
Create a New Object
About The Examples On This Page
The examples on this page use the following models:
// DogToy.h @interface DogToy : RLMObject @property NSString *name; @end // Dog.h @interface Dog : RLMObject @property NSString *name; @property int age; @property NSString *color; // To-one relationship @property DogToy *favoriteToy; @end // Enable Dog for use in RLMArray RLM_COLLECTION_TYPE(Dog) // Person.h // A person has a primary key ID, a collection of dogs, and can be a member of multiple clubs. @interface Person : RLMObject @property int _id; @property NSString *name; // To-many relationship - a person can have many dogs @property RLMArray<Dog *><Dog> *dogs; // Inverse relationship - a person can be a member of many clubs @property (readonly) RLMLinkingObjects *clubs; @end RLM_COLLECTION_TYPE(Person) // DogClub.h @interface DogClub : RLMObject @property NSString *name; @property RLMArray<Person *><Person> *members; @end // Dog.m @implementation Dog @end // DogToy.m @implementation DogToy @end // Person.m @implementation Person // Define the primary key for the class + (NSString *)primaryKey { return @"_id"; } // Define the inverse relationship to dog clubs + (NSDictionary *)linkingObjectsProperties { return @{ @"clubs": [RLMPropertyDescriptor descriptorWithClass:DogClub.class propertyName:@"members"], }; } @end // DogClub.m @implementation DogClub @end
class DogToy: Object { var name = "" } class Dog: Object { var name = "" var age = 0 var color = "" var currentCity = "" var citiesVisited: MutableSet<String> var companion: AnyRealmValue // To-one relationship var favoriteToy: DogToy? // Map of city name -> favorite park in that city var favoriteParksByCity: Map<String, String> } class Person: Object { true) var id = 0 (primaryKey: var name = "" // To-many relationship - a person can have many dogs var dogs: List<Dog> // Embed a single object. // Embedded object properties must be marked optional. var address: Address? convenience init(name: String, address: Address) { self.init() self.name = name self.address = address } } class Address: EmbeddedObject { var street: String? var city: String? var country: String? var postalCode: String? }
Create an Object
To add an object to a realm, instantiate it as you would any other object and then pass it to -[RLMRealm addObject:] inside of a write transaction.
// Get the default realm. // You only need to do this once per thread. RLMRealm *realm = [RLMRealm defaultRealm]; // Instantiate the class. Dog *dog = [[Dog alloc] init]; dog.name = @"Max"; dog.age = 5; // Open a thread-safe transaction. [realm transactionWithBlock:^() { // Add the instance to the realm. [realm addObject:dog]; }];
To add an object to a realm, instantiate it as you would any other object and then pass it to Realm.add(_:update:) inside of a write transaction.
// Instantiate the class and set its values. let dog = Dog() dog.name = "Rex" dog.age = 10 // Get the default realm. You only need to do this once per thread. let realm = try! Realm() // Open a thread-safe transaction. try! realm.write { // Add the instance to the realm. realm.add(dog) }
Initialize Objects with a Value
You can initialize an object by passing an initializer value to Object.init(value:). The initializer value can be a key-value coding compliant object, a dictionary, or an array containing one element for each managed property.
Note
When using an array as an initializer value, you must include all properties in the same order as they are defined in the model.
// (1) Create a Dog object from a dictionary Dog *myDog = [[Dog alloc] initWithValue:@{@"name" : @"Pluto", @"age" : @3}]; // (2) Create a Dog object from an array Dog *myOtherDog = [[Dog alloc] initWithValue:@[@"Pluto", @3]]; RLMRealm *realm = [RLMRealm defaultRealm]; // Add to the realm with transaction [realm transactionWithBlock:^() { [realm addObject:myDog]; [realm addObject:myOtherDog]; }];
// (1) Create a Dog object from a dictionary let myDog = Dog(value: ["name": "Pluto", "age": 3]) // (2) Create a Dog object from an array let myOtherDog = Dog(value: ["Fido", 5]) let realm = try! Realm() // Add to the realm inside a transaction try! realm.write { realm.add([myDog, myOtherDog]) }
You can even initialize related or embedded objects by nesting initializer values:
// Instead of using pre-existing dogs... Person *aPerson = [[Person alloc] initWithValue:@[@123, @"Jane", @[aDog, anotherDog]]]; // ...we can create them inline Person *anotherPerson = [[Person alloc] initWithValue:@[@123, @"Jane", @[@[@"Buster", @5], @[@"Buddy", @6]]]];
// Instead of using pre-existing dogs... let aPerson = Person(value: [123, "Jane", [aDog, anotherDog]]) // ...we can create them inline let anotherPerson = Person(value: [123, "Jane", [["Buster", 5], ["Buddy", 6]]])
Some Property Types are Only Mutable in a Write Transaction
Some property types are only mutable in a write transaction. For example, you can instantiate an object with a MutableSet property, but you can only set that property's value in a write transaction. You cannot initialize the object with a value for that property unless you do so inside a write transaction.
Create an Object with JSON
Realm does not directly support JSON, but you can use JSONSerialization.jsonObject(with:options:) to convert JSON into a value that you can pass to Realm.create(_:value:update:).
// Specify a dog toy in JSON NSData *data = [@"{\"name\": \"Tennis ball\"}" dataUsingEncoding: NSUTF8StringEncoding]; RLMRealm *realm = [RLMRealm defaultRealm]; // Insert from NSData containing JSON [realm transactionWithBlock:^{ id json = [NSJSONSerialization JSONObjectWithData:data options:0 error:NULL]; [DogToy createInRealm:realm withValue:json]; }];
// Specify a dog toy in JSON let data = "{\"name\": \"Tennis ball\"}".data(using: .utf8)! let realm = try! Realm() // Insert from data containing JSON try! realm.write { let json = try! JSONSerialization.jsonObject(with: data, options: []) realm.create(DogToy.self, value: json) }
Nested objects or arrays in the JSON map to to-one or to-many relationships.
The JSON property names and types must match the destination object schema exactly. For example:
float
properties must be initialized with float-backedNSNumbers
.Date
andData
properties cannot be inferred from strings. Convert them to the appropriate type before passing to Realm.create(_:value:update:).Required properties cannot be
null
or missing in the JSON.
Realm ignores any properties in the JSON not defined in the object schema.
Tip
If your JSON schema doesn't exactly align with your Realm objects, consider using a third-party framework to transform your JSON. There are many model mapping frameworks that work with Realm. See a partial list in the realm-swift repository.
Create an Embedded Object
To create an embedded object, assign an instance of the embedded object to a parent object's property:
RLMRealm *realm = [RLMRealm defaultRealm]; [realm transactionWithBlock:^{ Address *address = [[Address alloc] init]; address.street = @"123 Fake St."; address.city = @"Springfield"; address.country = @"USA"; address.postalCode = @"90710"; Contact *contact = [Contact contactWithName:@"Nick Riviera"]; // Assign the embedded object property contact.address = address; [realm addObject:contact]; NSLog(@"Added contact: %@", contact); }];
// Open the default realm let realm = try! Realm() try! realm.write { let address = Address() address.street = "123 Fake St" address.city = "Springfield" address.country = "USA" address.postalCode = "90710" let contact = Person(name: "Nick Riviera", address: address) realm.add(contact) }
Create an Object with a Map Property
When you create an object that has a map property, you can set the values for keys in a few ways:
Set keys and values on the object and then add the object to the realm
Set the object's keys and values directly inside a write transaction
Use key-value coding to set or update keys and values inside a write transaction
let realm = try! Realm() // Record a dog's name and current city let dog = Dog() dog.name = "Wolfie" dog.currentCity = "New York" // Set map values dog.favoriteParksByCity["New York"] = "Domino Park" // Store the data in a realm try! realm.write { realm.add(dog) // You can also set map values inside a write transaction dog.favoriteParksByCity["Chicago"] = "Wiggly Field" dog.favoriteParksByCity.setValue("Bush Park", forKey: "Ottawa") }
Realm disallows the use of .
or $
characters in map keys.
You can use percent encoding and decoding to store a map key that contains
one of these disallowed characters.
// Percent encode . or $ characters to use them in map keys let mapKey = "New York.Brooklyn" let encodedMapKey = "New York%2EBrooklyn"
Create an Object with a MutableSet Property
You can create objects that contain MutableSet properties as you would any Realm object, but you can only mutate a MutableSet within a write transaction. This means you can only set the value(s) of a mutable set property within a write transaction.
let realm = try! Realm() // Record a dog's name and current city let dog = Dog() dog.name = "Maui" dog.currentCity = "New York" // Store the data in a realm. Add the dog's current city // to the citiesVisited MutableSet try! realm.write { realm.add(dog) // You can only mutate the MutableSet in a write transaction. // This means you can't set values at initialization, but must do it during a write. dog.citiesVisited.insert(dog.currentCity) } // You can also add multiple items to the set. try! realm.write { dog.citiesVisited.insert(objectsIn: ["Boston", "Chicago"]) } print("\(dog.name) has visited: \(dog.citiesVisited)")
Create an Object with an AnyRealmValue Property
When you create an object with an AnyRealmValue property, you must specify the type of the value you store in the property. The Realm Swift SDK provides an AnyRealmValue enum that iterates through all of the types the AnyRealmValue can store.
Later, when you read an AnyRealmValue, you must check the type before you do anything with the value.
// Create a Dog object and then set its properties let myDog = Dog() myDog.name = "Rex" // This dog has no companion. // You can set the field's type to "none", which represents `nil` myDog.companion = .none // Create another Dog whose companion is a cat. // We don't have a Cat object, so we'll use a string to describe the companion. let theirDog = Dog() theirDog.name = "Wolfie" theirDog.companion = .string("Fluffy the Cat") // Another dog might have a dog as a companion. // We do have an object that can represent that, so we can specify the // type is a Dog object, and even set the object's value. let anotherDog = Dog() anotherDog.name = "Fido" // Note: this sets Spot as a companion of Fido, but does not set // Fido as a companion of Spot. Spot has no companion in this instance. anotherDog.companion = .object(Dog(value: ["name": "Spot"])) // Add the dogs to the realm let realm = try! Realm() try! realm.write { realm.add([myDog, theirDog, anotherDog]) } // After adding these dogs to the realm, we now have 4 dog objects. let dogs = realm.objects(Dog.self) XCTAssertEqual(dogs.count, 4)
Create an Object Asynchronously
You can use Swift concurrency features to write asynchronously to an actor-isolated realm.
This function from the example RealmActor
defined on the
Use Realm with Actors page shows how you might
write to an actor-isolated realm:
func createTodo(name: String, owner: String, status: String) async throws { try await realm.asyncWrite { realm.create(Todo.self, value: [ "_id": ObjectId.generate(), "name": name, "owner": owner, "status": status ]) } }
And you might perform this write using Swift's async syntax:
func createObject() async throws { // Because this function is not isolated to this actor, // you must await operations completed on the actor try await actor.createTodo(name: "Take the ring to Mount Doom", owner: "Frodo", status: "In Progress") let taskCount = await actor.count print("The actor currently has \(taskCount) tasks") } let actor = try await RealmActor() try await createObject()
This operation does not block or perform I/O on the calling thread. For more information about writing to realm using Swift concurrency features, refer to Use Realm with Actors - Swift SDK.
Create an Asymmetric Object
New in version 10.29.0.
You can only create an AsymmetricObject using create(_ type:, value:). When you create an AsymmetricObject, it syncs unidirectionally via Data Ingest to the Atlas database linked to your Atlas App Services App. You cannot access an AsymmetricObject locally, add it to or remove it from a realm, or query for it.
func useRealm(_ asymmetricRealm: Realm, _ user: User) async { try! asymmetricRealm.write { asymmetricRealm.create(WeatherSensor.self, value: [ "_id": ObjectId.generate(), "deviceId": "WX1278UIT", "temperatureInFahrenheit": 66.7, "barometricPressureInHg": 29.65, "windSpeedInMph": 2 ]) } }
You can create AsymmetricObjects for a realm initialized with a Flexible Sync configuration. For more information, see: Open a Synced Realm for Flexible Sync.
Copy an Object to Another Realm
To copy an object from one realm to another, pass the original object to +[RLMObject createInRealm:withValue:]:
RLMRealmConfiguration *configuration = [RLMRealmConfiguration defaultConfiguration]; configuration.inMemoryIdentifier = @"first realm"; RLMRealm *realm = [RLMRealm realmWithConfiguration:configuration error:nil]; [realm transactionWithBlock:^{ Dog *dog = [[Dog alloc] init]; dog.name = @"Wolfie"; dog.age = 1; [realm addObject:dog]; }]; // Later, fetch the instance we want to copy Dog *wolfie = [[Dog objectsInRealm:realm where:@"name == 'Wolfie'"] firstObject]; // Open the other realm RLMRealmConfiguration *otherConfiguration = [RLMRealmConfiguration defaultConfiguration]; otherConfiguration.inMemoryIdentifier = @"second realm"; RLMRealm *otherRealm = [RLMRealm realmWithConfiguration:otherConfiguration error:nil]; [otherRealm transactionWithBlock:^{ // Copy to the other realm Dog *wolfieCopy = [[wolfie class] createInRealm:otherRealm withValue:wolfie]; wolfieCopy.age = 2; // Verify that the copy is separate from the original XCTAssertNotEqual(wolfie.age, wolfieCopy.age); }];
To copy an object from one realm to another, pass the original object to Realm.create(_:value:update:)::
let realm = try! Realm(configuration: Realm.Configuration(inMemoryIdentifier: "first realm")) try! realm.write { let dog = Dog() dog.name = "Wolfie" dog.age = 1 realm.add(dog) } // Later, fetch the instance we want to copy let wolfie = realm.objects(Dog.self).first(where: { $0.name == "Wolfie" })! // Open the other realm let otherRealm = try! Realm(configuration: Realm.Configuration(inMemoryIdentifier: "second realm")) try! otherRealm.write { // Copy to the other realm let wolfieCopy = otherRealm.create(type(of: wolfie), value: wolfie) wolfieCopy.age = 2 // Verify that the copy is separate from the original XCTAssertNotEqual(wolfie.age, wolfieCopy.age) }
Important
The create
methods do not support handling cyclical object
graphs. Do not pass in an object containing relationships involving
objects that refer back to their parents, either directly or
indirectly.