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CRUD - Update - Swift SDK

On this page

  • Update Realm Objects
  • About The Examples On This Page
  • Update an Object
  • Update Properties with Key-value Coding
  • Upsert an Object
  • Update a Map/Dictionary
  • Update a MutableSet Property
  • Update an AnyRealmValue Property
  • Update an Embedded Object Property
  • Overwrite an Embedded Object
  • Update an Object Asynchronously
  • Update Properties through Class Projections
  • Change Class Projection Properties

Updates to Realm Objects must occur within write transactions. For more information about write transactions, see: Transactions.

The examples on this page use the following models:

You can modify properties of a Realm object inside of a write transaction in the same way that you would update any other Swift or Objective-C object.


Update Related and Embedded Objects

To update a property of an embedded object or a related object, modify the property with dot-notation or bracket-notation as if it were in a regular, nested object.

Object, Result, and List all conform to key-value coding. This can be useful when you need to determine which property to update at runtime.

Applying KVC to a collection is a great way to update objects in bulk. Avoid the overhead of iterating over a collection while creating accessors for every item.

let realm = try! Realm()
let allDogs = realm.objects(Dog.self)
try! realm.write {
allDogs.first?.setValue("Sparky", forKey: "name")
// Move the dogs to Toronto for vacation
allDogs.setValue("Toronto", forKey: "currentCity")

You can also add values for embedded objects or relationships this way. In this example, we add a collection to an object's list property:

An upsert either inserts or updates an object depending on whether the object already exists. Upserts require the data model to have a primary key.

You can also partially update an object by passing the primary key and a subset of the values to update:

You can update a realm map as you would a standard Dictionary:

let realm = try! Realm()
// Find the dog we want to update
let wolfie = realm.objects(Dog.self).where {
$ == "Wolfie"
print("Wolfie's favorite park in New York is: \(wolfie.favoriteParksByCity["New York"])")
XCTAssertTrue(wolfie.favoriteParksByCity["New York"] == "Domino Park")
// Update values for keys, or add values if the keys do not currently exist
try! realm.write {
wolfie.favoriteParksByCity["New York"] = "Washington Square Park"
wolfie.favoriteParksByCity.updateValue("A Street Park", forKey: "Boston")
wolfie.favoriteParksByCity.setValue("Little Long Pond", forKey: "Seal Harbor")
XCTAssertTrue(wolfie.favoriteParksByCity["New York"] == "Washington Square Park")

You can insert elements into a MutableSet during write transactions to add them to the property. If you are working with multiple sets, you can also insert or remove set elements contained in one set from the other set. Alternately, you can mutate a set to contain only the common elements from both.

let realm = try! Realm()
// Record a dog's name, current city, and store it to the cities visited.
let dog = Dog() = "Maui"
dog.currentCity = "New York"
try! realm.write {
// Update the dog's current city, and add it to the set of cities visited.
try! realm.write {
dog.currentCity = "Toronto"
XCTAssertEqual(dog.citiesVisited.count, 2)
// If you're operating with two sets, you can insert the elements from one set into another set.
// The dog2 set contains one element that isn't present in the dog set.
try! realm.write {
XCTAssertEqual(dog.citiesVisited.count, 3)
// Or you can remove elements that are present in the second set. This removes the one element
// that we added above from the dog2 set.
try! realm.write {
XCTAssertEqual(dog.citiesVisited.count, 2)
// If the sets contain common elements, you can mutate the set to only contain those common elements.
// In this case, the two sets contain no common elements, so this set should now contain 0 items.
try! realm.write {
XCTAssertEqual(dog.citiesVisited.count, 0)

You can update an AnyRealmValue property through assignment, but you must specify the type of the value when you assign it. The Realm Swift SDK provides an AnyRealmValue enum that iterates through all of the types the AnyRealmValue can store.

let realm = try! Realm()
// Get a dog to update
let rex = realm.objects(Dog.self).where {
$ == "Rex"
try! realm.write {
// As with creating an object with an AnyRealmValue, you must specify the
// type of the value when you update the property.
rex.companion = .object(Dog(value: ["name": "Regina"]))

To update a property in an embedded object, modify the property in a write transaction. If the embedded object is null, updating an embedded object property has no effect.

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

You can use Swift concurrency features to asynchronously update objects using an actor-isolated realm.

This function from the example RealmActor defined on the Use Realm with Actors page shows how you might update an object in an actor-isolated realm:

func updateTodo(_id: ObjectId, name: String, owner: String, status: String) async throws {
try await realm.asyncWrite {
realm.create(Todo.self, value: [
"_id": _id,
"name": name,
"owner": owner,
"status": status
], update: .modified)

And you might perform this update using Swift's async syntax:

let actor = try await RealmActor()
// Read objects in functions isolated to the actor and pass primitive values to the caller
func getObjectId(in actor: isolated RealmActor, forTodoNamed name: String) async -> ObjectId {
let todo = actor.realm.objects(Todo.self).where {
$ == name
return todo._id
let objectId = await getObjectId(in: actor, forTodoNamed: "Keep it safe")
try await actor.updateTodo(_id: objectId, name: "Keep it safe", owner: "Frodo", status: "Completed")

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.

You can make changes to a class projection's properties in a write transaction.

// Retrieve all class projections of the given type `PersonProjection`
// and filter for the first class projection where the `firstName` property
// value is "Jason"
let person = realm.objects(PersonProjection.self).first(where: { $0.firstName == "Jason" })!
// Update class projection property in a write transaction
try! realm.write {
person.firstName = "David"
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