Prevent Realm from overwriting a property when updating an Object

Question

I've setup a REST API to realm object in iOS. However I've found an issue with creating a favorite flag in my object. I've created a favorite bool, however everytime the object is updated from the API it sets the favorite to default false again. Here I want this flag to not be updated, since the favorite only is stored locally. How can I achieve this?

class Pet: Object{     dynamic var id: Int = 1     dynamic var title: String = ""     dynamic var type: String = ""     dynamic var favorite: Bool = false       override class func primaryKey() -> String {         return "id"     } } 

CreateOrUpdate

let pet = Pet() pet.id = 2 pet.name = "Dog" pet.type = "German Shephard"   try! realm.write {     realm.add(pet, update: true) } 

Answer 1

There are two ways to solve this:

1. Use an Ignored Property:

You can tell Realm that a certain property should not be persisted. To prevent that your favorite property will be persisted by Realm you have to do this:

class Pet: Object{     dynamic var id: Int = 1     dynamic var title: String = ""     dynamic var type: String = ""     dynamic var favorite: Bool = false      override class func primaryKey() -> String {         return "id"     }      override static func ignoredProperties() -> [String] {        return ["favorite"]    } } 

or you could

2. Do a partial update

Or you could tell Realm explicitly which properties should be updated when you update your Pet object:

try! realm.write {   realm.create(Pet.self, value: ["id": 2, "name": "Dog", "type": "German Shepard"], update: true) } 

This way the favorite property will not be changed.

Conclusion

There is one big difference between the two approaches:

Ignored Property: Realm won't store the favorite property at all. It is your responsibility to keep track of them.

Partial Update: Realm will store the 'favorite' property, but it won't be updated.

I suppose that the partial updates are what you need for your purpose.

Answer 2

If you want to be more explicit, there is third option:

3. Retrieve the current value for the update

// Using the add/update method let pet = Pet() pet.id = 2 pet.name = "Dog" pet.type = "German Shephard"  if let currentObject = realm.object(ofType: Pet.self, forPrimaryKey: 2) {     pet.favorite = currentObject.favorite }  try! realm.write {     realm.add(pet, update: true) }  // Using the create/update method var favorite = false if let currentObject = realm.object(ofType: Pet.self, forPrimaryKey: 2) {     favorite = currentObject.favorite }  // Other properties on the pet, such as a list will remain unchanged try! realm.write {     realm.create(Pet.self, value: ["id": 2, "name": "Dog", "type": "German Shephard", "favorite": favorite], update: true) }