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@krodak
Last active April 27, 2023 19:16
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Cascade deletion for RealmSwift
import RealmSwift
import Realm
protocol CascadeDeleting: class {
func delete<Entity>(_ list: List<Entity>, cascading: Bool)
func delete<Entity>(_ results: Results<Entity>, cascading: Bool)
func delete<Entity: Object>(_ entity: Entity, cascading: Bool)
}
extension Realm: CascadeDeleting {
func delete<Entity>(_ list: List<Entity>, cascading: Bool) {
list.forEach {
delete($0, cascading: cascading)
}
}
func delete<Entity>(_ results: Results<Entity>, cascading: Bool) {
results.forEach {
delete($0, cascading: cascading)
}
}
func delete<Entity: Object>(_ entity: Entity, cascading: Bool) {
if cascading {
cascadeDelete(entity)
} else {
delete(entity)
}
}
}
private extension Realm {
private func cascadeDelete(_ entity: RLMObjectBase) {
guard let entity = entity as? Object else { return }
var toBeDeleted = Set<RLMObjectBase>()
toBeDeleted.insert(entity)
while !toBeDeleted.isEmpty {
guard let element = toBeDeleted.removeFirst() as? Object,
!element.isInvalidated else { continue }
resolve(element: element, toBeDeleted: &toBeDeleted)
}
}
private func resolve(element: Object, toBeDeleted: inout Set<RLMObjectBase>) {
element.objectSchema.properties.forEach {
guard let value = element.value(forKey: $0.name) else { return }
if let entity = value as? RLMObjectBase {
toBeDeleted.insert(entity)
} else if let list = value as? RealmSwift.ListBase {
for index in 0..<list._rlmArray.count {
toBeDeleted.insert(list._rlmArray.object(at: index))
}
}
}
delete(element)
}
}
@iSevenDays
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iSevenDays commented Jun 24, 2021

I think the following code should be used, but I am yet to see it in production

internal protocol CascadingDeletable: RealmSwift.Object {
	static var propertiesToCascadeDelete: [String] { get }
}

extension Realm {
	internal func cascadingDelete(_ object: RealmSwift.Object) {
		var toBeDeleted: Set<RLMObjectBase> = [object]
		while let element = toBeDeleted.popFirst() as? RealmSwift.Object {
			guard !element.isInvalidated else { continue }
			if let cascadingDeletable = element as? CascadingDeletable {
				cascade(into: cascadingDeletable, toBeDeleted: &toBeDeleted)
			}
			delete(element)
		}
	}

	private func cascade(into object: CascadingDeletable, toBeDeleted: inout Set<RLMObjectBase>) {
		let objectType = type(of: object)

		guard let schema = objectType.sharedSchema() else { return }

		let primaryKey = objectType.primaryKey()
		let primaryKeyValue = primaryKey.flatMap(object.value(forKey:))

		let properties = (schema.properties + schema.computedProperties)
			.filter { objectType.propertiesToCascadeDelete.contains($0.name) }

		for property in properties {
			switch object.value(forKey: property.name) {
			case let realmObject as RLMObjectBase:
				toBeDeleted.insert(realmObject)
			case let list as RLMSwiftCollectionBase:
				for index in 0 ..< list._rlmCollection.count {
					guard let realmObject = list._rlmCollection.object(at: index) as? RLMObjectBase else { continue }
					toBeDeleted.insert(realmObject)
				}
			default: // LinkingObjects
				if let linkOriginPropertyName = property.linkOriginPropertyName,
				   let linkOriginTypeName = property.objectClassName,
				   let primaryKey = primaryKey,
				   let primaryKeyValue = primaryKeyValue {
					dynamicObjects(linkOriginTypeName)
						.filter("%K == %@", "\(linkOriginPropertyName).\(primaryKey)", primaryKeyValue)
						.forEach { toBeDeleted.insert($0) }
				}
			}
		}
	}
}

@cpd
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cpd commented Aug 5, 2021

Updated code to use RLMSwiftCollectionBase instead of RealmSwift.ListBase which looks fine at first glance but using this hack with latest release seems pretty dangerous, since Realm 10.0 theres a built in cascade delete https://www.mongodb.com/developer/article/realm-database-cascading-deletes/#cascading-deletes probably better to stick with it although I didn't tried that yet.

extension Realm {
    func delete<S: Sequence>(_ objects: S, cascading: Bool) where S.Iterator.Element: Object {
        for obj in objects {
            delete(obj, cascading: cascading)
        }
    }
    
    func delete<Entity: Object>(_ entity: Entity, cascading: Bool) {
        if cascading {
            cascadeDelete(entity)
        } else {
            delete(entity)
        }
    }
}

private extension Realm {
    private func cascadeDelete(_ entity: RLMObjectBase) {
        guard let entity = entity as? Object else { return }
        
        var toBeDeleted = Set<RLMObjectBase>()
        
        toBeDeleted.insert(entity)
        
        while !toBeDeleted.isEmpty {
            guard let element = toBeDeleted.removeFirst() as? Object, !element.isInvalidated else { continue }
            
            resolve(element: element, toBeDeleted: &toBeDeleted)
        }
    }
    
    private func resolve(element: Object, toBeDeleted: inout Set<RLMObjectBase>) {
        element.objectSchema.properties.forEach {
            guard let value = element.value(forKey: $0.name) else { return }
            
            if let entity = value as? RLMObjectBase {
                toBeDeleted.insert(entity)
            } else if let list = value as? RLMSwiftCollectionBase {
                for index in 0..<list._rlmCollection.count {
                    if let object = list._rlmCollection.object(at: index) as? RLMObjectBase {
                        toBeDeleted.insert(object)
                    }
                }
            }
        }
        
        delete(element)
    }
}

@iSevenDays
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@cpd, thanks for letting us know! I didn't know the cascading delete was implemented. Thanks!

@lif-wtag
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@cpd, Thanks a lot mate!
I was having trouble with Resolve function as RealmSwift.ListBase is no longer supported in RealmSwift v10.17.0.
Your code with RLMSwiftCollectionBase helped me, Thanks again.

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