Cascading deletion for RealmSwift

Realm+CascadeDeleting.swift

import Foundation
import RealmSwift
import Realm

//Forked from: https://gist.github.com/krodak/b47ea81b3ae25ca2f10c27476bed450c

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 RLMListBase:
                for index in 0 ..< list._rlmArray.count {
                    guard let realmObject = list._rlmArray.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) }
                }
            }
        }
    }
}

Perhaps you have an error in the filtering block:

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

You are trying to apply a filter to CascadingDeletable.Type, but the type does not have the propertiesToCascadeDelete property, it might be more correct to do this using object.

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

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

Note the static on the protocol requirement. It's a var on the type not the instance. I don't think your example would compile.

Please feel free to test the version with replaced RLMListBase

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) }
				}
			}
		}
	}
}