Realm: How to fix 'Invalid property name' RLMException during migration - ios

Question

My iOS app uses RealmSwift, and it is crashing during migration from an older version of the app. The error is: RLMException: Invalid Property Name <name> for class <class>.
The crash seems to be happening because of the following sequence of migrations:
Initial: Created a model (lets call it Story)
class Story: Object, Mappable {
#objc dynamic var _id = ""
#objc dynamic var lastModified: Date?
#objc dynamic var name = ""
#objc dynamic var content = ""
override static func primaryKey() -> String? {
return ServerKey.id
}
override static func indexedProperties() -> [String] {
return ["name"]
}
}
Migration X: Created another model using migration.create (lets call it Book) which contains the model created in the previous step (Book contains Story)
private class func migrateToVersionX(_ migration: Migration) {
migration.enumerateObjects( <perform unrelated migration to change some values on story objects> )
migration.create("Book", value: ["stories": <array containing stories>])
}
Migration X+2: Added a new field to Story (Story.author)
class Story: Object, Mappable {
#objc dynamic var _id = ""
#objc dynamic var lastModified: Date?
#objc dynamic var name = ""
#objc dynamic var content = ""
#objc dynamic var author = ""
override static func primaryKey() -> String? {
return ServerKey.id
}
override static func indexedProperties() -> [String] {
return ["name", "author"]
}
}
When a user has a version older than MigrationX, the app crashes with the following error (modified for this example)
'RLMException', reason: 'Invalid property name 'author' for class 'Story'.'
The app crashes at the migration.create call. This is the stack trace
Fatal Exception: RLMException
Invalid property name 'author' for class 'Story'.
0 CoreFoundation
__exceptionPreprocess
1 libobjc.A.dylib
objc_exception_throw
2 Realm
RLMAccessor.mm line 567
RLMDynamicGetByName
3 RealmSwift
Object.swift line 362
DynamicObject.subscript.getter
4 RealmSwift
<compiler-generated> line 0
#objc DynamicObject.value(forUndefinedKey:)
5 Foundation
-[NSObject(NSKeyValueCoding) valueForKey:]
6 Realm
RLMObjectBase.mm line 174
-[RLMObjectBase valueForKey:]
7 Realm
RLMObjectBase.mm line 451
RLMValidatedValueForProperty
8 Realm
RLMAccessor.mm line 633
RLMAccessorContext::propertyValue(objc_object*, unsigned long, RLMProperty*)
9 Realm
RLMAccessor.mm line 776
RLMAccessorContext::value_for_property(objc_object*,
std::__1::basic_string<char, std::__1::char_traits<char>,
std::__1::allocator<char> > const&, unsigned long)
10 Realm
object_accessor.hpp line 267
realm::Object realm::Object::create<objc_object* __strong, RLMAccessorContext>(RLMAccessorContext&, std::__1::shared_ptr<realm::Realm> const&, realm::ObjectSchema const&, objc_object* __strong, bool, realm::BasicRow<realm::Table>*)
11 Realm
row.hpp line 759
RLMCreateObjectInRealmWithValue
12 Realm
RLMAccessor.mm line 752
realm::BasicRowExpr<realm::Table> RLMAccessorContext::unbox<realm::BasicRowExpr<realm::Table> >(objc_object*, bool, bool)
13 Realm
list.hpp line 192
auto realm::List::dispatch<void realm::List::add<objc_object* __strong&, RLMAccessorContext>(RLMAccessorContext&, objc_object* __strong&&&, bool)::'lambda'(objc_object* __strong&)>(objc_object* __strong&&&) const
14 Realm
RLMAccessor.hpp line 77
void RLMAccessorContext::enumerate_list<void realm::List::assign<objc_object* __strong&, RLMAccessorContext>(RLMAccessorContext&, objc_object* __strong&&&, bool)::'lambda'(objc_object* __strong&&&)>(objc_object*, objc_object* __strong&&&)
15 Realm
list.hpp line 220
void realm::List::assign<objc_object* __strong&, RLMAccessorContext> (RLMAccessorContext&, objc_object* __strong&&&, bool)
16 Realm
object_accessor.hpp line 94
void realm::Object::set_property_value_impl<objc_object* __strong, RLMAccessorContext>(RLMAccessorContext&, realm::Property const&, objc_object* __strong, bool, bool)
17 Realm
object_accessor.hpp line 281
realm::Object realm::Object::create<objc_object* __strong, RLMAccessorContext>(RLMAccessorContext&, std::__1::shared_ptr<realm::Realm> const&, realm::ObjectSchema const&, objc_object* __strong, bool, realm::BasicRow<realm::Table>*)
18 Realm
row.hpp line 759
RLMCreateObjectInRealmWithValue
19 Realm
RLMRealm.mm line 840
-[RLMRealm createObject:withValue:]
20 Realm
RLMMigration.mm line 135
-[RLMMigration createObject:withValue:]
21 RealmSwift
Migration.swift line 129
Migration.create(_:value:)
22 Project Name
MigrationHelper.swift line 187
specialized static MigrationHelper.migrateToVersionX(_:)
I think what is happening is that the migration.create function in MigrationX is looking at the Story class and finding the author field, even though it formally isn't introduced until MigrationX+2.
Any thoughts on why this crash is happening and how to appropriately handle this scenario would be greatly appreciated.