Deleting Classes in List<T> during Realm Migration - realm-list

Question

For example. I have old models, like this:
class Foo:Object {
#objc dynamic var id = ObjectId.generate()
let bars = List<Bar>()
override class func primaryKey() -> String? {
return "id"
}
}
class Bar:Object {
#objc dynamic var id = ObjectId.generate()
override class func primaryKey() -> String? {
return "id"
}
}
and the new models:
class Foo:Object {
#objc dynamic var id = ObjectId.generate()
override class func primaryKey() -> String? {
return "id"
}
}
migration code:
let config = Realm.Configuration(
schemaVersion: 1,
migrationBlock: {migration, oldSchemaVersion in
if oldSchemaVersion < 1 {
migration.deleteData(forType: "Bar")
}
})
let realm = try! Realm(configuration: config)
When running, the error shows "Table is target of cross-table link columns".
If I ran first
let config = Realm.Configuration(
schemaVersion: 1,
migrationBlock: {migration, oldSchemaVersion in
if oldSchemaVersion < 1 {
}
})
and then ran
let config = Realm.Configuration(
schemaVersion: 2,
migrationBlock: {migration, oldSchemaVersion in
if oldSchemaVersion < 1 {
}
if oldSchemaVersion < 2 {
migration.deleteData(forType: "Bar")
}
})
The result worked.
Here is the question, is that a way to merge the two times migrations into one migration?

Answer 1

I found a solution. Just apply the two migrations together.
let url = Realm.Configuration().fileURL!
let schemaVersion = try! schemaVersionAtURL(url)
if schemaVersion == 0 {
autoreleasepool {
let configuration = Realm.Configuration(
// Set the new schema version. This must be greater than the previously used
// version (if you've never set a schema version before, the version is 0).
schemaVersion: 1,
migrationBlock: { migration, oldSchemaVersion in
// We haven’t migrated anything yet, so oldSchemaVersion == 0
if (oldSchemaVersion < 1) {
}
})
_ = try! Realm(configuration: configuration)
}
autoreleasepool {
let configuration = Realm.Configuration(
// Set the new schema version. This must be greater than the previously used
// version (if you've never set a schema version before, the version is 0).
schemaVersion: 2,
migrationBlock: { migration, oldSchemaVersion in
// We haven’t migrated anything yet, so oldSchemaVersion == 0
if (oldSchemaVersion < 1) {
}
if (oldSchemaVersion < 2) {
migration.deleteData(forType: "Bar")
}
})
_ = try! Realm(configuration: configuration)
}
} else {
let configuration = Realm.Configuration(schemaVersion: schemaVersion)
_ = try! Realm(configuration: configuration)
}
The autoreleasepool parts are necessary. Or schemaVersion 2 won't be applied.