Currently, my Realm database contains a plain array of MyData objects:
class MyData: Object {
@objc dynamic var name = ""
@objc dynamic var age = 0
}
For instance, it may contain
[
["Alice", 12],
["Bob", 13],
["Alice", 22],
["Carolina", 13],
["Bob", 20]
]
I am going to rework it so that to make name unique keeping the biggest age:
[
["Alice", 22],
["Bob", 20],
["Carolina", 13]
]
also, I want to make name a primary key to avoid duplication in future.
So I changed class description as
class MyData: Object {
@objc dynamic var name = ""
@objc dynamic var age = 0
override static func primaryKey() -> String? {
return "name"
}
}
And now I need to provide a migration block:
let config = Realm.Configuration(
schemaVersion: 1,
migrationBlock: { migration, oldSchemaVersion in
switch oldSchemaVersion {
case 0:
migration.enumerateObjects(ofType: MyData.className()) { (oldObject, newObject) in
// how to do it?
}
default:
break
}
})
I do not understand what to do in enumeration block. In my example, I have five "old" objects (without primary key), and I will have three "new" objects (with primary key), so how do I do this transformation?
Did you just try to increment schema version and add property deleteRealmIfMigrationNeeded to true ?
Realm.Configuration.defaultConfiguration = Realm.Configuration(
schemaVersion: 2,
migrationBlock: { migration, oldSchemaVersion in },
deleteRealmIfMigrationNeeded: true
)
EDIT:
Sorry, it's not true because you need to keep only oldest people so try use delete method of realm migration object:
let config = Realm.Configuration(
schemaVersion: 1,
migrationBlock: { migration, oldSchemaVersion in
switch oldSchemaVersion {
case 0:
var objects: [String: Any] = []
migration.enumerateObjects(ofType: MyData.className()) {
(oldObject, newObject) in
if let age = oldObject["age"] as? Int, age > objects[oldObject["name"]] {
migration.delete(oldObject["name"])
objects[oldObject["name"]] = oldObject
} else {
migration.delete(oldObject)
}
}
default:
break
}
})