I was load testing my app that lists some todos and essentially pre-populated database with 1000 records. This slowed things down in the app dramatically, tab switching felt sluggish and I pinpointed it down to using

@Query var todos: [Todo]

However if I replace this query with a computed property that uses FetchDescriptor i.e.

var todos: [Todo] {
    var descriptor = FetchDescriptor<Todo>()
    do { return try DatabaseContainer.mainContext.fetch(descriptor) }
    catch { return [] }
}

Everything is suddenly super fast (albeit observable nature of query is lost). Why is there such a drastic performance difference?

@Query – takes ~2-3s to resolve

FetchDescriptor – is instant

Is this a known limitation / bug in SwiftData?