# init(fetchDescriptor:sectionBy:modelContainer:isolation:) Creates a new observer with the given fetch descriptor, an optional String section key path, and a model container. ``` convenience init(fetchDescriptor: FetchDescriptor = FetchDescriptor(), sectionBy: KeyPath, modelContainer: ModelContainer, isolation: isolated (any Actor)? = #isolation) throws ``` ## Parameters `fetchDescriptor` The descriptor defining the fetch criteria. `sectionBy` A key path on the element type that returns an optional section name. `modelContainer` The model container from which a new context will be created. ## Discussion> Throws: An error if the initial fetch fails. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)