An example of the Service pattern in Swift

ExampleService.swift

import SwiftData

// Ensure the service conforms to the ObservableObject protocol
class ExampleService: ObservableObject {
  private let modelContext: ModelContext
  @Published var someList = [SomeModel]() // The published decorator for properties that should trigger SwiftUI updates
  
  // Pass the modelContext in to the initialiser so can use dependency injection during testing
  init(modelContext: ModelContext) {
    self.modelContext = modelContext
    // On init, go populate the initial someList value by fetching the records
    fetchData()
  }
  
  func someComplexMultiModelAction() {
    let someOtherRecordDescriptor = FetchDescriptor<SomeOtherModel>(sortBy: [SortDescriptor(\SomeOtherModel.created, order: .reverse)])
    do {
      if let someOtherRecord = try self.modelContext.fetch(someOtherRecordDescriptor).first {
        let someNewListItem = SomeModel(name: "New Thing", otherModelInstance: someOtherRecord)
        self.modelContext.insert(someNewListItem)
        fetchData()
      } else {
        // handle no existing Some Other Record
        let someOtherRecord = SomeOtherModel(name: "A new other record to reference")
        let someNewListItem = SomeModel(name: "New Thing", otherModelInstance: someOtherRecord)
        self.modelContext.insert(someNewListItem)
        fetchData()
      }
    } catch {
      // error handling
    }
  }
  
  func fetchData() {
    do {
      let descriptor = FetchDescriptor<SomeModel>()
       someList = try self.modelContext.fetch(descriptor)
    } catch {
       someList = []
    }
  }
}