CRUD operations with SwiftData in iOS Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

What happens when you save a new SwiftData entity?

You create a new entity instance and call modelContext.insert(newEntity) followed by try? modelContext.save(). What is the expected behavior?

iOS Swift

@Model
class Task {
  var title: String
  init(title: String) {
    self.title = title
  }
}

let newTask = Task(title: "Buy milk")
modelContext.insert(newTask)
try? modelContext.save()

A The new task is only saved in memory and lost when the app restarts.

B The new task is saved persistently and will appear in future fetches.

C The code throws a runtime error because insert is not allowed before save.

D The new task is saved but only if you call a special commit method afterwards.

💡 Hint

Think about what modelContext.save() does in SwiftData.

Calling modelContext.insert() adds the entity to the context. Then modelContext.save() writes changes to persistent storage, so the new entity is saved permanently.

📝 Syntax

intermediate

Which code correctly updates a SwiftData entity's attribute?

You have a fetched Task entity and want to update its title. Which option is correct?

iOS Swift

func updateTaskTitle(task: Task, newTitle: String) {
  // update code here
  try? modelContext.save()
}

A task.title = newTitle

B task.setValue(newTitle, forKey: "title")

C modelContext.update(task, with: ["title": newTitle])

D task.updateTitle(newTitle)

💡 Hint

SwiftData entities use property wrappers for attributes.

You update the attribute directly by assigning a new value to the property. Then saving the context persists the change.

❓ lifecycle

advanced

What happens if you delete an entity but forget to save the context?

You call modelContext.delete(entity) but do not call modelContext.save(). What is the result?

A The entity remains in persistent storage until <code>save()</code> is called.

B The app crashes with an error about unsaved changes.

C The entity is deleted from memory and persistent storage automatically.

D The entity is removed immediately from persistent storage.

💡 Hint

Think about when changes are committed to disk in SwiftData.

Deleting an entity marks it for removal in the context, but changes are only saved to disk when save() is called. Without saving, the deletion is not permanent.

❓ navigation

advanced

How to refresh a SwiftUI list after SwiftData changes?

You display a list of Task entities fetched from SwiftData. After adding a new task, the list does not update automatically. What should you do?

A Wrap the list in a <code>NavigationView</code> to enable automatic refresh.

B Manually reload the view by calling <code>setNeedsDisplay()</code> on the list.

C Use <code>@Query</code> property wrapper to fetch tasks so the list updates automatically.

D Call <code>modelContext.refreshAll()</code> after saving the new task.

💡 Hint

SwiftUI and SwiftData integration uses property wrappers for reactive updates.

The @Query property wrapper automatically fetches and updates the list when the data changes, so the UI stays in sync.

🔧 Debug

expert

Why does this SwiftData save fail with a validation error?

Given this entity definition and save code, why does saving fail?

@Model
class User {
  @Attribute(.unique) var email: String
  init(email: String) {
    self.email = email
  }
}

let user1 = User(email: "[e-mail]")
let user2 = User(email: "[e-mail]")
modelContext.insert(user1)
modelContext.insert(user2)
try modelContext.save()

A Because <code>modelContext.save()</code> requires a completion handler.

B Because you must call <code>modelContext.insert()</code> only once per context.

C Because the email property must be optional to allow duplicates.

D Because two entities have the same unique email, violating the uniqueness constraint.

💡 Hint

Look at the attribute modifiers and what they enforce.

The .unique attribute means no two entities can have the same email. Inserting two with identical emails causes a validation error on save.