CRUD operations with SwiftData in iOS Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does CRUD stand for in app development?

CRUD stands for Create, Read, Update, and Delete. These are the four basic operations to manage data in an app.

beginner

How do you create a new object in SwiftData?

You create a new object by initializing your model and then saving the context. For example, use @Model to define data and then call context.insert(newObject) followed by context.save().

beginner

How do you fetch data using SwiftData?

Use a @Query property wrapper to fetch data. It automatically keeps your UI updated when data changes. For example, @Query var items: [Item] fetches all Item objects.

intermediate

How do you update an existing object in SwiftData?

To update, change the properties of the fetched object and then save the context. SwiftData tracks changes automatically, so just call context.save() after editing.

beginner

What is the correct way to delete an object in SwiftData?

Call context.delete(object) on the object you want to remove, then save the context with context.save(). This removes the object from the database.

Which SwiftData property wrapper is used to fetch data reactively?

A @Query

B @State

C @Published

D @ObservedObject

@Query fetches data from SwiftData and updates the UI automatically when data changes.

What must you do after creating or modifying data in SwiftData to save changes?

A Call context.save()

B Restart the app

C Call context.fetch()

D Nothing, changes save automatically

You must call context.save() to persist changes to the database.

How do you delete an object from SwiftData?

A Set object to nil

B Remove the object from an array

C context.delete(object) then context.save()

D Call object.remove()

Deleting requires calling context.delete(object) and then saving the context.

Which CRUD operation involves changing properties of an existing object?

A Delete

B Create

C Read

D Update

Update means modifying existing data.

What is the purpose of the @Model attribute in SwiftData?

A Fetches data from the database

B Defines a data model class

C Deletes data

D Updates UI state

@Model marks a class or struct as a data model for SwiftData.

Explain the steps to create and save a new data object using SwiftData.

Think about how you add a new item to a list and save it.

Describe how SwiftData helps keep your app UI updated when data changes.

Imagine your app list changes automatically when you add or remove items.

Practice

1. What does the @Model attribute in SwiftData represent?

easy

A. A UI component for displaying lists

B. A data model class used to define entities for CRUD operations

C. A function to fetch data from the network

D. A SwiftUI view modifier for styling

Solution

1. Step 1: Understand the role of @Model

   The @Model attribute marks a class as a data model entity for SwiftData, enabling CRUD operations.

2. Step 2: Differentiate from UI and functions

   It is not related to UI components, network functions, or view modifiers.

3. Final Answer:

   A data model class used to define entities for CRUD operations -> Option B

4. Quick Check:

   @Model defines data entities = B [OK]

Hint: Remember @Model marks data classes, not UI or functions [OK]

Common Mistakes:

• Confusing @Model with UI components
• Thinking @Model fetches data
• Mixing @Model with view modifiers

2. Which of the following is the correct way to declare a SwiftData model class named Book with a title property of type String?

easy

A. @Model class Book { var title: String }

B. @Model struct Book { var title: String }

C. struct Book { var title: String }

D. class Book: ObservableObject { var title: String }

Solution

1. Step 1: Identify correct @Model usage

   SwiftData requires @Model on a class, not a struct, to define a data entity.

2. Step 2: Check class vs struct and attribute

   @Model class Book { var title: String } correctly uses @Model with a class and a property.

3. Final Answer:

   @Model class Book { var title: String } -> Option A

4. Quick Check:

   @Model + class + properties = D [OK]

Hint: Use @Model with class, not struct, for SwiftData models [OK]

Common Mistakes:

• Using struct instead of class for @Model
• Omitting @Model attribute
• Using ObservableObject instead of @Model

3. Given the following SwiftData code snippet, what will be the output when printing books.count after adding a new book?

struct ContentView: View {
  @Environment(\"modelContext\") private var modelContext
  @Query var books: [Book]

  var body: some View {
    Button(\"Add Book\") {
      let newBook = Book(title: \"SwiftData Basics\")
      modelContext.insert(newBook)
    }
    Text(\"Books count: \(books.count)\")
  }
}

medium

A. Books count: 0

B. Books count: 2

C. Books count: 1

D. Compilation error

Solution

1. Step 1: Understand @Query and modelContext.insert

   The @Query property fetches all Book entities. Inserting a new Book updates the data source.

2. Step 2: Check the effect of insertion on books.count

   After inserting one new Book, the count increases by 1, so it will be 1.

3. Final Answer:

   Books count: 1 -> Option C

4. Quick Check:

   Insert one book, count updates to 1 [OK]

Hint: Inserting updates @Query results immediately [OK]

Common Mistakes:

• Assuming count stays 0 after insert
• Expecting count to be 2 without adding twice
• Thinking code causes compile error

4. Identify the error in this SwiftData update code snippet:

func updateBookTitle(book: Book, newTitle: String) {
  book.title = newTitle
  modelContext.save()
}

medium

A. No error; code updates title correctly

B. Missing call to modelContext.insert(book)

C. book.title cannot be changed directly; must create new Book

D. modelContext.save() is not a valid method in SwiftData

Solution

1. Step 1: Check SwiftData update pattern

   In SwiftData, changes to model object properties are tracked automatically, but modelContext.save() is not a valid method to persist changes explicitly.

2. Step 2: Identify if there's an error

   Directly mutating book.title is correct, but calling modelContext.save() causes an error because the method does not exist.

3. Final Answer:

   modelContext.save() is not a valid method in SwiftData -> Option D

4. Quick Check:

   Property change tracked automatically; no save() method = A [OK]

Hint: SwiftData tracks changes automatically; no save() method needed [OK]

Common Mistakes:

• Thinking modelContext.save() exists
• Believing properties are immutable
• Confusing update with insert

5. You want to delete all Book objects with an empty title using SwiftData. Which code snippet correctly performs this operation?

hard

A. books.filter { $0.title.isEmpty }.forEach { modelContext.delete($0) }

B. for book in books where book.title.isEmpty { modelContext.delete(book) }

C. modelContext.deleteAll(Book.self, where: \"title == ''\")

D. modelContext.remove(books.filter { $0.title.isEmpty })

Solution

1. Step 1: Understand deletion in SwiftData

   To delete objects, you call modelContext.delete(object) for each object.

2. Step 2: Check each option for correctness

   books.filter { $0.title.isEmpty }.forEach { modelContext.delete($0) } filters books with empty titles and deletes each correctly. for book in books where book.title.isEmpty { modelContext.delete(book) } syntax is invalid in Swift. modelContext.deleteAll(Book.self, where: \"title == ''\") uses a non-existent method. modelContext.remove(books.filter { $0.title.isEmpty }) uses wrong method name.

3. Final Answer:

   books.filter { $0.title.isEmpty }.forEach { modelContext.delete($0) } -> Option A

4. Quick Check:

   Filter then delete each = A [OK]

Hint: Filter then delete each object individually [OK]

Common Mistakes:

• Using invalid for-in with where clause
• Calling non-existent deleteAll method
• Using wrong method name like remove