[Solved] You want to create a SwiftData model for a Book with a title and optional author.... Which code snippet correctly defines the model and query? | iOS Swift

iOS Swift - Local Data Persistence

You want to create a SwiftData model for a Book with a title and optional author. You also want to fetch all books with a non-empty author in a SwiftUI view. Which code snippet correctly defines the model and query?

A

<pre>@Model
class Book {
  var title: String
  var author: String
  init() { title = ""; author = "" }
}</pre>
<pre>@Query(filter: #Predicate { $0.author != "" }) var books: [Book]</pre>

B

<pre>@Model
class Book {
  var title: String = ""
  var author: String? = nil
}</pre>
<pre>@Query(filter: #Predicate { $0.author != nil && !$0.author!.isEmpty }) var books: [Book]</pre>

C

<pre>@Model
class Book {
  var title: String
  var author: String?
}</pre>
<pre>@Query(filter: #Predicate { $0.author != nil }) var books: [Book]</pre>

D

<pre>@Model
class Book {
  var title: String = ""
  var author: String = ""
}</pre>
<pre>@Query(filter: #Predicate { $0.author.isEmpty }) var books: [Book]</pre>

Step-by-Step Solution

Solution:

Step 1: Define model with optional author and default values

@Model
class Book {
  var title: String = ""
  var author: String? = nil
}

@Query(filter: #Predicate { $0.author != nil && !$0.author!.isEmpty }) var books: [Book]

correctly defines author as optional with a default nil and title with a default empty string.

Step 2: Use a filter predicate to fetch books with non-empty author
The filter checks author != nil and that author is not empty, matching the requirement.
Final Answer:
Correctly defines the model and query for non-empty authors. -> Option B

Quick Check:

Optional author + filter for non-empty =

@Model
class Book {
  var title: String = ""
  var author: String? = nil
}

@Query(filter: #Predicate { $0.author != nil && !$0.author!.isEmpty }) var books: [Book]

[OK]

Quick Trick: Use optional property and filter for non-empty string [OK]

Common Mistakes:

Forgetting to make author optional
Using empty string author without optional
Incorrect filter logic for non-empty strings

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More iOS Swift Quizzes

Which code snippet correctly defines the model and query?

Step 1: Define model with optional author and default values

Step 2: Use a filter predicate to fetch books with non-empty author

Final Answer:

Quick Check:

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