Cloud Firestore in iOS Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Firestore module in Swift.

iOS Swift

import [1]

Drag options to blanks, or click blank then click option'

AFirebaseFirestore

BUIKit

CFoundation

DSwiftUI

Attempts:

3 left

💡 Hint

Common Mistakes

Importing UIKit or Foundation instead of FirebaseFirestore.

Forgetting to import any Firestore-related module.

You need to import FirebaseFirestore to use Firestore features in your Swift app.

2fill in blank

medium

Complete the code to get a Firestore database instance.

iOS Swift

let db = Firestore.[1]()

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Adefault

BfirestoreClient

Cshared

Dfirestore

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'shared' or 'default' which are not Firestore methods.

Trying to create a new instance instead of using the provided method.

Use Firestore.firestore() to get the default Firestore database instance.

3fill in blank

hard

Fix the error in the code to add data to a Firestore collection.

iOS Swift

db.collection("users").[1](data: ["name": "Alice", "age": 30]) { error in
  if let error = error {
    print("Error adding document: \(error)")
  } else {
    print("Document added successfully")
  }
}

Drag options to blanks, or click blank then click option'

AaddDocument

BsetData

CupdateDocument

DcreateDocument

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'setData' which requires a document reference, not a collection.

Using 'updateDocument' which updates existing documents only.

Use addDocument(data:completion:) to add a new document with data to a collection.

4fill in blank

hard

Fill both blanks to read documents from a Firestore collection and print their data.

iOS Swift

db.collection("products").[1] { querySnapshot, error in
  if let error = error {
    print("Error getting documents: \(error)")
  } else {
    for document in [2]?.documents ?? [] {
      print(document.data())
    }
  }
}

Drag options to blanks, or click blank then click option'

AgetDocuments

Bdocuments

CquerySnapshot

DaddSnapshotListener

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'addSnapshotListener' for one-time fetch.

Confusing the querySnapshot variable name.

Use getDocuments to fetch documents once, and querySnapshot holds the result.

5fill in blank

hard

Fill all three blanks to update a specific document's field in Firestore.

iOS Swift

let docRef = db.collection("orders").document([1])
docRef.[2](["status": [3]]) { error in
  if let error = error {
    print("Error updating document: \(error)")
  } else {
    print("Document successfully updated")
  }
}

Drag options to blanks, or click blank then click option'

A"order123"

BsetData

C"shipped"

DupdateData

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'setData' which overwrites the whole document.

Not quoting the document ID or string values.

Use document("order123") to get the document, updateData to update fields, and set the status to "shipped".

Practice

1. What is the main purpose of Cloud Firestore in an iOS app?

easy

A. To compile Swift code into an app

B. To design the app's user interface

C. To handle user authentication only

D. To store and sync app data in the cloud with live updates

Solution

1. Step 1: Understand Cloud Firestore's role

   Cloud Firestore is a cloud database that stores app data and syncs it live across devices.

2. Step 2: Compare options with Firestore's function

   Only To store and sync app data in the cloud with live updates describes storing and syncing data live, which matches Firestore's purpose.

3. Final Answer:

   To store and sync app data in the cloud with live updates -> Option D

4. Quick Check:

   Firestore = cloud data storage and sync [OK]

Hint: Firestore is for cloud data storage and live sync [OK]

Common Mistakes:

• Confusing Firestore with UI design tools
• Thinking Firestore only handles authentication
• Believing Firestore compiles code

2. Which Swift code snippet correctly gets a reference to a Firestore collection named "users"?

easy

A. let usersRef = Firestore.firestore().collection("users")

B. let usersRef = Firestore.collection("users")

C. let usersRef = Firestore.getCollection("users")

D. let usersRef = Firestore.firestore().get("users")

Solution

1. Step 1: Recall Firestore syntax for collection reference

   The correct way is to call Firestore.firestore() then .collection("name") to get a collection reference.

2. Step 2: Check each option's method calls

   Only let usersRef = Firestore.firestore().collection("users") uses Firestore.firestore().collection("users"), which is correct syntax.

3. Final Answer:

   let usersRef = Firestore.firestore().collection("users") -> Option A

4. Quick Check:

   Firestore.firestore().collection("name") = correct [OK]

Hint: Use Firestore.firestore().collection("name") to get collection [OK]

Common Mistakes:

• Omitting .firestore() before .collection()
• Using non-existent methods like getCollection()
• Calling get("users") instead of collection("users")

3. Given this Swift code, what will be printed if the document exists with field "name" = "Alice"?

let docRef = Firestore.firestore().collection("users").document("user123")
docRef.getDocument { document, error in
  if let document = document, document.exists {
    let name = document.data()?["name"] as? String ?? "Unknown"
    print(name)
  } else {
    print("No document")
  }
}

medium

A. Unknown

B. No document

C. Alice

D. Error

Solution

1. Step 1: Understand the getDocument completion handler

   If the document exists, it extracts the "name" field and prints it; otherwise prints "No document".

2. Step 2: Given document exists with "name" = "Alice"

   The code will print the value "Alice" from the document field.

3. Final Answer:

   Alice -> Option C

4. Quick Check:

   Document exists with name = Alice, so print Alice [OK]

Hint: If document exists, print its field value [OK]

Common Mistakes:

• Assuming print shows "No document" even if document exists
• Confusing default "Unknown" with actual field value
• Ignoring optional cast and default fallback

4. What is wrong with this Swift Firestore code snippet?

let docRef = Firestore.firestore().collection("users").document("user123")
docRef.getDocument { document, error in
  if error != nil {
    print("Error fetching document")
  }
  if let document = document, document.exists {
    print(document.data())
  }
}

medium

A. It does not handle the case when document does not exist

B. It uses wrong method getDocument instead of get()

C. It should unwrap error with if let error = error

D. It tries to print document.data() without casting

Solution

1. Step 1: Analyze error and document handling

   The code prints error if error exists, then prints data if document exists, but does nothing if document does not exist and no error.

2. Step 2: Identify missing handling for non-existing document

   There is no else clause for when document does not exist, so no message is shown in that case.

3. Final Answer:

   It does not handle the case when document does not exist -> Option A

4. Quick Check:

   Missing else for document.exists = problem [OK]

Hint: Always handle document not existing case [OK]

Common Mistakes:

• Confusing getDocument with get() method
• Not unwrapping error properly but still works
• Printing data() without casting is allowed

5. You want to listen for live updates to a Firestore collection "messages" and update your UI in SwiftUI. Which code snippet correctly sets up a listener?

hard

A. Firestore.firestore().collection("messages").getDocuments { snapshot, error in
let messages = snapshot?.documents.map { $0.data() } ?? []
self.messages = messages
}

B. Firestore.firestore().collection("messages").addSnapshotListener { snapshot, error in
guard let snapshot = snapshot else { return }
let messages = snapshot.documents.map { $0.data() }
DispatchQueue.main.async {
self.messages = messages
}
}

C. Firestore.firestore().collection("messages").document("messages").addSnapshotListener { snapshot, error in
if let snapshot = snapshot {
self.messages = snapshot.data()
}
}

D. Firestore.firestore().collection("messages").listen { snapshot, error in
self.messages = snapshot?.documents ?? []
}

Solution

1. Step 1: Identify method for live updates

   addSnapshotListener listens for real-time updates; getDocuments fetches once.

2. Step 2: Check correct usage of addSnapshotListener and UI update

   Firestore.firestore().collection("messages").addSnapshotListener { snapshot, error in guard let snapshot = snapshot else { return } let messages = snapshot.documents.map { $0.data() } DispatchQueue.main.async { self.messages = messages } } uses addSnapshotListener on collection, maps documents to data, and updates UI on main thread.

3. Step 3: Verify other options

   Firestore.firestore().collection("messages").getDocuments { snapshot, error in let messages = snapshot?.documents.map { $0.data() } ?? [] self.messages = messages } fetches once, not live. Firestore.firestore().collection("messages").document("messages").addSnapshotListener { snapshot, error in if let snapshot = snapshot { self.messages = snapshot.data() } } listens on a document named "messages" (wrong). Firestore.firestore().collection("messages").listen { snapshot, error in self.messages = snapshot?.documents ?? [] } uses non-existent listen method.

4. Final Answer:

   Firestore.firestore().collection("messages").addSnapshotListener { snapshot, error in guard let snapshot = snapshot else { return } let messages = snapshot.documents.map { $0.data() } DispatchQueue.main.async { self.messages = messages } } -> Option B

5. Quick Check:

   Use addSnapshotListener for live updates [OK]

Hint: Use addSnapshotListener for live Firestore updates [OK]

Common Mistakes:

• Using getDocuments for live updates
• Listening on wrong document instead of collection
• Using non-existent listen method