Updating specific fields in Firebase - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to update a single field in a Firestore document.

Firebase

db.collection('users').doc('user123').update({ 'age': [1] });

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

A30

B'30'

Cage

Dupdate

Attempts:

3 left

💡 Hint

Common Mistakes

Putting the number in quotes, making it a string.

Using the field name instead of the value.

The value to update the field must be a number, not a string or a variable name.

2fill in blank

medium

Complete the code to update the 'status' field to 'active' in a Firestore document.

Firebase

db.collection('tasks').doc('task1').update({ 'status': [1] });

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

Aactive

B'active'

C"active"

Dstatus

Attempts:

3 left

💡 Hint

Common Mistakes

Not using quotes around the string value.

Using the field name instead of the value.

String values in JavaScript must be inside quotes.

3fill in blank

hard

Fix the error in the code to update the 'email' field in Firestore.

Firebase

db.collection('users').doc('user456').update({ email: [1] });

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

Auser.email

B"[e-mail]"

CuserEmail

D'[e-mail]'

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable name without defining it.

Not using quotes around the email string.

The email value must be a string literal with quotes.

4fill in blank

hard

Fill both blanks to update 'firstName' and 'lastName' fields in Firestore.

Firebase

db.collection('users').doc('user789').update({ 'firstName': [1], 'lastName': [2] });

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

A'John'

B'Doe'

CJohn

DDoe

Attempts:

3 left

💡 Hint

Common Mistakes

Not using quotes around the names.

Using unquoted variable names.

Both names must be strings with quotes.

5fill in blank

hard

Fill all three blanks to update 'city', 'state', and 'zip' fields in Firestore.

Firebase

db.collection('addresses').doc('addr1').update({ 'city': [1], 'state': [2], 'zip': [3] });

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

A'Seattle'

B'WA'

C98101

D9810

Attempts:

3 left

💡 Hint

Common Mistakes

Putting zip code in quotes making it a string.

Not quoting city or state strings.

City and state are strings with quotes; zip is a number without quotes.

Practice

1. What does the update() method do in Firebase Firestore?

easy

A. It creates a new collection in Firestore.

B. It deletes the entire document from the collection.

C. It changes only specific fields in a document without overwriting the whole document.

D. It reads all documents in a collection.

Solution

1. Step 1: Understand the purpose of update()

   The update() method modifies only the fields you specify in an existing document.

2. Step 2: Compare with other methods

   Unlike set(), update() does not overwrite the entire document, preserving other fields.

3. Final Answer:

   It changes only specific fields in a document without overwriting the whole document. -> Option C

4. Quick Check:

   update() modifies specific fields only [OK]

Hint: update() changes fields without replacing the whole document [OK]

Common Mistakes:

• Thinking update() deletes documents
• Confusing update() with set() creating collections
• Believing update() reads data

2. Which of the following is the correct syntax to update the field age to 30 in a Firestore document reference docRef?

easy

A. docRef.update({ age: 30 });

B. docRef.set({ age: 30 });

C. docRef.update(age = 30);

D. docRef.modify({ age: 30 });

Solution

1. Step 1: Identify the correct method for updating fields

   The update() method is used to change specific fields without overwriting the document.

2. Step 2: Check syntax correctness

   The correct syntax is docRef.update({ age: 30 }); where the fields to update are passed as an object.

3. Final Answer:

   docRef.update({ age: 30 }); -> Option A

4. Quick Check:

   update() uses object with fields [OK]

Hint: Use update() with an object to change fields [OK]

Common Mistakes:

• Using set() which overwrites the document
• Using invalid syntax like update(age = 30)
• Using non-existent method modify()

3. Given this code snippet:

const docRef = firestore.collection('users').doc('user123');
docRef.update({ 'profile.name': 'Alice', 'profile.age': 28 });

What will happen if the document user123 does not exist?

medium

A. The update will fail with an error because the document does not exist.

B. The update will silently do nothing and return success.

C. The update will create the document with the specified fields.

D. The update will overwrite the entire document with the new fields.

Solution

1. Step 1: Understand update() behavior on non-existing documents

   The update() method requires the document to exist; otherwise, it throws an error.

2. Step 2: Analyze the code context

   Since user123 does not exist, the update call will fail with an error.

3. Final Answer:

   The update will fail with an error because the document does not exist. -> Option A

4. Quick Check:

   update() fails if document missing [OK]

Hint: update() needs existing document; else error occurs [OK]

Common Mistakes:

• Assuming update() creates documents
• Thinking update() silently succeeds
• Confusing update() with set() with merge

4. You try to update a nested field using this code:

docRef.update({ 'address.city': 'New York' });

But you get an error. What is the most likely cause?

medium

A. Dot notation is not supported for nested fields in update().

B. The document does not exist, so update() fails.

C. You must use set() instead of update() for nested fields.

D. The field name 'address.city' is invalid in Firestore.

Solution

1. Step 1: Recall update() requirements

   update() requires the document to exist; otherwise, it throws an error.

2. Step 2: Check dot notation support

   Dot notation is supported for nested fields in update(), so that is not the cause.

3. Step 3: Confirm field name validity

   Field names with dot notation are valid in Firestore for nested updates.

4. Final Answer:

   The document does not exist, so update() fails. -> Option B

5. Quick Check:

   update() fails if document missing, dot notation allowed [OK]

Hint: update() fails if document missing; dot notation is valid [OK]

Common Mistakes:

• Believing dot notation is unsupported
• Thinking set() is required for nested fields
• Assuming field names with dots are invalid

5. You want to update the nested field settings.notifications.email to false in a Firestore document. The document may or may not exist. Which code snippet correctly updates or creates the document without overwriting other fields?

hard

A. docRef.update({ 'settings.notifications.email': false });

B. docRef.set({ 'settings.notifications.email': false });

C. docRef.update({ settings: { notifications: { email: false } } });

D. docRef.set({ 'settings.notifications.email': false }, { merge: true });

Solution

1. Step 1: Understand update() vs set() with merge

   update() fails if the document does not exist. set() with { merge: true } creates or updates without overwriting.

2. Step 2: Analyze each option

   docRef.update({ 'settings.notifications.email': false }); fails if document missing. docRef.set({ 'settings.notifications.email': false }); overwrites entire document. docRef.set({ 'settings.notifications.email': false }, { merge: true }); correctly merges nested field. docRef.update({ settings: { notifications: { email: false } } }); incorrectly uses update() with nested object, which overwrites nested fields.

3. Final Answer:

   docRef.set({ 'settings.notifications.email': false }, { merge: true }); -> Option D

4. Quick Check:

   Use set() with merge:true to update or create safely [OK]

Hint: Use set() with merge:true to update nested fields safely [OK]

Common Mistakes:

• Using update() when document may not exist
• Using set() without merge, overwriting data
• Passing nested objects to update() causing overwrite