Adding documents (add vs set) in Firebase - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add a new document to the collection using Firestore's add method.

Firebase

db.collection('users').[1]({ name: 'Alice', age: 30 });

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

Aget

Bset

Cupdate

Dadd

Attempts:

3 left

💡 Hint

Common Mistakes

Using set instead of add when you want Firestore to generate the document ID.

Using update which requires an existing document.

The add method adds a new document with a generated ID to the collection.

2fill in blank

medium

Complete the code to set data for a document with a specific ID using Firestore's set method.

Firebase

db.collection('users').doc('user123').[1]({ name: 'Bob', age: 25 });

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

Aset

Badd

Cupdate

Ddelete

Attempts:

3 left

💡 Hint

Common Mistakes

Using add which does not allow specifying the document ID.

Using update which fails if the document does not exist.

The set method writes data to a document with the specified ID, creating it if it doesn't exist.

3fill in blank

hard

Fix the error in the code to correctly add a document with generated ID.

Firebase

db.collection('orders').doc().[1]({ item: 'Book', quantity: 2 });

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

Aupdate

Badd

Cset

Dget

Attempts:

3 left

💡 Hint

Common Mistakes

Using add on a document reference instead of a collection.

Using update on a non-existing document.

When using doc() without arguments, you get a reference to a new document ID. To add data, use set on that document reference.

4fill in blank

hard

Fill both blanks to create a new document with a generated ID and set data in one step.

Firebase

db.collection('products').[1]([2]);

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

Aadd

B{ name: 'Laptop', price: 1200 }

Cset

D{ id: 'prod1', name: 'Laptop' }

Attempts:

3 left

💡 Hint

Common Mistakes

Using set without specifying a document reference.

Passing an object with an id field to add.

The add method takes an object with data to create a new document with a generated ID.

5fill in blank

hard

Fill all three blanks to set data on a document with a specific ID and merge it with existing data.

Firebase

db.collection('customers').doc([1]).[2]([3], { merge: true });

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

A'cust123'

Bset

C{ phone: '123-456-7890' }

Dadd

Attempts:

3 left

💡 Hint

Common Mistakes

Using add instead of set when specifying a document ID.

Not using merge option and overwriting existing data.

Use doc('cust123') to specify the document, set to write data, and pass the data object with { merge: true } to merge with existing data.

Practice

1. What is the main difference between add and set when adding documents in Firebase?

easy

A. add creates a document with an automatic unique ID, set uses a specified ID.

B. add updates existing documents, set only creates new documents.

C. add deletes documents, set reads documents.

D. add requires a document ID, set generates one automatically.

Solution

1. Step 1: Understand add behavior

   add creates a new document with a unique ID generated by Firebase automatically.

2. Step 2: Understand set behavior

   set creates or updates a document at a specified ID you provide.

3. Final Answer:

   add creates a document with an automatic unique ID, set uses a specified ID. -> Option A

4. Quick Check:

   add auto ID, set specified ID = A [OK]

Hint: Remember: add auto-generates ID, set needs your ID [OK]

Common Mistakes:

• Thinking set always creates new documents only
• Confusing which method generates IDs automatically
• Assuming add can update existing documents

2. Which of the following is the correct syntax to add a new document with an automatic ID in Firebase Firestore?

easy

A. db.collection('users').add({name: 'Alice'})

B. db.collection('users').set({name: 'Alice'})

C. db.collection('users').doc('user1').add({name: 'Alice'})

D. db.collection('users').doc().add({name: 'Alice'})

Solution

1. Step 1: Identify method for automatic ID

   add creates a new document with an automatic ID inside a collection.

2. Step 2: Check syntax correctness

   db.collection('users').add({name: 'Alice'}) is the correct syntax to add a new document with auto ID.

3. Final Answer:

   db.collection('users').add({name: 'Alice'}) -> Option A

4. Quick Check:

   Use add for auto ID = B [OK]

Hint: Use add() on collection to auto-generate document ID [OK]

Common Mistakes:

• Using set() without specifying a document ID
• Calling add() on a document reference instead of collection
• Using doc() without an ID then calling add()

3. What will be the result of this code snippet?

db.collection('products').doc('p1').set({name: 'Book', price: 10});
db.collection('products').doc('p1').set({price: 12});

medium

A. The document 'p1' will have {name: 'Book', price: 12}

B. The document 'p1' will have {name: 'Book', price: 10, price: 12}

C. The document 'p1' will have only {price: 12}, name is removed

D. An error occurs because set is called twice

Solution

1. Step 1: Analyze first set call

   The first set creates or overwrites document 'p1' with {name: 'Book', price: 10}.

2. Step 2: Analyze second set call without merge

   The second set overwrites the entire document with {price: 12}, removing 'name' because merge option is not used.

3. Final Answer:

   The document 'p1' will have only {price: 12}, name is removed -> Option C

4. Quick Check:

   set without merge overwrites whole document = C [OK]

Hint: set without merge replaces whole document, removing old fields [OK]

Common Mistakes:

• Assuming set merges fields by default
• Expecting both name and price to remain
• Thinking calling set twice causes error

4. Identify the error in this code snippet and how to fix it:

db.collection('orders').add({id: 'order1', total: 50});
db.collection('orders').doc('order1').set({total: 60});

medium

A. No error; both lines work fine together.

B. The first line creates a document with a random ID, so the second line updates a different document.

C. The second line should use add() instead of set().

D. The first line should specify the document ID using doc('order1').set() instead of add().

Solution

1. Step 1: Understand add() behavior

   The first line adds a document with a random ID, ignoring the 'id' field inside data.

2. Step 2: Understand doc('order1').set() behavior

   The second line sets data on a document with ID 'order1', which is different from the random ID created before.

3. Step 3: Identify mismatch

   Because IDs differ, the second line updates a different document than the one created by add().

4. Final Answer:

   The first line creates a document with a random ID, so the second line updates a different document. -> Option B

5. Quick Check:

   add() random ID ≠ doc('order1') ID = A [OK]

Hint: add() ignores id field; doc(id).set() targets specific document [OK]

Common Mistakes:

• Assuming add() uses the id field as document ID
• Using set() on a doc without knowing if it exists
• Expecting add() and set() to affect same document automatically

5. You want to update only the 'price' field of a document without removing other fields. Which Firebase method and option should you use?

hard

A. Use add() with the new price data.

B. Use set() without any options.

C. Use update() without any options.

D. Use set() with {merge: true} option.

Solution

1. Step 1: Understand add() behavior

   add() creates a new document with a random ID; it cannot update existing documents.

2. Step 2: Understand set() without merge

   set() without options overwrites the whole document, removing other fields.

3. Step 3: Understand set() with merge option

   set() with {merge: true} updates only specified fields, keeping others intact.

4. Step 4: Consider update()

   update() also updates fields but requires the document to exist; set() with merge works even if document is new.

5. Final Answer:

   Use set() with {merge: true} option. -> Option D

6. Quick Check:

   Partial update without overwrite = set() + merge true = D [OK]

Hint: Use set() with merge:true to update fields without deleting others [OK]

Common Mistakes:

• Using add() to update existing documents
• Using set() without merge and losing data
• Confusing update() with set() merge behavior