Transaction basics in Firebase - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start a transaction in Firebase.

Firebase

db.runTransaction([1]);

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AupdateData

BtransactionFunction

CcommitTransaction

DstartTransaction

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a string instead of a function.

Using method names that do not exist on the database object.

The runTransaction method requires a function that defines the transaction operations. This function is passed as an argument.

2fill in blank

medium

Complete the code to get a document reference inside a transaction.

Firebase

const docRef = db.collection('users').doc([1]);

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ArefId

Btransaction

CdocData

DuserId

Attempts:

3 left

💡 Hint

Common Mistakes

Using the transaction object instead of the document ID.

Passing undefined or wrong variable names.

The doc() method requires the document ID, which is usually stored in a variable like userId.

3fill in blank

hard

Fix the error in reading data inside the transaction function.

Firebase

return transaction.get(docRef).then(doc => {
  if (!doc.exists) {
    throw new Error('Document does not exist');
  }
  const newCount = doc.data().count [1] 1;
  transaction.update(docRef, { count: newCount });
});

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A+

B+=

C-

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using += inside an expression causes syntax errors.

Using subtraction or multiplication instead of addition.

To increase the count by 1, use the + operator. The += operator cannot be used inside expressions like this.

4fill in blank

hard

Fill both blanks to correctly update a field and commit the transaction.

Firebase

transaction.[1](docRef, { [2]: newValue });

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Aupdate

Bset

Ccount

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using set which replaces the whole document.

Using incorrect field names.

The update method changes specific fields. Here, the field count is updated with newValue.

5fill in blank

hard

Fill all three blanks to complete the transaction function that increments a user's score.

Firebase

db.runTransaction(async (transaction) => {
  const docRef = db.collection('users').doc([1]);
  const doc = await transaction.get(docRef);
  if (!doc.exists) {
    throw new Error('User not found');
  }
  const newScore = doc.data().[2] [3] 1;
  transaction.update(docRef, { score: newScore });
});

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

AuserId

Bscore

C+

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong variable names for document ID or field.

Using incorrect operators like - or *.

The document ID is userId. The field to increment is score, and the operator to add 1 is +.