Cloud Firestore CRUD in Flutter - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does CRUD stand for in Cloud Firestore?

CRUD stands for Create, Read, Update, and Delete. These are the four basic operations you can perform on data in Cloud Firestore.

beginner

How do you add a new document to a Firestore collection in Flutter?

Use the add() method on a collection reference. For example: FirebaseFirestore.instance.collection('users').add({'name': 'Anna', 'age': 25});

beginner

What method is used to read a single document from Firestore in Flutter?

Use the doc().get() method. For example: FirebaseFirestore.instance.collection('users').doc('userId').get(); This fetches the document data once.

intermediate

How do you update a document in Firestore without overwriting the entire document?

Use the update() method on a document reference. It changes only the specified fields. Example: docRef.update({'age': 30});

intermediate

What happens if you try to delete a document that does not exist in Firestore?

Deleting a non-existing document does not cause an error. Firestore treats it as a successful operation because the document is effectively gone.

Which Firestore method adds a new document with an auto-generated ID?

A add()

B set()

C update()

D get()

The add() method adds a new document with a unique ID automatically generated by Firestore.

How do you read all documents from a Firestore collection in Flutter?

A doc().get()

B collection().get()

C collection().add()

D doc().update()

Use collection().get() to fetch all documents in a collection at once.

Which method updates only specific fields of a Firestore document?

A set() with merge: true

B add()

C get()

D update()

The update() method changes only the fields you specify without overwriting the whole document.

What does the set() method do if the document already exists?

A Overwrites the entire document by default

B Creates a new document with a new ID

C Deletes the document

D Updates only specified fields

By default, set() replaces the whole document unless you use merge: true.

What is the correct way to delete a document in Firestore using Flutter?

A collection().delete()

B set() with empty data

C doc().delete()

D update() with null values

Use doc().delete() to remove a specific document from Firestore.

Explain the four CRUD operations in Cloud Firestore and how you perform each in Flutter.

Think about how you add, read, change, and remove data in Firestore.

Describe the difference between set() and update() methods in Firestore when modifying documents.

Consider what happens to the document data after each method.

Practice

1.

What does CRUD stand for in Cloud Firestore operations?

easy

A. Connect, Refresh, Upload, Delete

B. Copy, Run, Undo, Download

C. Create, Read, Update, Delete

D. Create, Remove, Update, Download

Solution

1. Step 1: Understand CRUD acronym meaning

   CRUD is a common term in databases meaning the four basic operations on data.

2. Step 2: Match each letter to the correct operation

   C = Create, R = Read, U = Update, D = Delete are the standard meanings.

3. Final Answer:

   Create, Read, Update, Delete -> Option C

4. Quick Check:

   CRUD = Create, Read, Update, Delete [OK]

Hint: Remember CRUD as basic data actions: create, read, update, delete [OK]

Common Mistakes:

• Confusing CRUD letters with unrelated words
• Mixing up 'Remove' with 'Delete'
• Thinking CRUD includes 'Download'

2.

Which Flutter code snippet correctly adds a new document to a Firestore collection named users?

FirebaseFirestore.instance.collection('users').____({'name': 'Alice'});

easy

A. update

B. add

C. delete

D. get

Solution

1. Step 1: Identify method to add new document

   The add method creates a new document with given data in the collection.

2. Step 2: Confirm other methods' purposes

   update modifies existing documents, delete removes documents, get reads data.

3. Final Answer:

   add -> Option B

4. Quick Check:

   Adding new document uses add() [OK]

Hint: Use add() to create new documents in a collection [OK]

Common Mistakes:

• Using update() to add new documents
• Confusing get() with add()
• Trying to delete() when adding data

3.

What will be the output of this Flutter Firestore code snippet?

var doc = await FirebaseFirestore.instance.collection('tasks').doc('task1').get();
print(doc.exists);

Assuming the document task1 exists in the tasks collection.

medium

A. true

B. false

C. null

D. Throws an error

Solution

1. Step 1: Understand doc.get() behavior

   The get() method fetches the document snapshot from Firestore.

2. Step 2: Check the exists property

   If the document exists, doc.exists returns true; otherwise false.

3. Final Answer:

   true -> Option A

4. Quick Check:

   Document exists property = true [OK]

Hint: doc.exists is true if document is found in Firestore [OK]

Common Mistakes:

• Assuming doc.exists returns document data
• Expecting false even if document exists
• Not awaiting the get() call

4.

Identify the error in this Flutter Firestore update code:

FirebaseFirestore.instance.collection('users').doc('user1').update({'age': 30});

Assuming the document user1 does not exist.

medium

A. No error, update creates document if missing

B. Update silently fails without error

C. Syntax error in update method call

D. Throws an error because document does not exist

Solution

1. Step 1: Understand update() behavior on missing document

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

2. Step 2: Confirm no syntax errors

   The syntax is correct, so error is due to missing document.

3. Final Answer:

   Throws an error because document does not exist -> Option D

4. Quick Check:

   update() fails if document missing [OK]

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

Common Mistakes:

• Thinking update() creates new documents
• Confusing update() with set()
• Ignoring async/await for update()

5.

You want to delete a Firestore document only if it exists to avoid errors. Which Flutter code snippet correctly does this?

var docRef = FirebaseFirestore.instance.collection('orders').doc('order1');
// What code to safely delete?

hard

A. docRef.get().then((doc) { if (doc.exists) docRef.delete(); });

B. docRef.delete();

C. docRef.update({'deleted': true});

D. docRef.set(null);

Solution

1. Step 1: Check document existence before deleting

   Use get() to fetch the document snapshot and check exists.

2. Step 2: Call delete() only if document exists

   This avoids errors from deleting non-existing documents.

3. Final Answer:

   docRef.get().then((doc) { if (doc.exists) docRef.delete(); }); -> Option A

4. Quick Check:

   Check exists before delete to avoid errors [OK]

Hint: Always check doc.exists before delete() to prevent errors [OK]

Common Mistakes:

• Calling delete() without checking existence
• Using update() to delete documents
• Setting document to null instead of deleting