Repository pattern for data access in Flask - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a repository class for accessing user data.

Flask

class UserRepository:
    def __init__(self, db_session):
        self.db_session = [1]

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

Adb_session

Bsession

Cdatabase

Ddb

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different variable name than the constructor parameter.

Forgetting to assign the parameter to an instance variable.

The repository class stores the database session passed during initialization as db_session to use for data operations.

2fill in blank

medium

Complete the method to add a new user object to the database session.

Flask

def add_user(self, user):
    self.db_session.[1](user)

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

Aadd

Bsave

Cinsert

Dcommit

Attempts:

3 left

💡 Hint

Common Mistakes

Using commit instead of add.

Using insert which is not a session method.

To add a new object to the session in SQLAlchemy, use the add method.

3fill in blank

hard

Fix the error in the method to retrieve a user by ID using the session's query.

Flask

def get_user_by_id(self, user_id):
    return self.db_session.query(User).[1](user_id)

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

Afilter_by

Bget

Cfilter

Dfind

Attempts:

3 left

💡 Hint

Common Mistakes

Using filter_by without calling .first().

Using a non-existent method like find.

The get method fetches an object by primary key directly, which is efficient and correct here.

4fill in blank

hard

Fill both blanks to update a user's email and commit the change.

Flask

def update_user_email(self, user_id, new_email):
    user = self.db_session.query(User).get(user_id)
    user.email = [1]
    self.db_session.[2]()

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

Anew_email

Bcommit

Cflush

Demail

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning the wrong variable to user.email.

Calling flush instead of commit.

Assign the new email to the user's email attribute, then call commit to save changes.

5fill in blank

hard

Fill all three blanks to delete a user by ID and commit the transaction.

Flask

def delete_user(self, user_id):
    user = self.db_session.query(User).[1](user_id)
    if user:
        self.db_session.[2](user)
        self.db_session.[3]()

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

Aget

Bdelete

Ccommit

Dfilter_by

Attempts:

3 left

💡 Hint

Common Mistakes

Using filter_by without fetching the object.

Calling commit before deleting.

Retrieve the user by primary key with get, delete the user object, then commit the session.

Practice

1. What is the main purpose of using the Repository pattern in a Flask application?

easy

A. To create HTML templates for the frontend

B. To speed up the Flask server response time

C. To handle user authentication automatically

D. To separate data access logic from business logic

Solution

1. Step 1: Understand the role of repository pattern

   The repository pattern is designed to separate how data is accessed from how it is used in the app logic.

2. Step 2: Identify the correct purpose in Flask context

   In Flask, this means keeping database queries inside repository classes, so the rest of the app doesn't need to know database details.

3. Final Answer:

   To separate data access logic from business logic -> Option D

4. Quick Check:

   Repository pattern = separation of concerns [OK]

Hint: Repository pattern means separate data from app logic [OK]

Common Mistakes:

• Thinking it speeds up server response
• Confusing it with authentication handling
• Assuming it creates frontend templates

2. Which of the following is the correct way to define a repository class method to get all users in Flask?

easy

A. def get_all_users(): return User.query.all()

B. def get_all_users(self): return User.query.all()

C. def get_all_users(self): return User.all()

D. def get_all_users(self): return User.query.get_all()

Solution

1. Step 1: Check method signature in a class

   Repository methods inside a class must have self as the first parameter.

2. Step 2: Verify correct SQLAlchemy query syntax

   To get all records, use User.query.all(). Other options use incorrect method names or miss self.

3. Final Answer:

   def get_all_users(self): return User.query.all() -> Option B

4. Quick Check:

   Method with self + User.query.all() = correct [OK]

Hint: Repository methods need self and correct query syntax [OK]

Common Mistakes:

• Omitting self parameter in method
• Using wrong query method like User.all()
• Using User.query.get_all() which doesn't exist

3. Given this repository method in Flask:

def get_user_by_id(self, user_id):
    return User.query.filter_by(id=user_id).first()

What will repo.get_user_by_id(5) return if no user with ID 5 exists?

medium

A. None

B. Raises an exception

C. An empty list []

D. A User object with id 5

Solution

1. Step 1: Understand SQLAlchemy filter_by().first() behavior

   The first() method returns the first matching record or None if no match is found.

2. Step 2: Apply to user_id 5 with no matching user

   Since no user with ID 5 exists, the method returns None, not a list or exception.

3. Final Answer:

   None -> Option A

4. Quick Check:

   filter_by().first() returns None if no match [OK]

Hint: filter_by().first() returns None if no record found [OK]

Common Mistakes:

• Expecting an empty list instead of None
• Thinking it raises an exception
• Assuming it returns a dummy User object

4. You wrote this repository method:

def add_user(self, user):
    db.session.add(user)
    db.session.commit

What is the error here?

medium

A. Missing parentheses after commit method call

B. db.session.add should be db.add

C. user parameter should be a dictionary, not an object

D. commit should be called before add

Solution

1. Step 1: Check method calls on db.session

   The commit method must be called with parentheses: commit().

2. Step 2: Identify the missing parentheses error

   Without parentheses, commit is just a reference, so changes are not saved.

3. Final Answer:

   Missing parentheses after commit method call -> Option A

4. Quick Check:

   commit() needs parentheses to execute [OK]

Hint: Always call commit() with parentheses [OK]

Common Mistakes:

• Forgetting parentheses on commit
• Using db.add instead of db.session.add
• Calling commit before add

5. You want to implement a repository method that returns all users whose email ends with '@example.com'. Which of these is the best way to write it using SQLAlchemy in Flask?

hard

A. def get_example_users(self): return User.query.filter(User.email.contains('@example.com')).first()

B. def get_example_users(self): return User.query.filter_by(email='@example.com').all()

C. def get_example_users(self): return User.query.filter(User.email.endswith('@example.com')).all()

D. def get_example_users(self): return User.query.filter(User.email == '@example.com').all()

Solution

1. Step 1: Understand filtering by string suffix in SQLAlchemy

   To filter emails ending with a string, use filter(User.email.endswith(...)).

2. Step 2: Check each option's correctness

   def get_example_users(self): return User.query.filter(User.email.endswith('@example.com')).all() uses endswith and all() to get all matches, which is correct. def get_example_users(self): return User.query.filter_by(email='@example.com').all() uses filter_by with exact match, not suffix. def get_example_users(self): return User.query.filter(User.email.contains('@example.com')).first() uses contains but returns only first match. def get_example_users(self): return User.query.filter(User.email == '@example.com').all() uses equality check, not suffix.

3. Final Answer:

   def get_example_users(self): return User.query.filter(User.email.endswith('@example.com')).all() -> Option C

4. Quick Check:

   Use endswith() + all() for suffix filtering [OK]

Hint: Use endswith() for suffix filtering in queries [OK]

Common Mistakes:

• Using filter_by for partial matches
• Using contains but returning only first result
• Using equality operator instead of endswith