Column types and constraints in Flask - Practice Problems & Coding Challenges

Challenge - 5 Problems

📝 Syntax

intermediate

Identify the correct SQLAlchemy column type for storing large text

Which SQLAlchemy column type is best suited for storing large text data in a Flask model?

A db.String(255)

B db.Integer

C db.Boolean

D db.Text

💡 Hint

Think about which type can hold long paragraphs without a fixed length.

db.Text is used for large text fields without a length limit, unlike db.String which has a max length.

❓ component_behavior

intermediate

Effect of nullable constraint on a Flask model column

What happens if you set nullable=False on a column in a Flask SQLAlchemy model?

A The column cannot store NULL values and must have a value.

B The column can store NULL values.

C The column automatically generates unique values.

D The column is ignored during database creation.

💡 Hint

Think about whether the database allows empty or missing values in that column.

Setting nullable=False means the database requires a value; NULL is not allowed.

❓ state_output

advanced

Output of unique constraint violation in Flask SQLAlchemy

Given a Flask model with a column defined as email = db.Column(db.String(120), unique=True), what happens if you try to add two users with the same email?

Flask

user1 = User(email='[e-mail]')
db.session.add(user1)
db.session.commit()

user2 = User(email='[e-mail]')
db.session.add(user2)
db.session.commit()

A Both users are added successfully with the same email.

B The database ignores the unique constraint and stores both.

C The second commit raises an IntegrityError due to unique constraint violation.

D The second user silently overwrites the first user in the database.

💡 Hint

What does a unique constraint do when a duplicate value is inserted?

The unique constraint prevents duplicate values. The database raises an IntegrityError on violation.

🔧 Debug

advanced

Identify the error in this Flask SQLAlchemy column definition

What is wrong with this column definition?

age = db.Column(db.Integer, nullable='False')

Flask

age = db.Column(db.Integer, nullable='False')

A db.Integer is not a valid column type.

B nullable should be a boolean, not a string.

C The column name 'age' is reserved and cannot be used.

D There is no error; this code is correct.

💡 Hint

Check the data type expected for the nullable parameter.

The nullable parameter expects a boolean (True or False), not a string.

🧠 Conceptual

expert

Understanding composite primary keys in Flask SQLAlchemy

Which of the following correctly defines a composite primary key on columns user_id and order_id in a Flask SQLAlchemy model?

A

user_id = db.Column(db.Integer)
order_id = db.Column(db.Integer)
__table_args__ = (db.PrimaryKeyConstraint('user_id', 'order_id'),)

B

user_id = db.Column(db.Integer, primary_key=True)
order_id = db.Column(db.Integer, primary_key=True)

C

user_id = db.Column(db.Integer, unique=True)
order_id = db.Column(db.Integer, unique=True)

D

user_id = db.Column(db.Integer, nullable=False)
order_id = db.Column(db.Integer, nullable=False)

💡 Hint

Composite primary keys can be explicitly defined using __table_args__ with PrimaryKeyConstraint.

Defining multiple columns with primary_key=True works but is less explicit. Using __table_args__ with PrimaryKeyConstraint is the correct explicit way.