Relationships (one-to-many) in Flask - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a one-to-many relationship in Flask-SQLAlchemy.

Flask

class Parent(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    children = db.relationship('[1]', backref='parent')

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

AParent

Bchild

Cchildren

DChild

Attempts:

3 left

💡 Hint

Common Mistakes

Using the lowercase or plural form instead of the class name.

Using the current class name instead of the related class.

The db.relationship function takes the name of the related model class as a string. Here, the child model is named Child.

2fill in blank

medium

Complete the code to define the foreign key in the child model.

Flask

class Child(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    parent_id = db.Column(db.Integer, db.ForeignKey('[1]'))

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

Aparent.id

Bparent_id

CParent.id

Dchild.id

Attempts:

3 left

💡 Hint

Common Mistakes

Using the class name with a dot instead of the table name.

Using the column name alone without the table name.

The foreign key references the parent table and column as a string in the format tablename.columnname. The table name is usually lowercase, so parent.id is correct.

3fill in blank

hard

Fix the error in the relationship definition to enable lazy loading.

Flask

class Parent(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    children = db.relationship('Child', [1]='dynamic')

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

Alazy

Bbackref

Cforeign_key

Duselist

Attempts:

3 left

💡 Hint

Common Mistakes

Using backref or foreign_key instead of lazy.

Misspelling the parameter name.

The lazy parameter controls how related items are loaded. Setting lazy='dynamic' enables query-based loading.

4fill in blank

hard

Fill both blanks to define a back reference and enable cascade delete.

Flask

class Parent(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    children = db.relationship('Child', backref=[1], cascade=[2])

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

A'parent'

B'all, delete-orphan'

C'children'

D'save-update'

Attempts:

3 left

💡 Hint

Common Mistakes

Using plural or incorrect backref names.

Omitting quotes around string values.

The backref creates a reverse attribute named parent on the child. The cascade option 'all, delete-orphan' ensures children are deleted when the parent is deleted.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension mapping child names to their ages for children older than 5.

Flask

child_ages = {child.[1]: child.[2] for child in parent.children if child.[3] > 5}

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

Aname

Bage

Did

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong attribute names.

Mixing up keys and values in the dictionary.

This comprehension creates a dictionary where keys are child names and values are their ages, but only for children older than 5.