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Flask: Develop Web Applications in Python

The One-to-One Relationship

Understand how to establish a one-to-one relationship between Employee and Department models in Flask using SQLAlchemy. Learn to add ForeignKey columns, use relationship with backref, and set useList to False to ensure a single association.

We'll cover the following...

Introduction #

In the last lesson, we created a one-to-many relationship between the Employee and Department models. The code so far is given below:

Python 3.5
class Employee(db.Model):
    employee_id = db.Column(db.Integer, primary_key = True)
    first_name = db.Column(db.String(50), nullable = False)
    last_name = db.Column(db.String(50), nullable = False)
    department_name = db.Column(db.String, db.ForeignKey('department.name'), nullable = False)
        
class Department(db.Model):
    name = db.Column(db.String(50), primary_key = True, nullable = False)
    location = db.Column(db.String(120), nullable = False)
    employees = db.relationship('Employee', backref = 'department')
class Project(db.Model):
    project_id = db.Column(db.Integer, primary_key = True, nullable = False)
    name = db.Column(db.String(100), nullable = False)

Now, let’s learn how to add a one-to-one relationship between these models as well.

Representing a one-to-one relationship in models

In this example, a one-to-one relationship should exist between the Employee and Department. This relationship will indicate that an employee can be the head of a ...