Flask: Develop Web Applications in Python/

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The One-to-Many Relationship

The One-to-Many Relationship

In this lesson, we will get to know how to add a one-to-many relationship between models.

We'll cover the following...

Introduction #

While working with databases, one of the key concepts is the relationship between tables. The types of relationships that exist are:

  • One-to-many
  • One-to-one
  • Many-to-many

In the next few lessons, we will cover how to represent and create these relationships between the models using SQLAlchemy.

Consider the Human Resource Management System(HRMS) of a company. The application would contain the following models.

  • Employee
  • Department
  • Project

A simple implementation of these models is given below.

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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)
    
class Department(db.Model):
    name = db.Column(db.String(50), nullable = False)
    location = db.Column(db.String(120), nullable = False)
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 relationships between these models.

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