10. Foreign Key Constraint Setup

Setting up the Foreign Key Constraint

ND004 C01 L07 10 Setting Up The Foreign Key Constraint

Takeaways

  • db.relationship does not set up foreign key constraints for you. We need to add a column, some_parent_id , on the child model that has a foreign key constraint
  • Whereas we set db.relationship on the parent model, we set the foreign key constraint on the child model.
  • A foreign key constraint prefers referential integrity from one table to another, by ensuring that the foreign key column always maps a primary key in the foreign table.

db.ForeignKey question

ND004 C01 L07 10.1 Setting Up The Foreign Key Constraint

db.ForeignKey

  • Option in db.column to specify a foreign key constraint, referring to the primary key of the other table / model
  • Gets defined on the Child model

True/False: db.relationship sets up foreign keys

SOLUTION: False

Model Q

QUIZ QUESTION: :

On which model do we define each of the following?

ANSWER CHOICES:



SQLAlchemy concept

Model

Child Model

Parent Model

SOLUTION:

SQLAlchemy concept

Model

Child Model

Parent Model

db.ForeignKey

db.ForeignKey is passed into…

SOLUTION: `db.Column`

Choose the correct option to fill in the <BLANK> to set up the foreign key constraint between these two models: 

class School(db.Model):
  __tablename__ = 'schools'
  id = db.Column(db.Integer, primary_key=True)
  # ...

class Teacher(db.Model):
  __tablename__ = 'teachers'
  id = db.Column(db.Integer, primary_key=True)
  name = #...
  school_id = db.Column(db.Integer, <BLANK>)
SOLUTION: `db.ForeignKey('schools.id')`

Now let's apply what we learned to an example

ND004 C01 L07 10.2 Setting Up The Foreign Key Constraint

Write out the Driver and Vehicle models

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Did you get it right?

Watch the next video to find out!

ND004 C01 L07 10.3 Setting Up The Foreign Key Constraint

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