Relational database

A lot of data can be stored in tabels

Table Human

ID	Name	Age
1	Anton	34
2	Morten	37

Table Course

ID	Subject	Hours
1	Python	30
2	Matlab	0

Table Teacher (wrong)

ID	HumanName	HumanAge	CourseSubject	CourseHours
1	Anton	34	Python	30
2	Morten	37	Python	30

Table Teacher (correct)

ID	HumanID	CourseID
1	1	1
2	2	1

How to present structure of tables

Table Human

Field	Type
ID	Integer
Name	String
Age	Integer

Table Course

Field	Type
ID	Integer
Subject	String
Hours	Integer

Table Teacher

Field	Type
ID	Integer
human	Integer
course	Integer

How to define structure of tables in Python? Django Models!



In [ ]:

    
# models.py
from django.db import models

class Human(models.Model):
    ''' Description of any Human'''
    name = models.CharField(max_length=200)
    age  = models.IntegerField()

    objects = models.Manager()

    def __str__(self):
        ''' Nicely print Human object '''
        return u"I'm %s, %d years old" % (self.name, self.age)


class Course(models.Model):
    ''' Description of teaching course'''
    subject = models.CharField(max_length=200)
    hours = models.IntegerField()

    objects = models.Manager()

    def __str__(self):
        ''' Nicely print Course object '''
        return 'Course in %s, %d hrs long' % (self.subject, self.hours)


class Teacher(models.Model):
    ''' Description of Teacher '''
    human = models.ForeignKey(Human)
    course = models.ForeignKey(Course)

    objects = models.Manager()

    def __str__(self):
        ''' Nicely print Teacher object '''
        return '%s teaching %s' % (self.human.name, self.course.subject)

How to use the Django Models?

1. Let's add data to database



In [ ]:

    
from our_project.models import Human

# create a Human and add data
h = Human()
h.name = 'Anton'
h.age = 34

# save data to database
h.save()

2. Now we can quit python and enter again



In [ ]:

    
from our_project.models import Human

# fetch all Humans from the database
humans = Human.objects.all()

# get the first one (the only one so far)
h0 = humans[0]

3. Let's add more data and make a relation



In [ ]:

    
from our_project.models import Course, Teacher



In [ ]:

    
# we create and save a course
c = Course()
c.subject = 'Python'
c.hours = 30
c.save()

# we create a teacher
t = Teacher()

# we create relations
t.human = h0
t.course = c
t.save()

Now the database contains

three tables: Human, Course and Teacher
two relations: Teacher --> Human and Teacher --> Course

Let's fetch the data from the database.



In [ ]:

    
teachers = Teacher.objects.all()
t0 = teachers[0]
print t0.human.name
print t0.human.age
print t0.course.subject
print t0.course.hours

We can also search the database using a siple syntax



In [ ]:

    
theTeacher = Teacher.objects.find(human__name__contains='An')
theTeacher[0]