Accelerating Information Technology Innovation

Transcription

1 Accelerating Information Technology Innovation Rwanda Summer 2011 Django 01: Models

2 Models Suppose we want to create a web application to manage data about thousands of movies What information would we want to store? Title Rating (scale from 1 to 5) Genre Lead Actor Supporting Actors 2

3 Models How would we think about storing this data? Lecture 4: Dictionaries and lists are used to store data in Python Web applications use databases Lots of options varying syntax Each table represents a different model Each column is a different attribute Django: Common interface to almost all database solutions (NoSQL and SQL) 3

4 Models Django s database interface works with any object of type django.db.models.model To create your own Model, use inheritance! from django.db import models class Movie(models.Model): # attributes go here Inherits from models.model 4

5 Models Models have attributes: Fields We create instances of Model objects in a different way (no init function necessary) from django.db import models class Movie(models.Model): # attributes go here self.title = models.charfield(max_length=100) self.rating = models.integerfield() Field to store text (strings and unicode objects) Field to store the rating the movie received 5

6 Models Some attributes indicate special relationships to other Model objects ForeignKey: OneToMany ManyToManyField: Well, it s a many-to-many field from django.db import models One movie can have many supporting actors; one supporting actor can be in many movies class Movie(models.Model): rating = models.integerfield() title = models.charfield(max_length=100) genre = models.charfield() lead_actor = models.foreignkey(actor,related_name= lead actor ) support_actors = models.manytomanyfield(actor,related_name= support ) One lead actor who could be the lead actor in other movies 6

7 Checkpoint: Models Build a django Model class for Actor What does the class inherit from? What attributes should the class have? Build a django Model class for Award What does the class inherit from? What attributes should the class have? 7

8 Checkpoint: Models Actor Model class: class Actor(models.Model): name = models.charfield(max_length=100) birth_date = models.datefield() Attributes name: a string- use a CharField birth_date: a datetime.date- use a DateField 8

9 Checkpoint: Models What type of field should we use for the title of the Award? CharField What type of field should we use to denote the winning actor? ForeignKey (one actor, many awards) What type of field should we use for the nominees (each nominee is a Movie)? ManyToManyField (each movie can be nominated for many awards, each award has many nominees) 9

10 Checkpoint: Models Award Model class: What type of field should we use for the title of the Award? What type of field should we use to denote the winning actor? What type of field should we use for the nominees (each nominee is a Movie)? class Award(models.Model): title = models.charfield(max_length=100) sponsor = models.charfield(max_length=100) year = models.datefield() winning_actor = models.foreignkey(actor) winning_movie = models.foreignkey(movie,related_name= winning movie ) nominees = models.manytomanyfield(movie,related_name= nominees ) 10

11 Checkpoint: Models Wait! How does Actor relate to the Movie class that we just wrote? We only need to specify the relation in one of the models Later: We can go backwards and get all Movie objects with the same lead actor or supporting actors class Actor(models.Model): name = models.charfield(max_length=100) birth_date = models.datefield() 11

12 Models Inserting information into the database Now: command line (manual) Later: admin (Django GUI Interface) Monday: forms (user-initiated) But we need to actually create our database first 12

13 Models: Add the application with the relevant models to the list of INSTALLED_APPS Specify the path to your new database Validate your Model classes django-admin.py validate Create or update the models in our project python manage.py syncdb Later: reset the database (clear all information) python manage.py reset app_name We ll see the utility of this later on 13

14 Models: Python Shell Use the Python shell to add information to the database python manage.py shell gives us a Djangoready Python shell Let s put information about Akeelah and the Bee in our database Movie: Akeelah and the Bee Actor: Keke Palmer Award: Outstanding Actress (won by Keke) 14

15 Models: Python Shell from movie_app.models import Actor,Award,Movie import datetime Import the model classes we made keke = Actor(name= Keke Palmer,birth_date=datetime.date(1993,8,26)) Looks like our usual initialization but a little different keke.save() Saves a new entry in the Actor table of the database How could we create a new entry for the movie Akeelah and the Bee 15

16 Models: Python Shell akeelah_bee = Movie(title= Akeelah and the Bee,lead_actor=keke, genre= Drama,rating=4) How do we store akeelah_award into our database? akeelah_bee.save() Create the award akeelah_bee We need to stop and save akeelah_bee before setting our supporting actor attributes ManyToManyField: convenient, useful, and a little weird 16

17 Models: Field Values We know how to add entries into the database with different attribute values How do we restrict attribute values? Set of choices Validate using our own rules (consider the max_length=100 rule that we have set on some of the CharField objects) 17

18 Models: Field Values Suppose we wanted to add a gender attribute to the Actor class gender should be a character, either M for Male or F for Female The set of choices is a tuple of individual choices Each choice is its own tuple GENDER_CHOICES = ( ( M, Male ),( F, Female )) M and F are the allowed field values Male and Female are the human-readable choices (what you will see in the admin dropdown menu see the next lecture) 18

19 Models: Field Values Restrict the movie rating to a number between 1 and 5 Use an adjective to describe the quality of the movie RATING_CHOICES = ((1,'Terrible'),(2,'Bearable'),(3,'Okay'), (4,'Good'),(5,'Fantastic')) class Movie(models.Model): title = models.charfield(max_length=100) # some attributes here rating = models.integerfield(choices=rating_choices) Set the choices option to the RATING_CHOICES tuple 19

20 Models: Access Suppose our database has information on three movies: Dreamgirls Akeelah and the Bee Something New All of these movies featured 2007 Best Actress nominees (won by Keke Palmer from Akeelah and the Bee ) 20

21 Models: Access How do we access different subsets of these movies? QuerySet: iterable structure with zero, one, or more table entries (model instances) >>> Movie.objects.all() [<Movie: Akeelah and the Bee>, <Movie: Dreamgirls>, <Movie: Something New>] Returns a QuerySet with all model instances >>> Movie.objects.filter(title="Dreamgirls") [<Movie: Dreamgirls>] Returns a QuerySet with model instances that have title Dreamgirls 21

22 Models: Access How do we access different subsets of these movies? QuerySet: iterable structure with zero, one, or more table entries (model instances) >>> Movie.objects.filter(rating lt=5) [<Movie: Akeelah and the Bee>, <Movie: Something New>] Returns a QuerySet with model instances that have rating less than 5 >>> Movie.objects.filter(rating=5) [<Movie: Dreamgirls>] Returns a QuerySet with model instances that have rating equal to 5 22

23 Models: Access Access a particular Model instance: Use the get command Access to Model attributes: Use the same.attribute syntax as in Python classes >>> dreamgirls = Movie.objects.get(title="Dreamgirls") >>> print dreamgirls.lead_actor Beyonce Knowles 23

24 Backup Slides References: IMDB.com 24

25 Models: Using the Admin admin is a builtin Django module Simple GUI to create and modify the entries in your database models.py class Actor(models.Model): # some code class Award(models.Model): # some code class Movie(models.Model): # some code admin.site.register(actor) admin.site.register(award) admin.site.register(movie) 25