In this assignment you will temporarily step away from building the applications and develop a data model from a file of un-normalized data and then build a script to load data in to that model. It is quite common to build a web site and then need to pre-load it with data from a file or API.
The data is a simplified extraction of the UNESCO World Heritage Sites registry. The un-normalized data is provided as both a spreadsheet and a CSV file:
The columns in the data are as follows:
You have to have the CSV data available to run the batch script. If you are using PythonAnywhere
to do your homework, you can use the
wget command to pull in the data (see below).
We will do this assignment in a new Django project called
batch so as not to disturb your other work.
cd ~/django_projects django-admin startproject batch
Make new application under your
cd ~/django_projects/batch python manage.py startapp unesco
You need to copy the CSV file into the
unesco folder. If the
wget command is available
you can use it to download the file:
cd unesco wget https://www.dj4e.com/assn/dj4e_load/whc-sites-2018-clean.csv
Also make a folder called
scripts and add an
__init__.py file to it. The
is needed in order to store Python objects in the
cd ~/django_projects/batch mkdir scripts touch scripts/__init__.py
Make a copy of the
many_load.py from this folder into your
Then in install
django extensions if you have not already done so:
workon django4 # or django3 (if needed) pip install django_extensions
Add the following line to your
INSTALLED_APPS = [ 'django.contrib.admin', 'django.contrib.auth', 'django.contrib.contenttypes', ... 'django_extensions', # Add 'unesco.apps.UnescoConfig', # Add ]
At this point you should run:
python manage.py check
And make sure that your basic Django environment is configured properly.
We need to design a database model that represents this flat data across multiple tables using "third-normal form" - which basically means that columns that have vertical duplication, such as region:
category state region iso Cultural Afghanistan Asia and the Pacific af Cultural Afghanistan Asia and the Pacific af Cultural Albania Europe and North America al Cultural Albania Europe and North America al Cultural Algeria Arab States dz Mixed Algeria Arab States dz Cultural Algeria Arab States dz Cultural Algeria Arab States dz
In order to simplify the assignment, we have done the model design for you and spread the data across five tables linked together with one-to-many relationships.
The result of the database design exercise is the following
models.py file. It
uses foreign keys to link the tables together. You can add this
from django.db import models class Category(models.Model): name = models.CharField(max_length=128, default="") def __str__(self) : return self.name class State(models.Model): name = models.CharField(max_length=128, default="") def __str__(self) : return self.name class Iso(models.Model): name = models.CharField(max_length=128, default="") def __str__(self) : return self.name class Region(models.Model): name = models.CharField(max_length=128, default="") def __str__(self) : return self.name class Site(models.Model): name = models.CharField(max_length=300) year = models.IntegerField(null=True) latitude = models.FloatField(null=True) longitude = models.FloatField(null=True) description = models.TextField(null=True) justification = models.TextField(null=True) area_hectares = models.FloatField(null=True) category = models.ForeignKey("Category", on_delete=models.CASCADE, null=True) region = models.ForeignKey("Region", on_delete=models.CASCADE, null=True) iso = models.ForeignKey("Iso", on_delete=models.CASCADE, null=True) state = models.ForeignKey("State", on_delete=models.CASCADE, null=True) def __str__(self) : return self.name
Since we have given you the data model, in order to better understand the data model, as an exercise, please draw the model using Crow's-Foot Notation. You can use paper, or a layout tool - one way or another your diagram should have five boxes and four lines - and the each of lines should be properly labelled as a "many" or a "one" end.
Once you have put the file in
unesco/models.py built, run
migrate to create
cd ~/django_projects/batch python manage.py makemigrations python manage.py migrate
Django has a special
runscript capability that allows you to write a Python program
to read and write the database using your Django models.
There is a simple example of how to write such a script in the
You will need to copy the
unesco/scripts/many_load.py and then make changes
to adapt it from the Membership model/data to the Site model/data. The
many_load.py file is
the sample code from the lecture on this topic - it needs a quite a few of changes to
make it work with your
Site data model. We outline the kinds of changes that are needed
(1) You need to change the name of the file that the sample script opens and reads to the file that you downloaded and installed.
(2) In the example code, before the loop to read the data is executed, we empty out the database using statements like:
For your code you will want to empty out all the models / tables with statements like:
(3) In order to create the entries in each of the lookup tables so you can point to them
using foreign keys, the sample
many_load.py code uses statements like the following:
p, created = Person.objects.get_or_create(email=row)
This code insures that there is a row in the Person table for the email address
that was just read
row. The email address may or may not already be in the table
from a previous line in the file. One way or another, by the end of this line
p contains a reference to a Person stored in the database that can be
used to fullfill a foreign key refernence later in the code.
Note that the "p, created" is an example of Python function returning two values using a tuple.
For your program you will create the "lookup" entries in each table (Category, Iso, State, and Region) using four statements like:
cat, created = Category.objects.get_or_create(name=row)
(4) In the sample code, once all the lookup objects are created, the sample code creates the Membership entry using the following code.
m = Membership(role=r,person=p, course=c) m.save()
The line to create and save the
Membership row is the last thing that is done so all the
foreign key connections can be made because the Person, Course, and Role entries
exist and are in the variables p, c, and r respectively.
(5) Your data will be more complex than the sample, You will need to deal with situations
where an integer column like the
year will be empty. The solution is to
year to see if it is a valid integer and if it is
not a valid integer set it to
None which will become
NULL (or empty) in the
data base when inserted.
cat, created = Category.objects.get_or_create(name=row) ... try: y = int(row) except: y = None ... try: lat = float(row) except: lat = None ... site = Site(name=row, description=row, year=y, ... latitude = lat, ... category=cat ...) site.save()
You will need to do a try / except for each of the numeric fields that might be missing or have invalid data.
At the end you will create the Site object from the lookup objects, cleaned up column data and the string data
that goes into the
Place the CSV file in the
unesco folder and then run the script from the project folder (i.e.
manage.py file resides):
cd ~/django_projects/batch workon django4 # Or django3 (if necessary) python manage.py runscript many_load
It needs to be run this way so that lines like:
from unesco.models import Site, Iso, ....
You can also hand-check your data by running a few queries on your data before turning it in to make sure the data makes it into the right tables:
$ sqlite3 db.sqlite3 SQLite version 3.24.0 2018-06-04 14:10:15 Enter ".help" for usage hints. sqlite> SELECT count(id) FROM unesco_state; 163 sqlite> SELECT count(id) FROM unesco_site; 1044 sqlite> SELECT count(id) FROM unesco_state where name="India"; 1 sqlite> SELECT count(id) FROM unesco_site WHERE name="Hawaii Volcanoes National Park" AND year=1987 AND area_hectares = 87940.0; 1 sqlite> SELECT COUNT(*) FROM unesco_site JOIN unesco_iso ON iso_id=unesco_iso.id WHERE unesco_site.name="Maritime Greenwich" AND unesco_iso.name = "gb"; 1 sqlite> .quit $
When the data passes your manual tests, you can download
db.sqlite3 from PythonAnywhere
and then upload it to the autograder.
If the autograder complains that your file is somehow too big,
or you have been changing your
models.py and your
is asking you how to convert existing columns,
or you just
want to start with a fresh database, you can run the following commands.
$ cd ~/django_projects/batch $ rm db.sqlite3 $ rm */migrations/0* $ python manage.py makemigrations $ python manage.py migrate $ python manage.py runscript many_load
Make sure you run these commands in the correct folder
~/django_projects/batch). You can run this process in any Django
project but your database is completely reset (i.e. admin and login accounts
are deleted as well). This also completely rebuilds your migrations
from your latest