Use a database browser to browse the structure of your Django-polls database.

Preferred: use DBeaver GUI app to interact with almost any database, including Sqlite. Can draw ER diagrams. Home: https://dbeaver.io/

If you have a problem with DBeaver, other tools that work are:

• Sqlitebrowser free GUI app to browse SQLite database. https://sqlitebrowser.org/, but doesn’t draw ER diagram.
• sqlite3 - command line tool included with SQLite. Don’t need to install anything, but has only command line interface. You use SQL commands to view or modify the database.
  • See below for how to use sqlite3 to view a database.

The Django polls database file is db.sqlite3 in your django-polls directory.

Questions

1. The Django Polls database contains many tables. Which tables contain the data for your “polls” app?

2. What are the fields in the database table for “choice”?

3. Draw an ER or UML class diagram for how to relate a “choice” to a “question”.

4. In order to join a “question” to it’s “choices”, there must be a field in one of those tables that refers to the id field of the other table. This is called a Foreign Key. What field in what table is used to relate a question and its choices? (Write your answer as tablename.fieldname.)

5. Suppose we create a Django app named “store” and the “store” has model classes named Product and Sale. What would be the names of the tables in the database?

Part 2. Django Code

In the following questions use a query expression to retreive Model objects from the database. Use the Django shell to try your answers. See Making Queries for syntax of querying.

1. Write a Python function (as if part of the Django polls app) to count all the votes for poll for an id (id=1, 2, …).

   def vote_count(id):
       """Return total votes for a given poll. id is poll id"""
       # Hint: get the question from the database 
       #       Easiest is use Question.objects.get(...) 
       # question has a choice_set attribute that is a set of choices
       # for that question.
   
   

2. Write a method using Django query statements to find all polls where the question contains some specific text. Use Question.objects.filter(...) or similar query statement instead of fetching all objects.

   def find_polls_for_text(text):
       """Return list of Question objects for all polls containing some text"""
       # Hint: Question.objects.filter( expression )
       # and use the relations question_text__contains or __icontains 
   
   

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Using sqlite or sqlite3 Command Line Tool

sqlite or sqlite3 command line app is part of the SQLite package. You can use it to view or change a database, and issue SQL commands.

• Commands beginning with “.” are commands to sqlite, e.g. .help
• Other commands are SQL
• Examples:

  cmd> sqlite3  db.sqlite3
  sqlite> .help                         (show help message)
  sqlite> .tables                       (show tables)
  sqlite> .schema --indent polls_choice (show structure of a table)
  sqlite> .mode column                  (print query results in columns)
  sqlite> SELECT * FROM polls_choice;   (SQL query, must end in semi-colon)
  sqlite> .exit
  

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Reference

Making Queries in the Django documentation: https://docs.djangoproject.com/en/2.2/topics/db/queries/