exercise_15_2.py

# Exercise 15.2 Roster 

import json
import sqlite3

conn = sqlite3.connect('rosterdb.sqlite')
cur = conn.cursor()

# executescript() pasa varias instrucciones a la vez a la base de datos
cur.executescript('''
DROP TABLE IF EXISTS User;
DROP TABLE IF EXISTS Course;
DROP TABLE IF EXISTS Member;

CREATE TABLE User (
    id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT UNIQUE,
    name TEXT UNIQUE
);

CREATE TABLE Course (
    id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT UNIQUE,
    title TEXT UNIQUE
);

CREATE TABLE Member (
    user_id INTEGER,
    course_id INTEGER,
    role INTEGER,
    PRIMARY KEY (user_id, course_id)
);
''')

fname = input('Enter the file name: ')
if len(fname) < 1 : fname = 'roster_data_sample.json'

str_data = open(fname).read()
json_data = json.loads(str_data)

for entry in json_data :
    name = entry[0]
    title = entry[1]
    role = entry[2]

    cur.execute('INSERT OR IGNORE INTO User (name) VALUES (?)', (name,))
    cur.execute('SELECT id FROM User WHERE name = ?', (name,))
    user_id = cur.fetchone()[0]

    cur.execute('INSERT OR IGNORE INTO Course (title) VALUES (?)', (title,))
    cur.execute('SELECT id FROM Course WHERE title = ?', (title,))
    course_id = cur.fetchone()[0]

    cur.execute('INSERT OR REPLACE INTO Member (user_id, course_id, role) VALUES (?,?,?)', (user_id, course_id, role))

    conn.commit()