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database: json format and sqlite - izan - Dec-28-2021

Hi!
I have to do the following task:
The application will read roster data in JSON format, parse the file, and then produce an SQLite database that contains a User, Course, and Member table and populate the tables from the data file.

You can base your solution on this code: http://www.py4e.com/code3/roster/roster.py - this code is incomplete as you need to modify the program to store the role column in the Member table to complete the assignment.

My programme:
import json
import sqlite3

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

# Do some setup
cur.executescript('''
DROP TABLE IF EXISTS User;
DROP TABLE IF EXISTS Member;
DROP TABLE IF EXISTS Course;


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 file name: ')
if len(fname) < 1:
    fname = 'roster_data.json'

# [
#   [ "Charley", "si110", 1 ],
#   [ "Mea", "si110", 0 ],

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]

    print((name, title, role))

    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 IGNORE INTO Member (role)
        VALUES ( ? )''', ( role, ) )
    
    

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

    conn.commit()
The the task says:
Once you have made the necessary changes to the program and it has been run successfully reading the above JSON data, run the following SQL command:

Output:
SELECT User.name,Course.title, Member.role FROM 
    User JOIN Member JOIN Course 
    ON User.id = Member.user_id AND Member.course_id = Course.id
    ORDER BY User.name DESC, Course.title DESC, Member.role DESC LIMIT 2;
The output should look as follows:
Output:
Zuriel|si430|0
Zofia|si363|0
With my programme I get the following (I suppose it is what I have to obtain):
Output:
('Mehraz', 'si310', 0)
('Tobie', 'si310', 0)
('Naila', 'si310', 0)
('Asif', 'si310', 0)
('Derren', 'si310', 0)
('Abdulkadir', 'si310', 0)
The problem comes here:
Then the task says: Once that query gives the correct data, run this query:
Output:
SELECT 'XYZZY' || hex(User.name || Course.title || Member.role ) AS X FROM 
    User JOIN Member JOIN Course 
    ON User.id = Member.user_id AND Member.course_id = Course.id
    ORDER BY X LIMIT 1;
You should get one row with a string that looks like XYZZY53656C696E613333.

I think there is something wrong with this query because it does not work. Any ideas? Thank you in advance

RE: database: json format and sqlite - ibreeden - Dec-28-2021

(Dec-28-2021, 01:25 PM)izan Wrote: With my programme I get the following (I suppose it is what I have to obtain):
Output:
('Mehraz', 'si310', 0)('Tobie', 'si310', 0)
('Naila', 'si310', 0)
('Asif', 'si310', 0)
('Derren', 'si310', 0)
('Abdulkadir', 'si310', 0)

I can't believe you get this result by executing:
Output:
SELECT User.name,Course.title, Member.role FROM 
    User JOIN Member JOIN Course 
    ON User.id = Member.user_id AND Member.course_id = Course.id
    ORDER BY User.name DESC, Course.title DESC, Member.role DESC LIMIT 2;
It says: "LIMIT 2" but you get 6 records. It also says "ORDER BY User.name DESC" but your names appear in random order.
Please have a sharp look at how you execute this query.