Question

6.23 LAB: Python insert/update sqlite3 datafiles

Given is a Python program that connects to a sqlite database and has one table called writers with two columnns:

• name - the name of a writer
• num - the number of works the writer has written

The writers table originally has the following data:

name, num
Jane Austen,6
Charles Dickens,20
Ernest Hemingway,9
Jack Kerouac,22
F. Scott Fitzgerald,8
Mary Shelley,7
Charlotte Bronte,5
Mark Twain,11
Agatha Christie,73
Ian Flemming,14
J.K. Rowling,14
Stephen King,54
Oscar Wilde,1

Update the Python program to ask the user if they want to update entries or add new entries. If the name entered already exists in the writers table then the database record is updated, overwriting the original contents. If the name does not exist in the writers table, then add a new record with the writer's name and number of works. The following TODO sections must be completed.

• Check if a writer exists in the writers table
• If the writer exists in the table, locate an entry to be updated by writer's name and update the writer's value for num
• If the writer does not exist in the table, add a new entry in the writers table and provide the value for name and num

Ex: If the input is:

y
J.K. Rowling
30
y
Elton John
y
62
n

The output is:

(ID, Name, Num)
(1, 'Jane Austen', 6)
(2, 'Charles Dickens', 20)
(3, 'Ernest Hemingway', 9)
(4, 'Jack Kerouac', 22)
(5, 'F. Scott Fitzgerald', 8)
(6, 'Mary Shelley', 7)
(7, 'Charlotte Bronte', 5)
(8, 'Mark Twain', 11)
(9, 'Agatha Christie', 73)
(10, 'Ian Flemming', 14)
(11, 'J.K. Rowling', 30)
(12, 'Stephen King', 54)
(13, 'Oscar Wilde', 1)
(14, 'Elton John', 62)

Answer 1

The following function does the above required tasks. The code is throroughly commented to explain the steps.

import sqlite3

#This function will do the required tasks upon being called
def process_database():
    # Assuming the database file with given data is also named 'writers.db', otherwise change name below
    # Connect to database named "writers.db"
    connection = sqlite3.connect("writers.db")

    # Create cursor to navigate
    cursor = connection.cursor()

    while True:
        # Ask input from user
        command = input("Do you want to update entries or add new entries? (Enter y or n)")
        if command == 'n':
            break
        elif command == 'y':
            name = input() # Get 'name' input
            num = input() # Get 'num' input
            exists = False # variable to store if inputted name already exists in database

            # SELECT ALL ROWS FROM EXISTING DATABASE, and check to see if the input 'name' already exists
            rows = cursor.execute("SELECT name, num from writers").fetchall()
            for row in rows:
                # if name exists, set var 'exists' to True
                if row[0] == name:
                    exists = True
                    break

            # Update record if it already exists
            if exists:
                cursor.execute("UPDATE writers set num=? where name=?", (num, name))
            # Insert record if it doesn't already exist in the database
            else:
                insert_statement = "INSERT INTO writers VALUES (?, ?);"
                cursor.execute(insert_statement, (name, num))

            # Commit changes to database
            connection.commit()

    # Close db connection
    connection.close()

Hope that helps!