Database Programming is Program with Data

Each Tri 2 Final Project should be an example of a Program with Data.

Prepare to use SQLite in common Imperative Technique

Schema of Users table in Sqlite.db

Uses PRAGMA statement to read schema.

Describe Schema, here is resource Resource- What is a database schema? - the categories of a table

  • What is the purpose of identity Column in SQL database? - makes it easier to search through and access the data
  • What is the purpose of a primary key in SQL database? - to be unique to each row
  • What are the Data Types in SQL table? - strings, floats, booleans, integers, dictionaries, lists
import sqlite3

database = 'instance/sqlite.db' # this is location of database

def schema():
    
    # Connect to the database file
    conn = sqlite3.connect(database)

    # Create a cursor object to execute SQL queries
    cursor = conn.cursor()
    
    # Fetch results of Schema
    results = cursor.execute("PRAGMA table_info('users')").fetchall()

    # Print the results
    for row in results:
        print(row)

    # Close the database connection
    conn.close()
    
schema()
(0, 'id', 'INTEGER', 1, None, 1)
(1, '_name', 'VARCHAR(255)', 1, None, 0)
(2, '_uid', 'VARCHAR(255)', 1, None, 0)
(3, '_password', 'VARCHAR(255)', 1, None, 0)
(4, '_dob', 'DATE', 0, None, 0)

Reading Users table in Sqlite.db

Uses SQL SELECT statement to read data

  • What is a connection object? After you google it, what do you think it does? - It helps people store their personal data in a sqlite table
  • Same for cursor object? - lets you have sqlite methods
  • Is "results" an object? How do you know? - Yes it is, because it stores data
import sqlite3

def read():
    # Connect to the database file
    conn = sqlite3.connect(database)

    # Create a cursor object to execute SQL queries
    cursor = conn.cursor()
    
    # Execute a SELECT statement to retrieve data from a table
    results = cursor.execute('SELECT * FROM users').fetchall()

    # Print the results
    if len(results) == 0:
        print("Table is empty")
    else:
        for row in results:
            print(row)

    # Close the cursor and connection objects
    cursor.close()
    conn.close()
    
read()
(1, 'Thomas Edison', 'toby', 'sha256$L6tYfrAjpL1uD2wQ$e48d68ff90a4f0a2effd5f86abed797a5b247e9d8ede2ab9513df2b8971d04c1', '1847-02-11')
(2, 'Nikola Tesla', 'niko', 'sha256$VF1JW3qTSJ6qKkMS$29785ff67e44702b45a53c2e5c66540becb548773d496200414d14548b0acf84', '2023-03-15')
(3, 'Alexander Graham Bell', 'lex', 'sha256$AZos0zfj8JemZrI3$9939047fa78118513908835d3244e2959b212342bc5cb35d72b8a6e88bb0ff39', '2023-03-15')
(4, 'Eli Whitney', 'whit', 'sha256$8qJZA6c04HDvA0aT$b607ac3dd2fe69899d241865a350807a420cfe58349f0b4784b6f0b2357afbb4', '2023-03-15')
(5, 'Indiana Jones', 'indi', 'sha256$v245JOHOEPhJlMdY$d361af2ae59902dd6fd778928287a5db6e67d2c328830c559e776c9d3c762dbc', '1920-10-21')
(6, 'Marion Ravenwood', 'raven', 'sha256$5VtGze1xqQJzsXk5$9bea1b4b207b7c5aeae98920e334ca402dcdfd4a6af8b46ec0165c7e819acc9d', '1921-10-21')

Create a new User in table in Sqlite.db

Uses SQL INSERT to add row

  • Compare create() in both SQL lessons. What is better or worse in the two implementations? In the first lesson the create function uses object oriented programming while the second one takes a more imperative approach, In OOP , large databases stay organized while in Imperative may become difficult to navigate and add to after a certain amount of data. However, imperative is easier to understand and can therefore be easier to work with at times.
  • Explain purpose of SQL INSERT. Is this the same as User init? SQL INSERT inserts data into a specified schema of the table. User init initiallizes the dataset. They are not the same thing.
import sqlite3

def create():
    name = input("Enter your name:")
    uid = input("Enter your user id:")
    password = input("Enter your password")
    dob = input("Enter your date of birth 'YYYY-MM-DD'")
    
    # Connect to the database file
    conn = sqlite3.connect(database)

    # Create a cursor object to execute SQL commands
    cursor = conn.cursor()

    try:
        # Execute an SQL command to insert data into a table
        cursor.execute("INSERT INTO users (_name, _uid, _password, _dob) VALUES (?, ?, ?, ?)", (name, uid, password, dob))
        
        # Commit the changes to the database
        conn.commit()
        print(f"A new user record {uid} has been created")
                
    except sqlite3.Error as error:
        print("Error while executing the INSERT:", error)


    # Close the cursor and connection objects
    cursor.close()
    conn.close()
    
create()
A new user record nick has been created

Updating a User in table in Sqlite.db

Uses SQL UPDATE to modify password

  • What does the hacked part do? Makes sure the length of the password is more than 2 characters
  • Explain try/except, when would except occur? When the function doesn't work properly, or in this case the updated password doesn't fit the requirements.
  • What code seems to be repeated in each of these examples to point, why is it repeated? The conn and cursor being connected to the sqlite database are defined in each file. This is because without this the database won't exist.
import sqlite3

def update():
    uid = input("Enter user id to update")
    password = input("Enter updated password")
    if len(password) < 2:
        message = "hacked"
        password = 'gothackednewpassword123'
    else:
        message = "successfully updated"

    # Connect to the database file
    conn = sqlite3.connect(database)

    # Create a cursor object to execute SQL commands
    cursor = conn.cursor()

    try:
        # Execute an SQL command to update data in a table
        cursor.execute("UPDATE users SET _password = ? WHERE _uid = ?", (password, uid))
        if cursor.rowcount == 0:
            # The uid was not found in the table
            print(f"No uid {uid} was not found in the table")
        else:
            print(f"The row with user id {uid} the password has been {message}")
            conn.commit()
    except sqlite3.Error as error:
        print("Error while executing the UPDATE:", error)
        
    
    # Close the cursor and connection objects
    cursor.close()
    conn.close()
    
update()
The row with user id toby the password has been successfully updated

Delete a User in table in Sqlite.db

Uses a delete function to remove a user based on a user input of the id.

  • Is DELETE a dangerous operation? Why? Yes, it is dangerous because it doesn't ask for any user validation and deletes the user without asking for confirmation.
  • In the print statemements, what is the "f" and what does {uid} do? the f in print statements automatically converts the variables to strings.
import sqlite3

def delete():
    uid = input("Enter user id to delete")

    # Connect to the database file
    conn = sqlite3.connect(database)

    # Create a cursor object to execute SQL commands
    cursor = conn.cursor()
    
    try:
        cursor.execute("DELETE FROM users WHERE _uid = ?", (uid,))
        if cursor.rowcount == 0:
            # The uid was not found in the table
            print(f"No uid {uid} was not found in the table")
        else:
            # The uid was found in the table and the row was deleted
            print(f"The row with uid {uid} was successfully deleted")
        conn.commit()
    except sqlite3.Error as error:
        print("Error while executing the DELETE:", error)
        
    # Close the cursor and connection objects
    cursor.close()
    conn.close()
    
delete()
The row with uid lex was successfully deleted

Menu Interface to CRUD operations

CRUD and Schema interactions from one location by running menu. Observe input at the top of VSCode, observe output underneath code cell.

  • Why does the menu repeat? Menu repeats because it's getting called several times.
  • Could you refactor this menu? Make it work with a List? Yes, you could but would be less efficient.
def menu():
    operation = input("Enter: (C)reate (R)ead (U)pdate or (D)elete or (S)chema")
    if operation.lower() == 'c':
        create()
    elif operation.lower() == 'r':
        read()
    elif operation.lower() == 'u':
        update()
    elif operation.lower() == 'd':
        delete()
    elif operation.lower() == 's':
        schema()
    elif len(operation)==0: # Escape Key
        return
    else:
        print("Please enter c, r, u, or d") 
    menu() # recursion, repeat menu
        
try:
    menu() # start menu
except:
    print("Perform Jupyter 'Run All' prior to starting menu")
A new user record lancesson has been created

Hacks

  • Add this Blog to you own Blogging site. In the Blog add notes and observations on each code cell.
  • In this implementation, do you see procedural abstraction?
  • In 2.4a or 2.4b lecture
    • Do you see data abstraction? Complement this with Debugging example.
    • Use Imperative or OOP style to Create a new Table or do something that applies to your CPT project.

Reference... sqlite documentation