Database Programming is Program with Data

The Tri 2 Final Project is 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?

  • What is the purpose of identity Column in SQL database?
  • What is the purpose of a primary key in SQL database? It is easy to access, that is what a primary key is. Primary keys should also be uniqe (bames would not work)
  • What are the Data Types in SQL table? Integer, String, Boolean, Images, any structures can work. Lists can also work.
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()

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? The user doesn't actually access this but uses it?
  • Same for cursor object? Same for the cursor object as for the connection
  • Look at conn object and cursor object in VSCode debugger. What attributes are in the object? Conn, cursor, results.
  • Is "results" an object? How do you know? results has data in it so that could make it an object. It has attributes as well (methods) so that is what makes it an object.
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$d6tlB2EPrWI6hPsU$ecba09619ff1b02d04c7255968148dd3ab3339a6a2507c875e267bae59f1bf7a', '1847-02-11')
(2, 'Nikola Tesla', 'niko', 'sha256$Cbcn1BgG9XCkwONR$09bf9ade66a3f9cec03fb687713123b28fcd30c5978c4c0371590d3f98edbfee', '2023-03-19')
(3, 'Alexander Graham Bell', 'lex', 'sha256$HnfGlyo2rja79BoE$d87d9af976644d85ecd2a493816531013112b58d8170de7ccd29cf55cac3675c', '2023-03-19')
(4, 'Eli Whitney', 'whit', 'sha256$l7n4jNlWrD5yaaiG$77986ff81499eb7d2c8a9204ffc0e08601ea84c05a3279833abe7ed2af4b1a0b', '2023-03-19')
(5, 'Indiana Jones', 'indi', 'sha256$rmyppBD8vlJFvNLz$24540fb5d14a53af0ecdaa41e4f86e797b54d9a70d3fab6468e8411f379e260c', '1920-10-21')
(6, 'Marion Ravenwood', 'raven', 'sha256$4Fbjzr6FQsrjftO4$b406cc72d3e9a70c1bb97864e6f30848980631f15f0c793007c77d94fda23b3b', '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? This code seems less repetative than the previous one and still works the same way as the last one. This code seems to be more efficient because it uses a list with only one try and expcept code for all the variables as opposed to the last code had multiple try and except functions because one was used for each variable.
  • Explain purpose of SQL INSERT. Is this the same as User init?
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()
Error while executing the INSERT: UNIQUE constraint failed: users._uid

Updating a User in table in Sqlite.db

Uses SQL UPDATE to modify password

  • What does the hacked part do? it updates the user ID.
  • Explain try/except, when would except occur? except works when try does not work.
  • What code seems to be repeated in each of these examples to point, why is it repeated?
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 123srik 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 because there is no safety mechanism or warning to stop someone from deleting something. So someone ccan delete all the information in the database and that would be bad.
  • What is the "f" and {uid} do? so that the program knows that it is the uid that is being deleted and not a name or a password. Or maybe the uid is the first in that row, so deleting that will delete the entire row whereas deleting the other parts would not have done that.
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 123srik 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?
  • Could you refactor this menu? Make it work with a List?
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")

Hacks

  • Add this Blog to you own Blogging site. In the Blog add notes and observations on each code cell.
  • Create a new Table or do something new, sqlite documentation
  • In implementation in previous bullet, do you see procedural abstraction?