Unit 2.4b Using Programs with Data, SQL
Using Programs with Data is focused on SQL and database actions. Part B focuses on learning SQL commands, connections, and curses using an Imperative programming style,
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
- Explore SQLite Connect object to establish database connection- Explore SQLite Cursor Object to fetch data from a table within a database
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?
- indexing
- What are the Data Types in SQL table?
- variables, strings, integers
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?
- A database that you connect to.
- Same for cursor object?
- Look at conn object and cursor object in VSCode debugger. What attributes are in the object?
- Is "results" an object? How do you know?
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()
Create a new User in table in Sqlite.db
Uses SQL INSERT to add row
- Compore create() in both SQL lessons. What is better or worse in the two implementations?
- The imperative style is much more readable but the OOP style is more concise.
- Explain purpose of SQL INSERT. Is this the same as User init?
- Adds data to the table, user init creates the object
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()
Updating a User in table in Sqlite.db
Uses SQL UPDATE to modify password
- What does the hacked part do?
- changes the password to a preset if the password is too short, because it would be easy to guess/hack
- Explain try/except, when would except occur?
- Try tests a block of code and if it fails, it runs except instead
- What code seems to be repeated in each of these examples to point, why is it repeated?
- cursor and conn keep getting redefined to make sure that it is up to date with the sqlite.db file
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()
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 you might accidentally permanently delete data with no way of getting it bac
- In the print statemements, what is the "f" and what does {uid} do?
- It's a simpler way of combining strings and variables
- {uid} just writes out the value of the uid variable
- instead of
print("cool string " + var)you can doprint(f"cool string {var}")
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()
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
# rewritten with lists
operations = {"c":create(), "r":read(), "u":update(), "d":delete()}
unused = []
for method in operations:
if operation == method:
operations[method]
else:
unused.append(method)
if len(unused) == 4:
print("Please enter c, r, u, or d")
menu() # recursion, repeat menu
# Repeats running menu because of recursive loop (calls itself within)
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.
- 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.
- Yea, data from database is being represented through read operations
- Use Imperative or OOP style to Create a new Table or do something that applies to your CPT project.
- Do you see data abstraction? Complement this with Debugging example.
Reference... sqlite documentation