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?
- how a database is structured
- What is the purpose of identity Column in SQL database?
- assign a value to each row for parsing
- What is the purpose of a primary key in SQL database?
- extract data that is visited more than once in a code base
- What are the Data Types in SQL table?
- floats, integers, strings, booleans, etc.
import sqlite3
database = 'files/users.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 connection to a data source like an sql database
- Same for cursor object?
- allows you to do things in an sql database
- Look at conn object and cursor object in VSCode debugger. What attributes are in the object?
- conn is connection object, and cursor is cursor object
- Is "results" an object? How do you know?
- "results" calls a function pertaining to an object creating data that makes "results" an object, because results returns all data in the data base in the form of dictionaries nested inside an array
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)
print(results)
# 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
- Compare create() in both SQL lessons. What is better or worse in the two implementations?
- in the object oriented implementation, variables are already defined before the 'create()' function is made. In this lesson everything must be defined in the function
- Explain purpose of SQL INSERT. Is this the same as User init?
- SQL INSERT adds a row to a data table, User init initializes the User class
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?
- it shows up if your password is too short
- Explain try/except, when would except occur?
- if the password entered is invalid
- What code seems to be repeated in each of these examples to point, why is it repeated?
- connecting to database and creating cursor object, these need to be called and closed each time to ensure the database is updated
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?
- not unless you make dumb decisions with it, or if your data is lossy
- In the print statements, what is the "f" and what does {uid} do?
- 'f' means 'format', and allows you to insert variables into a string.
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()
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?
- to read which command has been entered and to respond accordingly
- Could you refactor this menu? Make it work with a List?
- yes, I would make each command a dictionary nested in a list, this way you enter in the command as a key, and get the result as a value
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.
- In this implementation, do you see procedural abstraction?
- Yes, each function is an example of procedural abstraction. You can call these functions later in the program to execute a segment of code. One example is the "create" function, when called, this function passes in data for a new row in the data table and uses sqlite to add the data to the users table.
- In 2.4a or 2.4b lecture
- Do you see data abstraction? Complement this with Debugging example.
- Data abstraction is all over this program, each function of CRUD interacts with data, one example is the "create" function. This example shows me debugging the create function, I have a breakpoint right where the function adds the data I just inputted to the data table.
- 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
from IPython.display import Image
Image(filename='images/debug example.png')
