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?
- Database schema is the structure and how the data is organized and defined.
- What is the purpose of identity Column in SQL database?
- An identity column in SQL database makes it so it can easily identify objects, as well as keep track of them, edit, and delete them. This way, the database is more organized.
- What is the purpose of a primary key in SQL database?
- The primary key in an SQL database is to uniquely label/identify rows in the table
- What are the Data Types in SQL table?
- string, numeric, date/time
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 connection object is a unique session with a data source. I think this means that every time SQl connects, it has data specific to the database. This is what creates a conn that connects to the database.
- Same for cursor object?
- A cursor object is "a mechanism that enables traversal over the records in a database". I think these objects allow for the database to take inputs from the user.
- Look at conn object and cursor object in VSCode debugger. What attributes are in the object?
- The database schema are the attricutes in the object (ex:id, name, uid, passowrd, dob)- Is "results" an object? How do you know?
- Yes, results is an object. I know this since it has variables and functions.
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?
- I like the OOP programming create() funciton better. It is more efficient and is in fewer lines. However, it does require that you defined all your setters and getters previously.
- Explain purpose of SQL INSERT. Is this the same as User init?
- SQL INSERT is a command that will add the data into the database table. It is "activated" seperately, versus the init in the OOP model runs all the functions under 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()
Updating a User in table in Sqlite.db
Uses SQL UPDATE to modify password
- What does the hacked part do?
- The hacked part makes it so if a user types in a paswword that is less then 2 characters, they will get a message that says the have been hacked and will set their password to "gothackednewpassword123".
- Explain try/except, when would except occur?
- The try/except act as conditionals where they will attempt to pursue code, and then if those conditions aren't met/fail, it will run the except code.
- What code seems to be repeated in each of these examples to point, why is it repeated?
- It seems that defining conn and cursor before the try and except is repeated everytime. Also, the cursor.clos() and the conn.close. I think this may be becuase the connection object, and how the connection is unique everytime.
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, DELETE is a dangerous opertation since it cannot be reversed. The record is gone forever.
- In the print statemements, what is the "f" and what does {uid} do?
- the "f" and {} form formatted string literals. They allow the uid to be replaced with specific data to the situation.
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?
- The menu repeats so it can perform multiple CRUD operations.
- Could you refactor this menu? Make it work with a List?
- I'm not exactly sure how I could refactor this menu. Maybe I could put all the CRUD operation functions into a list, and then iterate through the list to call the functions. I could name it CRUD = ['create()', 'read()', 'update()', 'delete()', 'schema()']. This would make the code more 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")
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. <-recursion
- Use Imperative or OOP style to Create a new Table or do something that applies to your CPT project.
Reference... sqlite documentation