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
- Menu Interface to CRUD operations
- Hacks
- Imperative style of fetching all the user data
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?
- sort of like the category. Ex: table titles
- What is the purpose of identity Column in SQL database?
- if would make it easier to access data
- What is the purpose of a primary key in SQL database?
- it is a unique identifier
- What are the Data Types in SQL table?
- TEXT, INT, BOOL, FLOAT
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('forumPosts')").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?
- it is a connection to the database
- Same for cursor object?
- it is a cursor to the database
- Look at conn object and cursor object in VSCode debugger. What attributes are in the object?
- call, class, delattr, dir, eq, format
- Is "results" an object? How do you know?
- because it encompasses data used to create a user
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 forumPosts').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 think that OOP is better. It is easier to read and understand.
- Explain purpose of SQL INSERT. Is this the same as User init?
- it's the same because both initialize 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?
- if the user has a password input length of less than 2, then "hacked" is displayed.
- Explain try/except, when would except occur?
- the code runs the sql command and the conditional statements for the try. If the code encounters the specific error then the except is run.
- What code seems to be repeated in each of these examples to point, why is it repeated?
- the code is repeated because it is the same for each user. It is easier to read and understand.
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 it is capable of removing data from the database
- In the print statemements, what is the "f" and what does {uid} do?
- it is the python f string. It is a way to format strings. It 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?
- because the function menu() calls itself and will repeat until something is done to stop it.
- Could you refactor this menu? Make it work with a List?
- yes, you could make a list of the options and then use a for loop to print them out. You could also use a while loop to keep the menu running until the user chooses to exit.
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?
- kinda, because of the inputs. More clearly it would have a function with parameters.
-
In 2.4a or 2.4b lecture
-
Do you see data abstraction? Complement this with Debugging example.
- we can see data abstraction in the read() function. It is a function that is used to read data from the database.
Here, in the debug, we can see how the for loop fetches the array of data from the database and then prints it out. It is a function that is used to read data from the database.
-
Use Imperative or OOP style to Create a new Table or do something that applies to your CPT project.
-
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('forumPosts')").fetchall()
# Print the results
for row in results:
print(row)
# Close the database connection
conn.close()
schema()
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 forumPosts').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()