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?
- Defines how data is organized within a relational database.
- What is the purpose of identity Column in SQL database?
- A way to differentiate each column (unique to each)
- What is the purpose of a primary key in SQL database?
- To extract data from a table that is visited more than once during a process.
- What are the Data Types in SQL table? String, numeric (integer), post (where you could directly put in a python dictionary)
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?
- How you connecting to a database. Equivalent to a network connection to the database server
- Same for cursor object?
- A database object to retrieve data one row at a time.
- Look at conn object and cursor object in VSCode debugger. What attributes are in the object?
- Is "results" an object? How do you know? Yes, because it has data 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 favrecipes').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
- Compare create() in both SQL lessons. What is better or worse in the two implementations?
- 2b is shorter than 2a, more straightforward.
- Explain purpose of SQL INSERT.
- It is an SQL command that will insert the givene value into that table row+column
import sqlite3
def create():
recipelink = input("Enter your recipe link:")
recipename = input("Enter your recipe name:")
name = input("Enter your name:")
rating = input("Enter your rating:")
comments = input("Enter your comments:")
# 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 favrecipes (_recipelink, _recipename, _name, _rating, _comments) VALUES (?, ?, ?, ?, ?)", (recipelink, recipename, name, rating, comments))
# Commit the changes to the database
conn.commit()
print(f"A new user record {name} 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 tries to update their password to something smaller than 2 in length, then the pwd will instead be updated to be 'gothackednewpassword123'
- Explain try/except, when would except occur?
- The except error would occur when an sqlite3 error occured, opposed to an error regarding the uid not being found.
- What code seems to be repeated in each of these examples to point, why is it repeated?
- conn = sqlite3.connect(database)
- cursor = conn.cursor()
- To connect to the sqlite database file, and create a cursor object (so that SQL commands can be used), these lines must be repeated in every code cell
import sqlite3
def update():
uid = input("Enter recipe link")
password = input("Enter updated rec")
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 data is lost, and the action is often irreversible
- In the print statemements, what is the "f" and what does {uid} do?
- "f" is,
- {uid} will be replaced with the value for the variable, uid, the uid the user entered.
import sqlite3
def delete():
name = input("Enter user name 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 scores1 WHERE _name = ?", (name,))
if cursor.rowcount == 0:
# The uid was not found in the table
print(f"No name {name} was not found in the table")
else:
# The uid was found in the table and the row was deleted
print(f"The row with name {name} 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
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.
- Use Imperative or OOP style to Create a new Table or do something that applies to your CPT project.
Reference... sqlite documentation