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
The Tri 2 Final Project is 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? The categories of the table, or the column names
- What is the purpose of identity Column in SQL database? Id column makes the information or data to be much easier to access
- What is the purpose of a primary key in SQL database? Purpose of a primary key is to be unique to each row
- What are the Data Types in SQL table? You can find integers, strings, booleans, floats, lists, dictionaries
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? Connection objects allows for connection to sqlite database
- Same for cursor object? Cursor allows you to execute methods in the sqlite database
- Look at conn object and cursor object in VSCode debugger. What attributes are in the object?
- Is "results" an object? How do you know? Results is an object because it contains data. Object can also have methods.
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
- Compare create() in both SQL lessons. What is better or worse in the two implementations? create() in the first lesson utilizes object oriented programming while the second one takes a more imperitave approach, based on individual functions. In OOP , large databases stay organized while in Imperitave may become diffucult to navigate and add to after a certain amount of data. However, imperitave is easier to understand and can therefore be easier to work with at times.
- Explain purpose of SQL INSERT. Is this the same as User init? SQL INSERT inserts data into a specified schema of the table. User init initiallizes the dataset. They are not the same thing.
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 ensures that the length of the password is greater than 2. If it is not, the message is updated to hacked.
-
Explain try/except, when would except occur? Except would occur when there was a problem connecting to the sqlite database or performing a function on the database
-
What code seems to be repeated in each of these examples to point, why is it repeated? Defining conn and cursor is repeated in all of these exmaples, because otherwise a connection to the swlite database can not be formed.
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()
read()
update()
read()
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 can be a dangerous operation when the database is public because of the fact that people may attempt to wipe the entire database.
- What is the "f" and {uid} do? f is a replacement for .format, and allows any variables in the string to automatically be converted into string format. This is called an f-string. {uid} allows the program to access data based on the userinput of uid.
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()
read()
delete()
read()
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? menu() repeats because menu() is a recurssive function, meaning it calls menu() within itself.
- Could you refactor this menu? Make it work with a List? If this means make the input a list or c, r, u, d that the program should run then yes this could be done. The program could split the user input into each of the methods that must be run and continue accordingly.
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.
- Create a new Table or do something new, sqlite documentation
- In implementation in previous bullet, do you see procedural abstraction?