Unit 2.4B
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?
- **A database schema is how data is organized within a relational database**
- What is the purpose of identity Column in SQL database?
- It should be unique because it will be the identifiable aspect, such as the id of a user.
- What is the purpose of a primary key in SQL database?
- The purpose of a primary key is to be able to correctly identify a row or thing
- What are the Data Types in SQL table?
- Boolean, float, integer, string, list, dictionary, pretty much any data type
Notes on code below:
- schema is the function name
- 255 is the maximum length
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
# The PRAGMA table_info command prints out the stuff
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 represents a unique session with a data source. I think it establishes a session with a database/table
- Same for cursor object?
- A cursor object is an object that is used to make the connection for executing SQL queries. I think they are used to process individual rows returned by database queries.
- Look at conn object and cursor object in VSCode debugger. What attributes are in the object?
- In the conn object, there are no attributes, but in the cursor object there is the "conn" label.
- Is "results" an object? How do you know?
- Results is an object because it has data and attributes. It has the data/results of the users. An object can also have functions, like create, read, update, and delete.
- Abstraction is simplifying something
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?
- This one is better because it is a cleaner implementation with less confusions and less code. However, this implementation doesn't censor your password. OOP is easier for bigger programs.
- Explain purpose of SQL INSERT. Is this the same as User init?
- SQL INSERT adds a new row, so it is different from User init because that is the initial starting, whereas insert is after it has already started and you are adding a new row
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 checks if the length of the password is less than 2, if so then the password is changed.
- Explain try/except, when would except occur?
- If the uid was not found, then it will print out an error message, if there wasn an error then it would print out "error while executing the update"
- What code seems to be repeated in each of these examples to point, why is it repeated?
- The connection to the database is repeated because it is necessary to establish a connection to edit/view the database. It repeats because it's recursive.
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 irreversible
- In the print statemements, what is the "f" and what does {uid} do?
- the f formats the string, uid tells the program to insert the uid there
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()
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?
- Procedural abstraction is like having the same operations being performed in different places in a program. There is procedural abstraction in this implementation because the CRUD functions are being used in multiple places.
- In 2.4a or 2.4b lecture
- Do you see data abstraction? Complement this with Debugging example.
- Data abstraction is the reduction of a particular body of data to a simplified representation of the whole. This is seen when you read the data from the database and then print it out to be a representation of the whoel
- 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