Unit 2.4a Using Programs with Data, SQLAlchemy
Using Programs with Data is focused on SQL and database actions. Part A focuses on SQLAlchemy and an OOP programming style,
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Database and SQLAlchemy
In this blog we will explore using programs with data, focused on Databases. We will use SQLite Database to learn more about using Programs with Data. Use Debugging through these examples to examine Objects created in Code.
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College Board talks about ideas like
- Program Usage. "iterative and interactive way when processing information"
- Managing Data. "classifying data are part of the process in using programs", "data files in a Table"
- Insight "insight and knowledge can be obtained from ... digitally represented information"
- Filter systems. 'tools for finding information and recognizing patterns"
- Application. "the preserve has two databases", "an employee wants to count the number of book"
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PBL, Databases, Iterative/OOP
- Iterative. Refers to a sequence of instructions or code being repeated until a specific end result is achieved
- OOP. A computer programming model that organizes software design around data, or objects, rather than functions and logic
- SQL. Structured Query Language, abbreviated as SQL, is a language used in programming, managing, and structuring data
"""
These imports define the key objects
"""
from flask import Flask
from flask_sqlalchemy import SQLAlchemy
"""
These object and definitions are used throughout the Jupyter Notebook.
"""
# Setup of key Flask object (app)
app = Flask(__name__)
# Setup SQLAlchemy object and properties for the database (db)
database = 'sqlite:///sqlite.db' # path and filename of database
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False
app.config['SQLALCHEMY_DATABASE_URI'] = database
app.config['SECRET_KEY'] = 'SECRET_KEY'
db = SQLAlchemy()
# This belongs in place where it runs once per project
db.init_app(app)
""" database dependencies to support sqlite examples """
import datetime
from datetime import datetime
import json
from sqlalchemy.exc import IntegrityError
from werkzeug.security import generate_password_hash, check_password_hash
''' Tutorial: https://www.sqlalchemy.org/library.html#tutorials, try to get into a Python shell and follow along '''
# Define the User class to manage actions in the 'users' table
# -- Object Relational Mapping (ORM) is the key concept of SQLAlchemy
# -- a.) db.Model is like an inner layer of the onion in ORM
# -- b.) User represents data we want to store, something that is built on db.Model
# -- c.) SQLAlchemy ORM is layer on top of SQLAlchemy Core, then SQLAlchemy engine, SQL
class User(db.Model):
__tablename__ = 'users' # table name is plural, class name is singular
# Define the User schema with "vars" from object
id = db.Column(db.Integer, primary_key=True)
_name = db.Column(db.String(255), unique=False, nullable=False)
_uid = db.Column(db.String(255), unique=True, nullable=False)
_password = db.Column(db.String(255), unique=False, nullable=False)
_dob = db.Column(db.Date)
# constructor of a User object, initializes the instance variables within object (self)
def __init__(self, name, uid, password="123qwerty", dob=datetime.today()):
self._name = name # variables with self prefix become part of the object,
self._uid = uid
self.set_password(password)
if isinstance(dob, str): # not a date type
dob = date=datetime.today()
self._dob = dob
# a name getter method, extracts name from object
@property
def name(self):
return self._name
# a setter function, allows name to be updated after initial object creation
@name.setter
def name(self, name):
self._name = name
# a getter method, extracts uid from object
@property
def uid(self):
return self._uid
# a setter function, allows uid to be updated after initial object creation
@uid.setter
def uid(self, uid):
self._uid = uid
# check if uid parameter matches user id in object, return boolean
def is_uid(self, uid):
return self._uid == uid
@property
def password(self):
return self._password[0:10] + "..." # because of security only show 1st characters
# update password, this is conventional method used for setter
def set_password(self, password):
"""Create a hashed password."""
self._password = generate_password_hash(password, method='sha256')
# check password parameter against stored/encrypted password
def is_password(self, password):
"""Check against hashed password."""
result = check_password_hash(self._password, password)
return result
# dob property is returned as string, a string represents date outside object
@property
def dob(self):
dob_string = self._dob.strftime('%m-%d-%Y')
return dob_string
# dob setter, verifies date type before it is set or default to today
@dob.setter
def dob(self, dob):
if isinstance(dob, str): # not a date type
dob = date=datetime.today()
self._dob = dob
# age is calculated field, age is returned according to date of birth
@property
def age(self):
today = datetime.today()
return today.year - self._dob.year - ((today.month, today.day) < (self._dob.month, self._dob.day))
# output content using str(object) is in human readable form
# output content using json dumps, this is ready for API response
def __str__(self):
return json.dumps(self.read())
# CRUD create/add a new record to the table
# returns self or None on error
def create(self):
try:
# creates a person object from User(db.Model) class, passes initializers
db.session.add(self) # add prepares to persist person object to Users table
db.session.commit() # SqlAlchemy "unit of work pattern" requires a manual commit
return self
except IntegrityError:
db.session.remove()
return None
# CRUD read converts self to dictionary
# returns dictionary
def read(self):
return {
"id": self.id,
"name": self.name,
"uid": self.uid,
"dob": self.dob,
"age": self.age,
}
# CRUD update: updates user name, password, phone
# returns self
def update(self, name="", uid="", password=""):
"""only updates values with length"""
if len(name) > 0:
self.name = name
if len(uid) > 0:
self.uid = uid
if len(password) > 0:
self.set_password(password)
db.session.commit()
return self
# CRUD delete: remove self
# None
def delete(self):
db.session.delete(self)
db.session.commit()
return None
"""Database Creation and Testing """
# Builds working data for testing
def initUsers():
with app.app_context():
"""Create database and tables"""
db.create_all()
"""Tester data for table"""
u1 = User(name='Thomas Edison', uid='toby', password='123toby', dob=datetime(1847, 2, 11))
u2 = User(name='Nikola Tesla', uid='niko', password='123niko')
u3 = User(name='Alexander Graham Bell', uid='lex', password='123lex')
u4 = User(name='Eli Whitney', uid='whit', password='123whit')
u5 = User(name='Indiana Jones', uid='indi', dob=datetime(1920, 10, 21))
u6 = User(name='Marion Ravenwood', uid='raven', dob=datetime(1921, 10, 21))
users = [u1, u2, u3, u4, u5, u6]
"""Builds sample user/note(s) data"""
for user in users:
try:
'''add user to table'''
object = user.create()
print(f"Created new uid {object.uid}")
except: # error raised if object nit created
'''fails with bad or duplicate data'''
print(f"Records exist uid {user.uid}, or error.")
initUsers()
def find_by_uid(uid):
with app.app_context():
user = User.query.filter_by(_uid=uid).first()
return user # returns user object
# Check credentials by finding user and verify password
def check_credentials(uid, password):
# query email and return user record
user = find_by_uid(uid)
if user == None:
return False
if (user.is_password(password)):
return True
return False
#check_credentials("indi", "123qwerty")
def create():
# optimize user time to see if uid exists
uid = input("Enter your user id:")
user = find_by_uid(uid)
try:
print("Found\n", user.read())
return
except:
pass # keep going
# request value that ensure creating valid object
name = input("Enter your name:")
password = input("Enter your password")
# Initialize User object before date
user = User(name=name,
uid=uid,
password=password
)
# create user.dob, fail with today as dob
dob = input("Enter your date of birth 'YYYY-MM-DD'")
try:
user.dob = datetime.strptime(dob, '%Y-%m-%d').date()
except ValueError:
user.dob = datetime.today()
print(f"Invalid date {dob} require YYYY-mm-dd, date defaulted to {user.dob}")
# write object to database
with app.app_context():
try:
object = user.create()
print("Created\n", object.read())
except: # error raised if object not created
print("Unknown error uid {uid}")
create()
# SQLAlchemy extracts all users from database, turns each user into JSON
def read():
with app.app_context():
table = User.query.all()
json_ready = [user.read() for user in table] # "List Comprehensions", for each user add user.read() to list
return json_ready
read()
"""
These imports define the key objects
"""
from flask import Flask
from flask_sqlalchemy import SQLAlchemy
"""
These object and definitions are used throughout the Jupyter Notebook.
"""
# Setup of key Flask object (app)
app = Flask(__name__)
# Setup SQLAlchemy object and properties for the database (db)
database = 'sqlite:///cars.db' # path and filename of database
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False
app.config['SQLALCHEMY_DATABASE_URI'] = database
app.config['SECRET_KEY'] = 'SECRET_KEY'
db = SQLAlchemy()
# This belongs in place where it runs once per project
db.init_app(app)
from sqlalchemy import Column, Integer, Text, String, Boolean
from sqlalchemy.exc import IntegrityError
class Car(db.Model):
__tablename__ = "cars"
__table_args__ = {'extend_existing': True}
id = db.Column(db.Integer, primary_key=True)
_make = db.Column(db.String(255), nullable=False, unique = False)
_model = db.Column(db.String(255), nullable=False, unique = False)
_price = db.Column(db.Integer, nullable=False, unique = False)
_year = db.Column(db.Integer, nullable=False, unique = False)
_desc = db.Column(db.String(255), nullable=False, unique = True)
_engine = db.Column(db.String(255), nullable=False, unique = False)
_body_style = db.Column(db.String(255), nullable=False, unique = False)
_owner = db.Column(db.String(255), nullable=False, unique = False)
def __init__(self, make, model, price, year, desc, body_style, engine, owner):
# Adding instance attributes
self._make = make
self._model = model
self._price = price
self._year = year
self._desc = desc
self._body_style = body_style
self._engine = engine
self._owner = owner
# Add getters and setters for make, model, price, year
@property
def make(self):
return self._make
@make.setter
def make(self, make):
self._make = make
@property
def model(self):
return self._model
@model.setter
def model(self, model):
self._model = model
@property
def price(self):
return self._price
@price.setter
def price(self, price):
self._price = price
@property
def year(self):
return self._year
@year.setter
def year(self, year):
self._year = year
@property
def desc(self):
return self._desc
@desc.setter
def desc(self, desc):
self._desc = desc
@property
def body_style(self):
return self._body_style
@body_style.setter
def body_style(self, body_style):
self._body_style = body_style
@property
def engine(self):
return self._engine
@engine.setter
def engine(self, engine):
self._engine = engine
@property
def owner(self):
return self._owner
@owner.setter
def owner(self, owner):
self._owner = owner
def dictionary(self):
dict = {
"make" : self.make,
"model" : self.model,
"price" : self.price,
"year" : self.year,
"desc" : self.desc,
"body_style" : self.body_style,
"engine" : self.engine,
"owner" : self.owner
}
return dict
def __str__(self):
return json.dumps(self.dictionary)
def create(self):
try:
# creates a Car object from Car(db.Model) class, passes initializers
db.session.add(self) # add prepares to persist person object to Users table
db.session.commit() # SqlAlchemy "unit of work pattern" requires a manual commit
return self
except IntegrityError:
db.session.remove()
return None
# CRUD read converts self to dictionary
# returns dictionary
def read(self):
return {
"id" : self.id,
"make" : self.make,
"model" : self.model,
"price" : self.price,
"year" : self.year,
"desc" : self.desc,
"body_style" : self.body_style,
"engine" : self.engine,
"owner" : self.owner
}
# CRUD update: updates attributes
# returns self
def update(self, make="", model="", price="", year="", desc="", body_style="", engine="", owner=""):
"""only updates values with length"""
if len(make) > 0:
self.make = make
if len(model) > 0:
self.model = model
if price > 0:
self.price(price)
if year > 0:
self.year(year)
if desc >= 0:
self.desc(desc)
if len(body_style) > 0:
self.body_style(body_style)
if len(engine) > 0:
self.engine(engine)
if len(owner) > 0:
self.owner(owner)
db.session.commit()
return self
# CRUD delete: remove self
# None
def delete(self):
db.session.delete(self)
db.session.commit()
return None
# Function to initialize the Cars
def initCars():
with app.app_context():
"""Create database and tables"""
# db.init_app(app)
db.create_all()
"""Data for table"""
car1 = Car(make="BMW", model="2 Series", price=34000, year=2021, desc="The BMW 2 series is a stylish sports coupe that drives just as well as it looks.", body_style="coupe", engine="2.0L four-cylinder", owner="John Doe")
cars = [car1]
"""Builds sample user/note(s) data"""
for car in cars:
try:
car.create()
except IntegrityError:
'''fails with bad or duplicate data'''
db.session.remove()
print(f"Records exist, duplicate car, or error: {car.id}")
initCars()
import sqlite3
database = 'instance/cars.db'
def create():
make = input("Enter the make of the car:")
model = input("Enter the model:")
price = input("Enter the price:")
year = input("Enter the year:")
desc = input("Enter a description of the car:")
body_style = input("Enter the body style of the car:")
engine = input("Enter the engine type:")
owner = input("Who's the owner of the car?")
# 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 cars (_make, _model, _price, _year, _desc, _body_style, _engine, _owner) VALUES (?, ?, ?, ?, ?, ?, ?, ?)", (make, model, price, year, desc, body_style, engine, owner))
# Commit the changes to the database
conn.commit()
print(f"A new car has been added")
except sqlite3.Error as error:
print("Error while executing the INSERT:", error)
# Close the cursor and connection objects
cursor.close()
conn.close()
create()
def read():
with app.app_context():
table = Car.query.all()
json_ready = [car.read() for car in table] # "List Comprehensions", for each user add user.read() to list
return json_ready
read()
import sqlite3
database = 'instance/cars.db'
# Take the inputs for each attribute
def update():
id = input("Enter the id of the car:")
make = input("Enter the make of the car:")
model = input("Enter the model:")
price = input("Enter the price:")
year = input("Enter the year:")
desc = input("Enter a description of the car:")
body_style = input("Enter the body style of the car:")
engine = input("Enter the engine type:")
owner = input("Who's the owner of the car?")
# 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
# Trying to add dob right now...
cursor.execute("UPDATE cars SET _make = ?, _model = ?, _price = ?, _year = ?, _desc = ?, _body_style = ?, _engine = ?, _owner = ? WHERE id = ?", (make, model, price, year, desc, body_style, engine, owner, id))
if cursor.rowcount == 0:
# Car ID not found
print(f"No id was found in the table")
# Commit new data
else:
print(f"Car with the id {id} has been updated")
conn.commit()
except sqlite3.Error as error:
print("Error while updating the record:", error)
# Close the cursor and connection objects
cursor.close()
conn.close()
update()
read()
import sqlite3
def delete():
id = input("Select the ID of the car you wish to remove: ")
# Connect to the database file
conn = sqlite3.connect(database)
# Create a cursor object to execute SQL commands
cursor = conn.cursor()
# Validate the input
try:
id = int(id)
except ValueError:
print("Invalid input: ID must be an integer.")
return
try:
# Use a parameterized query to prevent SQL injection
c = conn.cursor()
c.execute("DELETE FROM cars WHERE id = ?", (id,))
conn.commit()
print(f"Row with ID {id} has been deleted.")
except sqlite3.Error as e:
print(f"Error deleting row with ID {id}: {e}")
finally:
# Close the connection
cursor.close
conn.close()
delete()
read()