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,
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.
-
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"
-
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
Imports and Flask Objects
Defines and key object creations
- Comment on where you have observed these working? Provide a defintion of purpose.
- Flask app object:The purpose includes implementing a WSGI application and acts as the central object. 2. SQLAlchemy db object: The purpose includes maintaining communication between Python programs and databases.
"""
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:///files/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 # tells us user wants to create
# -- 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): # how you set up sqlite table, this allows you to use these
__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()): # sets up data
self._name = name # variables with self prefix become part of the object,
self._uid = uid
self.set_password(password) # this finalizes the 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 # each attribute has a property, getter method
def name(self):
return self._name
# a setter function, allows name to be updated after initial object creation
@name.setter # updating, creating, changing, adding the value
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, #class users
"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) # performs update when id exists
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() # after you find it, check to see if it's there # checking the id with the query
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)): # if it returns because it found something, this is ran
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) # user types uid from the last cell to identify it in the data
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()
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()
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()