Unit 2.4a Using Programs with Data, SQLAlchemy

• Database and SQLAlchemy
  • Imports and Flask Objects
  • Model Definition
  • Initial Data
  • Check for given Credentials in users table in sqlite.db
  • Create a new User in table in Sqlite.db
  • Reading users table in sqlite.db
• Hacks

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.
  1. Flask app object
     • the app takes the data and creats the db propterties
  2. SQLAlchemy db object
     • the db makes it so the app can be changed by SQLAlchemy

"""
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:///hw.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)

Model Definition

Define columns, initialization, and CRUD methods for users table in sqlite.db

• Comment on these items in the class, purpose and defintion.
  • class User
    • it is the template of the user
  • db.Model inheritance
    • inhetitance is when the model inherites different values/things from the db
  • init method
    • the consturctor of the object
  • @property, @<column>.setter
    • These attriubutes are what set, and get the value of whatever is asked, name, password etc
  • create, read, update, delete methods
    • CRUD is esstial to all db because you need to create, read, update, and delete constaly in your db

""" 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__ = 'homework'  # table teacher is plural, class teacher is singular

    # Define the User schema with "vars" from object
    id = db.Column(db.Integer, primary_key=True)
    _teacher = 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)
    _hw = db.Column(db.String(255), unique=False, nullable=False)

    # constructor of a User object, initializes the instance variables within object (self)
    def __init__(self, teacher, uid, hw, password="123qwerty"):
        self._teacher = teacher
        self._uid = uid
        self.hw = hw
        self.set_password(password)

    # a teacher getter method, extracts teacher from object
    @property
    def teacher(self):
        return self._teacher
    
    # a setter function, allows teacher to be updated after initial object creation
    @teacher.setter
    def teacher(self, teacher):
        self._teacher = teacher
    
    # 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 hw(self):
        return self._hw
    
    # a setter function, allows teacher to be updated after initial object creation
    @hw.setter
    def hw(self, hw):
        self._hw = hw
        
    @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
    
    
    # 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,
            "teacher": self.teacher,
            "uid": self.uid,
            "hw": self.hw,
        }

    # CRUD update: updates user teacher, password, phone
    # returns self
    def update(self, teacher="", uid="",  hw="", password=""):
        """only updates values with length"""
        if len(teacher) > 0:
            self.teacher = teacher
        if len(uid) > 0:
            self.uid = uid
        if len(hw) > 0:
            self.hw = hw
        if len(password) > 0:
            self.set_password(password)
        return self

    # CRUD delete: remove self
    # None
    def delete(self):
        db.session.delete(self)
        db.session.commit()
        return None

Initial Data

Uses SQLALchemy db.create_all() to initialize rows into sqlite.db

• Comment on how these work?
  1. Create All Tables from db Object
     • it takes all the data from the u's and for loops them, and trys to create them
  2. User Object Constructors
     • use the .create() or anything else to create stuff
  3. Try / Except
     • Try's to do something, expect if a certin value is reached

"""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(teacher='Mr. Mortensen', uid='bigmort123', hw='Hacks for 2.4a and b', password='123toby')
        u2 = User(teacher='Ms. Calicot', uid='ilovechem', hw='Compound Worksheet', password='123niko')
        u3 = User(teacher='Mr. Curry', uid='CurrysWorld', hw='Russia Worksheet', password='123lex')
        u4 = User(teacher='Ms. Boehm', uid='englishrocks', hw='Logical Fallicies Worksheet', password='123lex')
        u5 = User(teacher='Ms. Huang', uid='mathontop', hw='Problems 7-45 to 7-50', password='123lex')


        users = [u1, u2, u3, u4, u5]

        """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()

Created new uid bigmort123
Created new uid ilovechem
Created new uid CurrysWorld
Created new uid englishrocks
Created new uid mathontop

Check for given Credentials in users table in sqlite.db

Use of ORM Query object and custom methods to identify user to credentials uid and password

• Comment on purpose of following
  1. User.query.filter_by
     • The purpose of query.filter_by(_uid=uid) is to create a filter on the User table that matches the given _uid value.
  2. user.password
     • The purpose of user.password is to retrieve the hashed password stored in the User object.

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")

False

Create a new User in table in Sqlite.db

Uses SQLALchemy and custom user.create() method to add row.

• Comment on purpose of following
  1. user.find_by_uid() and try/except
     • It checks whether the user already exists
  2. user = User(...)
     • Assign data to the object
  3. user.dob and try/except
     • it tries to get the age from the dob, except if the dob is an error
  4. user.create() and try/except
     • try to create the user, without it present an error

def hw_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
    teacher = input("Enter your teaching name:")
    password = input("Enter your password")
    hw = input("Enter the homework that is due")
    
    
    # Initialize User object before date
    user = User(teacher=teacher, 
                uid=uid,
                hw=hw,
                password=password,
                )
    
    # 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}")
        
# hw_create()

Reading users table in sqlite.db

Uses SQLALchemy query.all method to read data

• Comment on purpose of following
  1. User.query.all
     • Takes all data from the table
  2. json_ready assignment, google List Comprehension
     • returns the user in json format

# SQLAlchemy extracts all users from database, turns each user into JSON
def hw_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

# hw_read()

def hw_delete():
    # Checking for user before delete
    teach = input("Input your uid: ")
    passs = input("Input your password: ")
    if check_credentials(teach, passs) == False:
        return
    else:
        pass
    
    with app.app_context():
        # find the user matching the input uid
        user = User.query.filter_by(_uid=teach).first()
        if user.hw == "No Homework":
            return "Homework is already none"
        else:
            user.hw = "No Homework"
            db.session.commit()
            return "Homework deleted, hopefully no more :)."

# hw_delete()

def hw_update():
    # Checking for user before delete
    teach = input("Input your uid: ")
    passs = input("Input your password: ")
    if check_credentials(teach, passs) == False:
        return
    else:
        pass
    newhw = input("What HW would you like to add")
    with app.app_context():
        # find the user matching the input uid
        user = User.query.filter_by(_uid=teach).first()
        user.hw = ""
        user.hw = newhw
        db.session.commit()
        return user.hw

# hw_update()

def hw_update():
    # Checking for user before delete
    teach = input("Input your uid: ")
    passs = input("Input your password: ")
    if check_credentials(teach, passs) == False:
        return
    else:
        pass
    newhw = input("What HW would you like to add")
    with app.app_context():
        # find the user matching the input uid
        user = User.query.filter_by(_uid=teach).first()
        user.hw = ""
        user.hw = newhw
        db.session.commit()
        return user.hw


# Delete method
def hw_delete():
    # Checking for user before delete
    teach = input("Input your uid: ")
    passs = input("Input your password: ")
    if check_credentials(teach, passs) == False:
        return
    else:
        pass
    
    with app.app_context():
        # find the user matching the input uid
        user = User.query.filter_by(_uid=teach).first()
        if user.hw == "No Homework":
            return "Homework is already none"
        else:
            user.hw = "No Homework"
            db.session.commit()
            return "Homework deleted, hopefully no more :)."


# SQLAlchemy extracts all users from database, turns each user into JSON
def hw_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

# Inputs, Try/Except, and SQLAlchemy work together to build a valid database object
def hw_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
    teacher = input("Enter your teaching name:")
    password = input("Enter your password")
    hw = input("Enter the homework that is due")
    
    
    # Initialize User object before date
    user = User(teacher=teacher, 
                uid=uid,
                hw=hw,
                password=password,
                )
    
    # 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}")

print("Select an option:")
print("1. Update homework")
print("2. Delete homework")
print("3. Read homework")
print("4. Create Account")
print("0. Exit")


def menu():
    choice = input("Enter your choice: ")
    
    if choice == "1":
        hw_update()
    elif choice == "2":
        hw_delete()
    elif choice == "3":
        print(hw_read())
    elif choice == "4":
        hw_create()
    elif choice == "0":
        return
    else:
        print("Invalid choice. Please try again.")
        
    menu()  # recursion to keep the menu going

# Start the menu
menu()

    

Select an option:
1. Update homework
2. Delete homework
3. Read homework
4. Create homework
0. Exit
[{'id': 1, 'teacher': 'Mr. Mortensen', 'uid': 'bigmort123', 'hw': 'Hacks for 2.4a and b'}, {'id': 2, 'teacher': 'Ms. Calicot', 'uid': 'ilovechem', 'hw': 'Compound Worksheet'}, {'id': 3, 'teacher': 'Mr. Curry', 'uid': 'CurrysWorld', 'hw': 'Russia Worksheet'}, {'id': 4, 'teacher': 'Ms. Boehm', 'uid': 'englishrocks', 'hw': 'Logical Fallicies Worksheet'}, {'id': 5, 'teacher': 'Ms. Huang', 'uid': 'mathontop', 'hw': 'Problems 7-45 to 7-50'}]
Invalid choice. Please try again.

Hacks

• Add this Blog to you own Blogging site. In the Blog add notes and observations on each code cell.
• Change blog to your own database.
• Add additional CRUD
  • Add Update functionality to this blog.
  • Add Delete functionality to this blog.