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
  • Updating users table in sqlite.db
  • Deleting 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
  2. SQLAlchemy db object

"""
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)

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
    • The class that manages the actions in the 'users' table
  • db.Model inheritance
    • It is a parameter of class User
    • Object oriented programming
  • init method
    • Is the constructor for the class User
    • Initializes the instance variables within object
  • @property, @<column>.setter
    • @property is a getter method that extracts from the object
    • @<column>.setter allows the variable that was created to be updated
  • create, read, update, delete methods
    • Allows the database and specific data inside to be created, read, updated, and deleted

""" database dependencies to support sqlite examples """
import datetime
from datetime import datetime
import json

from sqlalchemy.exc import IntegrityError

''' 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 Car(db.Model):
    __tablename__ = 'cars'  # 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)
    _mascot = db.Column(db.String(255), unique=False, nullable=False)
    _car = db.Column(db.String(255), unique=False, nullable=False)
    _mile = db.Column(db.Integer, primary_key=False)

    # constructor of a User object, initializes the instance variables within object (self)
    def __init__(self, name, uid, mascot, car, mile):
        self._name = name    # variables with self prefix become part of the object, 
        self._uid = uid
        self._mascot = mascot
        self._car = car
        self._mile = mile

    # 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
    
    # a getter method, extracts mascot from object
    @property
    def mascot(self):
        return self._mascot
    
    # a setter function, allows mascot to be updated after initial object creation
    @mascot.setter
    def mascot(self, mascot):
        self._mascot = mascot

    # a getter method, extracts car from object
    @property
    def car(self):
        return self._car

    # a setter function, allows car to be updated after initial object creation
    @car.setter
    def car(self, car):
        self._car = car
    
    # a getter method, extracts mile from object
    @property
    def mile(self):
        return self._mile
    
    # a setter function, allows car to be updated after initial object creation
    @mile.setter
    def mile(self, mile):
        self._mile = mile
    
    # 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,
            "mascot": self.mascot,
            "mile": self.mile,
            "car": self.car,
        }

    # CRUD update: updates user name, car, phone
    # returns self
    def update(self, name="", uid="", mascot="", car=""):
        """only updates values with length"""
        if len(name) > 0:
            self.name = name
        if len(uid) > 0:
            self.uid = uid
        if len(mascot) > 0:
            self.mascot = mascot
        if len(car) > 0:
            self._car = car
        db.session.commit()
        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
  2. User Object Constructors
  3. Try / Except

"""Database Creation and Testing """


# Builds working data for testing
def initCars():
    with app.app_context():
        """Create database and tables"""
        db.create_all()
        """Tester data for table"""
        u1 = Car(name='Cameron Yarbough', uid="cam", mascot='nighthawks', mile=4.21, car='Tesla Model Y')
        u2 = Car(name='Luke Jin', uid="luke", mascot='nighthawks', mile=4.39, car='Lamborghini')
        u3 = Car(name='Adrian Welton', uid="adrian", mascot='wolverines', mile=4.33, car='Ferrari')
        u4 = Car(name='Tom Bell', uid="tommy", mascot='sundevils', mile=4.19, car='NIO ec6')
        u5 = Car(name='Stanley Yan', uid="stanley", mascot='nighthawks', mile=4.38, car='Mercedes Benz')
        u6 = Car(name='Nathan Cristmore', uid="nathan", mascot='falcons', mile=4.22, car='Aston Martin')


        cars = [u1, u2, u3, u4, u5, u6]

        """Builds sample Track/note(s) data"""
        for car in cars:
            try:
                '''add Track to table'''
                object = car.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 {car.uid}, or error.")
                
initCars()

Created new uid cam
Created new uid luke
Created new uid adrian
Created new uid tommy
Created new uid stanley
Created new uid nathan

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
     • This receives a uid and looks to see if that uid exists in the database.
  2. user.password
     • If the uid is found, the passwords are checks and verified to make sure the password exists and is correct.

def find_by_uid(uid):
    with app.app_context():
        user = Car.query.filter_by(_uid=uid).first()
    return user # returns user object

# Check credentials by finding user and verify password
def check_credentials(uid):
    # query email and return user record
    user = find_by_uid(uid)
    if user == None:
        return False
    return True
        
check_credentials("cam")

True

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
     • A uid is inputted and it is checked whether the uid exists or not
     • If the user is found, then nothing is created
     • If there is no user with that uid, a new user is created
  2. user = User(...)
     • This only runs if the user is not found
     • A new user is created using the class User with a name, uid, and password
  3. user.dob and try/except
     • This only runs if the user is not found
     • If the dob that is inputted is the same as the date today, then an error appears
  4. user.create() and try/except
     • This only runs if the user is not found
     • If the object is not created, an error is raised; otherwise, the user is created

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:")
    mascot = input("Enter your school mascot:")
    car = input("Enter your car:")
    mile = input("Enter your mile time:")
    
    # Initialize User object before date
    user = Car(name=name, 
                uid=uid, 
                mascot=mascot,
                car=car,
                mile=mile
                )
    
    # create user.dob, fail with today as 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()

Found
 {'id': 4, 'name': 'Tom Bell', 'uid': 'tommy', 'mascot': 'sundevils', 'mile': 4.19, 'car': 'NIO ec6'}

Reading users table in sqlite.db

Uses SQLALchemy query.all method to read data

• Comment on purpose of following
  1. User.query.all
     • This gets all the users from the database
  2. json_ready assignment, google List Comprehension
     • This reads all the users from the table and places them in a list using list comprehension
     • Each are turned into JSON data

# SQLAlchemy extracts all users from database, turns each user into JSON
def read():
    with app.app_context():
        table = Car.query.all()
    json_ready = [user.read() for user in table] # "List Comprehensions", for each user add user.read() to list
    return json_ready

read()

[{'id': 1,
  'name': 'Cameron Yarbough',
  'uid': 'cam',
  'mascot': 'nighthawks',
  'mile': 4.21,
  'car': 'Tesla Model Y'},
 {'id': 2,
  'name': 'Luke Jin',
  'uid': 'luke',
  'mascot': 'nighthawks',
  'mile': 4.39,
  'car': 'Lamborghini'},
 {'id': 3,
  'name': 'Adrian Welton',
  'uid': 'adrian',
  'mascot': 'wolverines',
  'mile': 4.33,
  'car': 'Ferrari'},
 {'id': 4,
  'name': 'Tom Bell',
  'uid': 'tommy',
  'mascot': 'sundevils',
  'mile': 4.19,
  'car': 'NIO ec6'},
 {'id': 5,
  'name': 'Stanley Yan',
  'uid': 'stanley',
  'mascot': 'nighthawks',
  'mile': 4.38,
  'car': 'Mercedes Benz'},
 {'id': 6,
  'name': 'Nathan Cristmore',
  'uid': 'nathan',
  'mascot': 'falcons',
  'mile': 4.22,
  'car': 'Aston Martin'},
 {'id': 7,
  'name': 'Micah Senn',
  'uid': 'micah',
  'mascot': 'cougars',
  'mile': 4.38,
  'car': 'Bugatti'}]

Updating users table in sqlite.db

def update():
    # optimize user time to see if uid exists
    uid = input("Enter your user id:")
    user = find_by_uid(uid)
    if user != None:
        pass
    else:
        print(f"No user id {uid} found")
        return
    name = input("Enter your name:")
    mascot = input("Enter your school mascot:")
    car = input("Enter your car:")
    
    # Initialize User object before date
    user = Car(name=name, 
                uid=uid, 
                mascot=mascot,
                car=car,
                )
    # write object to database
    with app.app_context():
        try:
            object = user.update()
            print("Updated\n", object.read())
        except:  # error raised if object not created
            print("Unknown error uid {uid}")
        
update()

Updated
 {'id': None, 'name': 'Tom Bell', 'uid': 'tommy', 'mascot': 'sundevils', 'mile': '4.19', 'car': 'Hyundai Palisade'}

Deleting users table in sqlite.db

import sqlite3

database = 'instance/sqlite.db' # this is location of database

def delete():
    id = input("Enter 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 cars WHERE id = ?", (id))
        if cursor.rowcount == 0:
            # The id was not found in the table
            print(f"No id {id} was not found in the table")
        else:
            # The id was found in the table and the row was deleted
            print(f"The row with id {id} was successfully deleted")
        conn.commit()
    except sqlite3.Error as error:
        print("Error while executing the DELETE:", error)
    finally:
        conn.commit()
        conn.close()
        
delete()

The row with id 7 was successfully deleted

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.