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.

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?

Flask app object:Our Flask servers that we created our databases on obviously used Flask previously. It often ends up in conjunction with...
SQLAlchemy object: This is always associated with our recent database creations. It is used both to work with others' data and create our own.

"""
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
class User purpose:Abstracts a user into a specific, named object and creates variables for each of its attributes and traits.
db.Model inheritance: Takes attributes and aspects of db.Model when creating the Users class.
__init__ method: Acts as the constructor for the class, which defines each of the object's attributes.
@property (getter), @[column].setter (setter): Getter and setter functions, allows for reading an attribute respectively.
Additional methods: delete and update functions that I use later.

""" 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 email from object
    @property
    def uid(self):
        return self._uid
    
    # a setter function, allows name 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 setter
    def set_password(self, password):
        """Create a hashed password."""
        self._password = generate_password_hash(password, method='sha256')

    # check password parameter versus 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, to avoid unfriendly outcomes
    @property
    def dob(self):
        dob_string = self._dob.strftime('%m-%d-%Y')
        return dob_string
    
    # dob should be have verification for type date
    @dob.setter
    def dob(self, dob):
        if isinstance(dob, str):  # not a date type     
            dob = date=datetime.today()
        self._dob = dob
    
    @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) in human readable form, uses getter
    # 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="", dob=""):
        """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)
        if isinstance(dob, str):  # not a date type     
            dob = date=datetime.today()
        else:
            self.dob = dob
        db.session.add(self)
        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.

Create All Tables from db Object:The create_all() function creates the SQLite table, allowing for the user objects to be added into it.
User Object Constructors: The user object is created differently for each user variable below. The constructors create a user object with the attributes defined by the arguments provided to the User class.
Try / Except: Using the try condition means that, if the user creation fails, there is a failsafe to the error in the except case that doesn't completely destroy the process. It also acts as a validation process.

"""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()

Created new uid toby
Created new uid niko
Created new uid lex
Created new uid whit
Created new uid indi
Created new uid raven

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

User.query.filter_by:Finds a specific user and its data based on the given UID, which will then have its password used as a checker.
user.password: Used to varify the password input after getting the UID in question.

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")

Create a new User in table in Sqlite.db

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

Comment on purpose of following

user.find_by_uid() and try/except:The find_by_uid function is used to define the user function as the user with the given uid variable. However, the find_by_uid process will fail if a user with the inputted uid doesn't exist. As a result, the print function under the try condition will have an error when trying to read the user variable if it was never defined, and the except condition will occur, using pass to transition in to the user creation process.
user = User(...): The user variable is defined as a User object with the name, user ID and password inputted above. The placement of this definition/initialization process is important because of the user.dob definition (described below).
user.dob and try/except: After defining user as the User object, the program attempts to create the user's date of birth based on the inputted year, month and day by directly adding the attribute using user.dob. If the date of birth was inputted incorrectly, the .strptime function will fail and the except condition will be triggered, setting a default user date of birth as the current date.
user.create() and try/except: The user.create() function adds the user object to the database. This is put within a try condition because, if for some reason this fails, the except function will be used to cancel the process and state that an unknown error occurred.

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()

Created
 {'id': 7, 'name': 'AJ Ruiz', 'uid': 'ajbal', 'dob': '04-16-2006', 'age': 16}

Reading users table in sqlite.db

Uses SQLALchemy query.all method to read data

Comment on purpose of following

User.query.all:This represents the full table of User data, which is then defined as the local table variable which is iterated through to create the JSON.
json_ready assignment: The json_ready variable represents the correctly-formatted JSON data formed by the procedure beside it. It is then returned with the function.

# 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] # each user adds user.read() to list
    return json_ready

read()

[{'id': 1,
  'name': 'Thomas Edison',
  'uid': 'toby',
  'dob': '02-11-1847',
  'age': 176},
 {'id': 2,
  'name': 'Nikola Tesla',
  'uid': 'niko',
  'dob': '03-15-2023',
  'age': 0},
 {'id': 3,
  'name': 'Alexander Graham Bell',
  'uid': 'lex',
  'dob': '03-15-2023',
  'age': 0},
 {'id': 4,
  'name': 'Eli Whitney',
  'uid': 'whit',
  'dob': '03-15-2023',
  'age': 0},
 {'id': 5,
  'name': 'Indiana Jones',
  'uid': 'indi',
  'dob': '10-21-1920',
  'age': 102},
 {'id': 6,
  'name': 'Marion Ravenwood',
  'uid': 'raven',
  'dob': '10-21-1921',
  'age': 101},
 {'id': 7, 'name': 'AJ Ruiz', 'uid': 'ajbal', 'dob': '04-16-2006', 'age': 16}]

Hacks

Below is evidence of my completion of each of the hacks.

2.4 College Board Quiz Questions

Here are my results on the 2.4 College Board quiz.

The questions were all fairly self-explanatory. However, in many cases, it required reading through the problem very thoroughly.

The main reason a lot of the questions weren't challenging was that certain aspects of the problem were clearly irrelevant to the prompt given, so if I saw an answer providing the use of that aspect in some way, chances were that it was incorrect. Question 3 had most of the "contents" column as completely useless information, and Question 4 had the "Sort by Subject" procedure that was clearly irrelevant to the given prompt.

The only question I had to take some time to think about was question 2, because each of the responses were so detailed and specific to the information provided that I had to focus pretty hard on each of them.

Update Function

In the code cell below, I created a function to update user data in the database.

def update():
    # first require uid input
    uid = input("Enter your user id:")
    user = find_by_uid(uid)
    if user != None:
        print('Found user with user ID "' + uid + '".')
        pass
    else:
        print("User not found.")
        return
    
    # validate user with password
    password = input("Enter your password to verify your identity.")
    if check_credentials(uid, password):
        print("Password varified. You will now input updated user information.")
        pass
    else:
        print("Invalid password.")
        return
    
    # create new User attributes
    newname = input("Enter your name.")
    newuid = input("Input a user ID. It can be a new one if you'd like.")
    check = find_by_uid(newuid)
    if (check != "None") and (check != uid):
        print(f"The user ID {newuid} is already being used by another user.")
        return
    newps = input("Input a password. It can be a new one if you'd like.")
    newdob = input("Enter your date of birth in 'YYYY-MM-DD' format.")
    try:
        dobconv = datetime.strptime(newdob, '%Y-%m-%d').date()
    except ValueError:
        dobconv = datetime.today()
        print(f"Invalid date {newdob}: incorrect YYYY-mm-dd format. Date defaulted to {dobconv}")
           
    # update the user in the database
    with app.app_context():
        try:
            object = user.update(name=newname, uid=newuid, password=newps, dob=dobconv)
            print("Updated user:\n", object.read())
        except:  # error raised if object not created
            print("Unknown error.")
        
update()

Found user with user ID "kkcbal".
Password varified. You will now input updated user information.
Updated user:
 {'id': 7, 'name': 'AJ Ruiz', 'uid': 'kkcbal', 'dob': '05-18-2006', 'age': 16}

Delete Function

Below is a function that allows for the deletion of a certain user if they verify their user ID and password.

def delete():
    # first require uid input
    uid = input("Enter your user id:")
    user = find_by_uid(uid)
    if user != None:
        print('Found user with user ID "' + uid + '".')
        pass
    else:
        print("User not found.")
        return
    
    # validate user with password
    password = input("Enter your password to verify your identity.")
    if check_credentials(uid, password):
        print('Password varified. User with ID "' + uid + '" will be deleted...')
        pass
    else:
        print("Invalid password.")
        return
    
    with app.app_context():
        try:
            rslt = user.delete()
            print("User has been deleted successfully.")
        except:
            print("There was an unknown error deleting the given user.")

delete()

Found user with user ID "lex".
Password varified. User with ID "lex" will be deleted...
User has been deleted successfully.

I decided to delete the user Alexander Graham Bell for an example. After running all of the above processes, the SQLite table looks like this: