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
      1. I saw the Flask app object in our CPT project, where it managed many if not all operations that we wanted to perform with flask
    2. SQLAlchemy db object
      1. The db object was also created in our CPT project, where it was used to establish a connection and perform database operatoins and manipulations on our 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)

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 creates an abstractiion for our User, and contains all the attributes of the user (info such as uid and name) to potential methods such as create, add delete and update. It serves the purpose of containing all of our necessary operations and information under one name, which we can use to easily edit users and update their entry later on in our program.
    • db.Model inheritance
      • This inherits all the methods and attributes from the db.Model class. Doing this enables us to use datatypes for our DB schema along with the other operations for CRUD
    • init method
      • This is our class constructor, it serves to instantiate the attributes of our user upon the creation of our object, and then allows us to use this data later on in our operations
    • @property, @<column>.setter
      • These decorators are used to establish the getters and setters within a class or object, it serves to create references for us to use to reference clas methods and attributes outside of the class
    • create, read, update, delete methods
      • These are certain data base operations that we can use to edit, access, and retrieve data from our database. We can achieve this through OOP with SQLAlchemy, or imperatively with sqlite3

  • Methods are used to help to solve problems with a class

""" 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):  # Inherits from db.Model, allows for our User to not only be used as an Object to store information, but also give it the ability to perform database operations.
    __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()): # This is the class constructor, it initializes our values within the class. In python __init__() is used to instantiate an object
        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

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
      1. calls the create_all() method from the db object created in the model class. I assume that takes the Object properties and generates the table with the object entries.
    2. User Object Constructors
      1. defined with __init__(), takes in the inputted data and assigns it to class variables for future operations such as adding to database.
    3. Try / Except
      1. Attempts a specific database operation. If it works, do nothing. If it fails, remove the current session to prevent futhur errors. 
"""Database Creation and Testing """


# Builds working data for testing
def initUsers():
    with app.app_context():
        """Creatte 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()

Records exist uid toby, or error.
Records exist uid niko, or error.
Records exist uid lex, or error.
Records exist uid whit, or error.
Records exist uid indi, or error.
Records exist uid raven, or error.

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
      1. Locates the first entry in the database where the value of the _uid coloumn is equal to a specific UID. Used to search for the object of a user to update.
    2. user.password
      1. accesses the password of the user.

  • ORM (Object Relational Mapping)

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
    1. user.find_by_uid() and try/except
      1. Locates and stores the object of the user in question. Try printing the user information to check if the user has been created, if NotFound error, we continue with the rest of the function
    2. user = User(...)
      1. Creates the user object with the inputted parameters
    3. user.dob and try/except
      1. Set the date of birth of our user. Try to format the date into a standard format, if an invalid input is detected, autofill with today's date
    4. user.create() and try/except
      1. creates the user object instantiated in the create() function with it's method in the Model class. This inserts our object into the database. 
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': 8, 'name': 'Jonah', 'uid': '4567', 'dob': '08-12-2007', 'age': 15}

Reading users table in sqlite.db

Uses SQLALchemy query.all method to read data

  • Comment on purpose of following
    1. User.query.all
      1. Grabs a list/iterable of all user entries in the database provided
    2. json_ready assignment, google List Comprehension
      1. Json formatted data. Uses list comprehension which takes all data from a prexisting list and moifies it to a copy that we later use.
# 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()

[{'id': 1,
  'name': 'Thomas Edison',
  'uid': 'toby',
  'dob': '02-11-1847',
  'age': 176},
 {'id': 2,
  'name': 'Nikola Tesla',
  'uid': 'niko',
  'dob': '03-19-2023',
  'age': 0},
 {'id': 3,
  'name': 'Alexander Graham Bell',
  'uid': 'lex',
  'dob': '03-19-2023',
  'age': 0},
 {'id': 4,
  'name': 'Eli Whitney',
  'uid': 'whit',
  'dob': '03-19-2023',
  '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': 'alex', 'uid': '1', 'dob': '03-19-2023', 'age': 0},
 {'id': 8, 'name': 'Jonah', 'uid': '4567', 'dob': '08-12-2007', 'age': 15}]
def update():
    uid = input("What user ID would you like to update?")
    user = find_by_uid(uid) # "List Comprehensions", for each user add user.read() to list
    name = input("Enter desired new name: ")
    uid = input("Enter desired new id: ")
    new_password = input("Enter desired new password: ")
    with app.app_context():
        try:
            object = user.update(name, uid, new_password)   
            print("Updated\n", object.read())
        except:  # error raised if object not created
            print("Unknown error uid {uid}")
    return

update()

Updated
 {'id': 8, 'name': 'Jonahs', 'uid': '4567', 'dob': '08-12-2007', 'age': 15}

def delete():
    uid = input("What user ID would you like to delete?")
    user = find_by_uid(uid)
    with app.app_context():
        try:
            object = user.delete()  
            print("Deleted\n")
        except:  # error raised if object not created
            print("Unknown error uid {uid}")
    return

    db.session.delete(self)
    db.session.commit()
    return None

delete()

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.

Debugging

I've set three Breakpoints to analyze the code, 1 before initializing the database, 1 before creating a user, and 1 after creating a userobject Breakpoints

First Breakpoint

Initial Class and function variables
In this screenshot, I was able to see the already defined global class and function variables before creating the database. We can see the existance of our db object, as well as our instantiated flask application. Looking at the function variables, we also see the imported methods for generating and checking password hashes from the werkzeug.security module. Knowing that the necessary modules, methods, and objects have been created, we can move on to the next breakpoint

Second Breakpoint

Class Variables of User objects
Local Variables
After creating a few users, we arrive at our next brekapoint. By now, we have already created a few users objects and instantiated their attributes and methods. By looking in the debug menu, we can see how any one of the objects contains the attributes that we defined in our Model object above. We can verify that we have the necessary data to procede to the final step of the init_users() function, where we continue to create the user entries in the database.

Third Breakpoint

Iteration
By now, we should've started creating the user entries within the database. We use an iterative method, and loop over each user within our users list to create each user. We can analyze the contents of this iteration through the debugging, where we see both the local user object instantiated by the loop and also the users list we are iterating over with.