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?
  1. Flask app object Used this as an api for project last tri
  2. SQLAlchemy object Used this to create access data from sqlite table.
"""
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 purposeClass user marks all of the characteristics of the class and what factors are included in that class

  • db.Model inheritance db.model is being inherited by the user. db.model is being but into user, so the db.model functions like column can be used, through inheritcance we can use different functions and create sqlite table
  • init method sets up the attributes of the class
  • @property, @.setter getter is equivalent to read, and setter is equivalent to update/create. These are properites.</li>
  • additional methods create, read, update methods within the user itself.
  • </ul> </div> </div> </div>
    """ 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=""):
            """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.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?
    1. Create All Tables from db Object db Object is organized in a structured manner. Create All tables allows the creation of the table. Later it can be populated with user inputed data.
    2. User Object Constructors By defining all methods of the user object in the constructor, the model users is consistent and can be used many times throughout the applications.
    3. Try / Except Accounts for an error. Returns None if error getting the data occurs.
    """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()
    
    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.
    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
    1. User.query.filter_by

      filters by the parameter set, in this case uid

    2. user.password Checks if passwor
    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 used to retrience a user object by its unique identifier, uid. Uses try and expect to handle error
    2. user = User(...) used to make a new 'User' object with appropriate parameters and to first populate the table. Uses try and expect to handle error
    3. user.dob and try/except used to retrience a user object by date of birth property of user object . Uses try and expect to handle error
    4. user.create() and try/except used to add a new user object to database. Uses try and expect to handle error
    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.dbo}")
               
        # 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': 'Tanisha Patil', 'uid': 'tanisha', 'dob': '09-03-2007', '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 Retrieves all instances of a particular table from a databse using SQLAlchemy
    2. json_ready assignment Prepares a python object or datastructure to be put into json format
    # 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': 'Tanisha Patil',
      'uid': 'tanisha',
      'dob': '09-03-2007',
      'age': 15}]

    Delete and Update Functions

    def delete_by_uid(): 
        uid = input("Enter uid of user to be deleted.")
        user = find_by_uid(uid)  # using previous function to locate user by inputted id
        with app.app_context():
            try:
                object = user.delete() 
                print(f"User with uid --{uid}-- has been deleted. ")
                db = read()
                print(db)
            except:  # error raised if object not found
               (f"No user with uid {uid} was found.")
            
    delete_by_uid()
    
    User with uid --tanisha-- has been deleted. 
    [{'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}]
    
    def update_user():
        uid = input("Enter uid of user to be updated")
        user = find_by_uid(uid)
        name = input("Enter new name:")
        password = input("Enter new password:")
        with app.app_context():
            try:
                object = user.update(name=name,uid=uid, password=password) 
                print(f"User with uid --{uid}-- has been updated: {object} ")
            except:  # error raised if object not found
               (f"No user with uid {uid} was found.")
        db = read()
        print("---Updated db:---")
        print(db)
    update_user()
    
    User with uid --indi-- has been updated: {"id": 5, "name": "Mr. Jones", "uid": "indi", "dob": "10-21-1920", "age": 102} 
    ---Updated db:---
    [{'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': 'Mr. Jones', 'uid': 'indi', 'dob': '10-21-1920', 'age': 102}, {'id': 6, 'name': 'Marion Ravenwood', 'uid': 'raven', 'dob': '10-21-1921', 'age': 101}]
    

    Hacks

    • Add this Blog to you own Blogging site. In the Blog add notes and observations on each code cell.
    • Add Update functionality to this blog.
    • Add Delete functionality to this blog.
    </div>