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: The project that we did last trimester is an example of where I saw this type of code2. SQLAlchemy object: After inputting the data we would use SQLSalchemy for the SQLite table that would have all the data that we inputted stored.
"""
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: it creates an object that has attributes- db.Model inheritance: Db.model inherits is a parameter of class user
  • init method: Initializes the program and it is the constructor.
  • @property, @.setter:</strong> This is the setter and getter method where you can get data (for the getter) and you can change or update or create (wich is the setter)</li>
  • additional methods: Update and delete methods
  • </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.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: The values that are inputted get stored and are added in the SQLite table2. User Object Constructors: the Init method?
    2. Try / Except: IF there is an error, it will go to the except method, but there isn't then it just runs the program.
    """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.
    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
    2. user.password
    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
    2. user = User(...)
    3. user.dob and try/except
    4. user.create() and try/except
    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': '', 'uid': '123sri', 'dob': '12-12-2005', 'age': 17}
    
    def update():
        # optimize user time to see if uid exists
        uid = input("Enter your user id:")
        user = find_by_uid(uid)
        if user is None:
            print(f"User with ID {uid} not found")
            return
        
        # request value that ensure creating valid object
        name = input("Enter your name:")
        password = input("Enter your password")
        
        # Initialize User object before date
        updated_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:
            updated_user.dob = datetime.strptime(dob, '%Y-%m-%d').date()
        except ValueError:
           updated_user.dob = datetime.today()
           print(f"Invalid date {dob} require YYYY-mm-dd")
               
        # write object to database
        with app.app_context():
            try:
                updated_user.update()
                print(f"User with ID {uid} updated successfully")
            except:  # error raised if object not created
                print(f"Error updating user with ID {uid}")
            
    update()
    
    User with ID srik123 not found
    
    def delete():
        # optimize user time to see if uid exists
        uid = input("Enter user ID to delete:")
        user = find_by_uid(uid)
        if user is None:
            print(f"User with ID {uid} not found")
            return
        
        # delete object from database
        with app.app_context():
            try:
                user.delete()
                print(f"User with ID {uid} deleted successfully")
            except:
                print(f"Error deleting user with ID {uid}")
    delete()
    
    User with ID srik123 not found
    

    Reading users table in sqlite.db

    Uses SQLALchemy query.all method to read data

    • Comment on purpose of following
    1. User.query.all
    2. json_ready assignment
    # 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': '03-20-2023',
      'age': 0},
     {'id': 3,
      'name': 'Alexander Graham Bell',
      'uid': 'lex',
      'dob': '03-20-2023',
      'age': 0},
     {'id': 4,
      'name': 'Eli Whitney',
      'uid': 'whit',
      'dob': '03-20-2023',
      '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': '', 'uid': '123sri', 'dob': '12-12-2005', 'age': 17}]

    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>