Unit 2.4a Using Programs with Data, SQLAlchemy
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.
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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"
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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
"""
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'
# SQLAlchemy object
db = SQLAlchemy()
# This belongs in place where it runs once per project
#Flask app object
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
- db.Model inheritance
- init method
- @property, @
.setter</li> - additional 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): # -- defining the template for users, used to create objects, users assign attributes into these templates, class is a template for future object # -- inherit the capability to make the class use the database properties, methods, attributes __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) # -- adding to the template database information # constructor of a User object, initializes the instance variables within object (self) def __init__(self, name, uid, password="123qwerty", dob=datetime.today()): # -- 123qwerty is the default if new data is not given # --the innit method is called "the constructor", it is used to instantiate (make, create) an object from our user class 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)) # the crud is the additional methods that are use in a class to create read update and delete # 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 # setter used to add data to object # getter (property) used to retrieve data from an object
"""Database Creation and Testing """ # Builds working data for testing def initUsers(): with app.app_context(): """Create database and tables""" db.create_all() # this is using the create function to add all users to the database """Tester data for table""" """these attributes make the u1 object""" 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: # tests for errors try: '''add user to table''' object = user.create() print(f"Created new uid {object.uid}") #handles the errors except: # error raised if object nit created '''fails with bad or duplicate data''' print(f"Records exist uid {user.uid}, or error.") # this constructs the users and adds them to the object initUsers()
def find_by_uid(uid): with app.app_context(): # it looks for the uid of a specific user 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 # verifying if the password is the right password from that user if (user.is_password(password)): return True return False # check_credentials("indi", "123qwerty")
def create(): # optimize user time to see if uid exists uid = input("Enter your user id:") # finds the uid and checks it it exists in database user = find_by_uid(uid) # if it does exist, it will print the existing one try: print("Found\n", user.read()) return # if it doesn't exist it will keep executing the following code 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 # it calls the stuff in the user object 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: # it creates/ adds this new user to the database object = user.create() print("Created\n", object.read()) except: # error raised if object not created print("Unknown error uid {uid}") create()
# SQLAlchemy extracts all users from database, turns each user into JSON def read(): with app.app_context(): # it gets all the data from the database table = User.query.all() # creates a list of JSON strings to store in database. json_ready = [user.read() for user in table] # each user adds user.read() to list return json_ready # read()
def delete(): # get uid of user to delete uid = input("Enter the uid of the user you want to delete: ") user = find_by_uid(uid) # check if user exists if user is None: print(f"No user found with uid {uid}") return # delete user from database with app.app_context(): try: user.delete() print(f"User {uid} deleted") except: print("Unknown error occurred during deletion") delete()
def update(): # get uid of user to update uid = input("Enter the uid of the user you want to update: ") user = find_by_uid(uid) # check if user exists if user is None: print(f"No user found with uid {uid}") return # print current user information print("Current user information:") print(user.read()) # request updated information name = input("Enter updated name (press enter to keep current value): ") if name: user.name = name password = input("Enter updated password (press enter to keep current value): ") if password: user.password = password dob = input("Enter updated date of birth (YYYY-MM-DD) (press enter to keep current value): ") if dob: try: user.dob = datetime.strptime(dob, '%Y-%m-%d').date() except ValueError: print(f"Invalid date {dob} require YYYY-mm-dd, date not updated") # update user in database with app.app_context(): try: user.update() print(f"User {uid} updated") print(user.read()) except: print("Unknown error occurred during update") update()
</div>Hacks
- Add this Blog to you own Blogging site. In the Blog add notes and observations on each code cell.
- In this implementation, do you see procedural abstraction?
- In 2.4a or 2.4b lecture
- Do you see data abstraction? Complement this with Debugging example.
- Use Imperative or OOP style to Create a new Table or do something that applies to your CPT project.
Reference... sqlite documentation