Unit 2.4a Using Programs with Data, SQLAlchemy
Using Programs with Data is focused on SQL and database actions. Part A focuses on SQLAlchemy and an OOP programming style,
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.
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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 databaseapp.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 class that manages the actions in the 'users' table
- db.Model inheritance It is a parameter of class User Object oriented programming
- init method Is the constructor for the class User Initializes the instance variables within object
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@property,@<column>.setter@property is a getter method that extracts from the object @.setter allows the variable that was created to be updated</li> - create, read, update, delete methods Allows the database and specific data inside to be created, read, updated, and deleted
</ul> </li> </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 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.add(self) # performs update when id exists db.session.commit() return self # CRUD delete: remove self # None def delete(self): db.session.delete(self) db.session.commit() return None
"""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()
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 Allows the database and specific data inside to be created, read, updated, and deleted
- user.password If the uid is found, the passwords are checks and verified to make sure the password exists and is correct.
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 A uid is inputted and it is checked whether the uid exists or not If the user is found, then nothing is created If there is no user with that uid, a new user is created
- user = User(...) This only runs if the user is not found A new user is created using the class User with a name, uid, and password
- user.dob and try/except This only runs if the user is not found If the dob that is inputted is the same as the date today, then an error appears
- user.create() and try/except This only runs if the user is not found If the object is not created, an error is raised; otherwise, the user is created
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()
Reading users table in sqlite.db
Uses SQLALchemy query.all method to read data
- Comment on purpose of following
- User.query.all This gets all the users from the database
- json_ready assignment, google List Comprehension This reads all the users from the table and places them in a list using list comprehension Each are turned into JSON data
# 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()
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()
</div>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()