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.
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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'
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
- class User purpose - The object assigned to the user's purpose
- db.Model inheritance - A parameter of class user, it is being inherited; object-oriented programming
- init method - The method used to initialize the database
- @property, @
.setter - Getter and setter; gets, updates, and reads data between a frontend/backend</li> - additional methods - object vs integrational programming
</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?
- Create All Tables from db Object
- creates the tables/database according to the information input by the user
- User Object Constructors
- Constructs a User as an object, based on the input data
- Try / Except
- Tells program to try a command, skips to except command if try is not met (a lot like elif)
"""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
- Finds user id by using attributes
- Runs a check to make sure the id is the same as what is input
- Object used to find other object
- user.password
- creates a password and checks it to make sure it exists
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
- Finds user based on the number in the UID, ensures that the user is there or does a pass if it isn't
- user = User(...)
- The user information, initializes user so it can be pulled up
- user.dob and try/except
- If a birthdate is input, it runs try, if no birthdate is input, it runs except
- user.create() and try/except
- creates user based on the information that is input
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()
# 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()
def update(): uid = input("Enter your user id:") user = find_by_uid(uid) if (user is None): print("User ", uid, " NOT found\n") return else: print("User ", uid, " found\n", user.read()) newName = input("Update your name or click enter to move to the 1next item.") if newName != "": user.name = newName print("New name cannot be the old name.") else: pass newPassword = input("Update your password or click enter to move to the next item.") if newPassword != "": user.password = newPassword print("New password cannot be the old password.") else: pass newDob = input("Update your date of birth using 'YYYY-MM-DD'or click enter to move to the next item.") if newDob != "": user.dob = newDob print("New date of birth cannot be the old date of birth.") else: pass # write object to database with app.app_context(): try: object = user.update() print("Created\n", object.read()) except: # error raised if object not created print("Unknown error uid {uid}") update()
def delete(): uid = input("Enter your user id:") user = find_by_uid(uid) try: print("Found\n", user.read()) except: print("User not found.") with app.app_context(): try: object = user.delete() print("User deleted.") except: # error raised if object not created print("Unknown error uid {uid}") if object == None: print("User deleted successfully.") else: print("Error") delete()
Answers, Notes, etc.
- class User purpose - The object assigned to the user's purpose
- db.Model inheritance - A parameter of class user, it is being inherited; object-oriented programming
- init method - The method used to initialize the database
- @property, @
.setter - Getter and setter; gets, updates, and reads data between a frontend/backend</li> - additional methods - object vs integrational programming
</ul>- What is a database schema?
- A blueprint that describes how a database is organized.
- What is the purpose of identity Column in SQL database?
- Differentiation between different columns
- What is the purpose of a primary key in SQL database?
- The ID of the database; how the table can be accessed.
- What are the Data Types in SQL table?
- Integers, strings, bullions, images.