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.
-
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?
- Flask app object:- Flask app object implements a WSGI(website server gateway interface) application which means it "calls forward requests". After you create it, it will be a central registry for view functions, the URL rules, template functions, etc. We have seen these working when building our databases last trimester and we get resources from other files for the jokes, users, etc.2. SQLAlchemy object:
- The SQLAlchemy object facilitates the communication between the database and the python programming. The cells that hold our databases like we did today, are converted to SQLAlchemy statements.
"""
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:The purpose is to provide a way to build the data and have everything work together. Within this there are the attributes like user id, name, etc.- db.Model inheritance: The User Class inherits from the db.model Then the different attributes like _name would be considered some of the columns in the user table.
- init method: Usually used to initialize attributes in a database. So when there is a new attribute in the database like the user id or whatever it is, the init method is used.
- @property, @
.setter: In databases setters and getters are used for the different attributes. These are used in python for the setters and getters.</li> - additional methods:
</ul> </div> </div> </div>- additional methods include crud methods. This stands for create, read, update, and delete. Each of these will obviously do something different but they all change or use the data base by adding, removing, reading, or updating.
""" 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
Class Notes:
- go to class user
- class definition is calld a template
- template definition- what porpertires wewant our users to have- for property user
- when we do u1 = user and send the properties, we make an object from the template definiition user
- we will make objects from the template
- db.model is how we inherit properties
- we defined it already in a db model
- we can do the column definitions
- enables our template user to be used as a way to create
- Now our user template can do database stuff
- init method recieves parameters and initializes attributes
- setters anfd getters, change attributes or retrieve these.
- properties and stuff
- command methods for databsing- added crud- help us interact with the data in our object
- we can have methods that help solve problems with the data
- we just defined the template
- ORM- on top of python that works with database
- Credentials check: query for the username and password
- first record that matches the user id
- check true and false, user and password true, user no password false, etc.
Initial Data
Uses SQLALchemy db.create_all() to initialize rows into sqlite.db
- Comment on how these work?
- Create All Tables from db Object
- the db Object is a template and a table will be included in this file.
- User Object Constructors
- A constructor is a special method that is called when an object is created from a class. We use the constructor init.
- Try / Except
- try and except blocks are used to handle exceptions and errors that may occur during the execution of your code.
"""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
- The purpose is to filter the users and when you check for the given credentials the user ids must be sorted through or filtered to make sure the uid is correct and specify the conditions.
- user.password
- The passwords in the table and data base are hashed. This creates higher levels of security.
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
- This has the purpose of finding a specific user id. Since the uid has to be unique, they are finding the user by the uid to determine them. It retrieves data.
- user = User(...)
- This has the purpose that creates an instance of the User model in a Flask application.
- user.dob and try/except
- This stores the date of birth of a user in a software application or program. The date of birth is a common piece of personal information used for identity verification and age verification purposes.
- user.create() and try/except
- It creates a new user with the attributes that you set for this new user. In terms of our database, a new row is added to the table.
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()
</div># 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()
- additional methods: