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.
-
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
Imports and Flask Objects
Defines and key object creations
- Comment on where you have observed these working? Provide a defintion of purpose.
- Flask app object. I observe flask app object on anything that runs locally such as my local site or locally running my project from last trimester.
- SQLAlchemy db object. I observe SQLAlchemy for any database table that holds table such as fitness data from my project last trimester.
"""
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, purpose and defintion.
- class User:Class is a templete definition for the property user - db.Model inheritanceThis defines the database and what is inside of it
- init method: Helps initialize attributes of the objects created.
-
@property,@<column>.setterSetter changes the value that was initialized - create, read, update, delete methods: Common methods for databasing. Methods to help us interact with data and interact with CRUD.
""" 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.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. Uses a ORM tool in order to create the tables.
- Create All Tables from db Object:Automates the creation of database tables using an ORM tool. 2. User Object Constructors: Creates different ways to create a user class with different attributes. User Object Constructors: Enables creating objects of the User class with different attributes using different constructors.
- Try / Except: Creates exceptions for errors so the site doesn't crash. Try / Except: Prevents the site from crashing by handling errors and exceptions in code execution.
"""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 User.query.filter_by:Used to query the database to find rows in the User table that match certain conditions specified in the filter_by function. This is a common way of retrieving data from a database using an ORM. 2. user.password user.password: Refers to the password property of the user object, which is typically used for authentication and security purposes. This property stores the password for the user, often in an encrypted or hashed format to protect it from unauthorized access.
ORM(Oject Relational Model)- in SQLALCHEMY ORM
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 The purpose of user.find_by_uid() is to find a user by their unique identifier (uid). The try/except block is used to handle the case where the user with the given uid does not exist in the system.
- user = User(...) The purpose of this statement is to create a new user object and assign it to the variable user. The ellipsis (...) represents the arguments that are passed to the constructor of the User class.
- user.dob and try/except The purpose of user.dob is to access the date of birth property of the user object. The try/except block is used to handle the case where the date of birth is not available or cannot be retrieved for some reason.
- user.create() and try/except The purpose of user.create() is to create a new user in the system. The try/except block is used to handle errors that might occur during the creation process, such as problems connecting to the database or missing/invalid required fields
adding a username and password
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 The purpose of User.query.all is to query the database for all instances of the User model and return them as a list.
- json_ready assignment, google List Comprehension The purpose of this code is to convert a list of User objects into a list of dictionaries that are ready to be serialized into JSON format. This is achieved using a list comprehension, which is a concise way to create a new list by applying a transformation to each element of an existing list. In this case, the transformation is to call the to_dict method on each User object to convert it to a dictionary representation. The resulting list of dictionaries can then be serialized into JSON format using a JSON library.
# 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()