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
Imports and Flask Objects
Defines and key object creations
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Comment on where you have observed these working? Provide a definition of purpose.
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Flask app object
This object allows the app to know its location and set up paths.
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SQLAlchemy db object
This object creates the database that stores and organized data in a table format.
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"""
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 User uses the database model to create a new user using the attributes from this model. A user that is created is an object of this User class. - db.Model inheritance: This suggests that every user "inherits" the qualities present in the User class. These qualities include a name, id, uid, password, and dob.
- init method: The init method initializes the instance variables or attributes within an object.
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@property,@<column>.setter: Setters and getters protect your data when you create a class. A getter method returns an attribute's value, while a setter method sets or updates the attribute's value. - create, read, update, delete methods: These are the CRUD operations that allow you to change data by creating new data, reading existing data, updating existing data, and deleting existing data.
""" 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
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 create_all function creates a new table into the database. 2. User Object Constructors: These create an object with the inputs inputted by the user.
- Try / Except: The code tries something and if it doesn't work and returns an error, the code goes to the except block which handles the error (usually displays that an error occurred).
"""Database Creation and Testing """
# creates database entries/users
# 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:This is used to filter the database entries by a certain attributes. In this case, the entries are filtered by uid. 2. user.is_password: This function verifies if the password matches the password stored in the database.
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:If an entry is found with the uid of the one as the parameter in the find_by_uid function. If no entry is found, program proceeds past the function. 2. user = User(...): This sets the attributes (listed in the User class) inputted by the user as a variable called user.
- user.dob and try/except: This sets the date of birth of the object from the user class created by the user as they provide input for the different attributes. If the date provided by the user is valid, this is set as the dob of the user object. If not, the user's dob is set to the current date and an invalid date message is displayed.
- user.create() and try/except: This function adds a new entry to the database with the new user object. This happens in the try block. If this fails, the program proceeds to the except block where an error message is displayed to the user.
# Inputs, Try/Except, and SQLAlchemy work together to build a valid database object
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() # Calling create function
Reading users table in sqlite.db
Uses SQLALchemy query.all method to read data
- Comment on purpose of following
- User.query.all:This function extracts all entries from the database. The variable table stores a list of the users. 2. json_ready assignment, google List Comprehension: The users and converted into JSON format and are stored into the variable json_ready.
# 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() # Calling read function
# # Inputs, Try/Except, and SQLAlchemy work together to update a valid database object
# def updateByUid():
# # optimize user time to see if uid exists
# uid = input("Enter your user id:")
# # 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
# )
# # update 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}")
# dictionary = {
# "uid": uid,
# "inputs": {"uid": uid, "name": name, "password": password, "dob": dob}
# }
# uid1 = input("Enter the uid for the entry you want to update.")
# data = dictionary.get('inputs') # get what needs to be updated
# entry = find_by_uid(uid1) # get the uid
# print(entry)
# with app.app_context():
# entry.update(data)
# db.session.commit() # save the changes to the database
# return f" The user with the uid {entry.uid1} has been updated."
# updateByUid() # Calling update function
def updateByUid():
# input - uid of the user which we want to update
uid = input("Enter the user id for the user you want to update.")
user = find_by_uid(uid)
if user == None:
print("User does not exist.")
return
else:
print('User Found With user id '+uid)
newUid = input("Enter a new Uid")
newName = input("Enter a new name")
# Update the user details
with app.app_context():
try:
object = user.update(name=newName, uid=newUid)
print("User is successfully updated: ", object.read())
except:
print("Error Occurred: User not updated")
updateByUid()
def deleteByUid():
with app.app_context():
uid = str(input("Enter the uid of the entry you want to delete."))
entry = find_by_uid(uid)
if entry == None:
print("UID not found.")
return
entry.delete()
return f"The user with the uid {entry.uid} has been deleted."
deleteByUid() # Calling delete function