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 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 - Template definition for the property 'User'
- db.Model inheritance - db.Model holds additional properties which enables us to make this into a table & makes 'user' template usable for database stuff
- init method - Init method receives parameters and makes the user
-
@property,@<column>.setter- setters and getters allow you to see or change the values inside attributes of your object - create, read, update, delete methods - CRUD lets you manipulate data in the database
""" 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): # Template definition for the property 'User'
# db.Model holds additional properties which enables us to make this into a table
# makes 'user' template usable for database stuff
__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)
# Init method receives parameters and makes the user
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
# setters and getters allow you to see or change the values inside attributes of your object
# 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 lets you manipulate data in the database
# 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
"""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"""
# Input data for objects which are made from the template defined by 'User'
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()
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")
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()
# 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()
"""
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)
""" database dependencies to support sqlite examples """
import json
from sqlalchemy.exc import IntegrityError
from werkzeug.security import generate_password_hash, check_password_hash
class Player(db.Model):
__tablename__ = 'NBA' # 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)
_points = db.Column(db.Integer, unique=False, nullable=False)
_assists = db.Column(db.Integer, unique=False, nullable=False)
_rebounds = db.Column(db.Integer, unique=False, nullable=False)
# constructor of a User object, initializes the instance variables within object (self)
# Init method receives parameters and makes the user
def __init__(self, name, points, assists, rebounds):
self._name = name # variables with self prefix become part of the object,
self._points = points
self._assists = assists
self._rebounds = rebounds
# setters and getters allow you to see or change the values inside attributes of your object
# 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 points from object
@property
def points(self):
return self._points
# a setter function, allows points to be updated after initial object creation
@points.setter
def points(self, points):
self._points = points
# an assists getter method, extracts name from object
@property
def assists(self):
return self._assists
# a setter function, allows assists to be updated after initial object creation
@assists.setter
def assists(self, assists):
self._assists = assists
# a rebound getter method, extracts name from object
@property
def rebounds(self):
return self._rebounds
# a setter function, allows rebounds to be updated after initial object creation
@rebounds.setter
def rebounds(self, rebounds):
self._rebounds = rebounds
# 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 lets you manipulate data in the database
# 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,
"points": self.points,
"assists": self.assists,
"rebounds": self.rebounds
}
# CRUD update
# returns self
def update(self, dictionary):
"""only updates values with length"""
print(f"Before update: {self.read()}")
for key in dictionary:
if key == "points":
self.points = dictionary[key]
if key == "assists":
self.assists = dictionary[key]
if key == "rebounds":
self.rebounds = dictionary[key]
db.session.merge(self)
db.session.commit()
print(f"After update: {self.read()}")
return None
# 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 initPlayers():
with app.app_context():
"""Create database and tables"""
db.create_all()
"""Tester data for table"""
# Input data for objects which are made from the template defined by 'User'
p1 = Player(name='Stephen Curry', points='25', assists='7', rebounds='5')
p2 = Player(name='LeBron James', points='27', assists='7', rebounds='8')
p3 = Player(name='Michael Jordan', points='30', assists='5', rebounds='6')
p4 = Player(name='Magic Johnson', points='19', assists='11', rebounds='7')
players = [p1, p2, p3, p4]
"""Builds sample player/note(s) data"""
for p in players:
try:
'''add user to table'''
object = p.create()
print(f"Created new player {object.name}")
except: # error raised if object not created
'''fails with bad or duplicate data'''
print(f"Records exist name {p.name}, or error.")
initPlayers()
def create():
# optimize user time to see if uid exists
name = input("Enter your player name")
player = find_by_name(name)
try:
print("Found\n", player.read())
return
except:
pass # keep going
points = input("Enter your number of points")
assists = input("Enter your number of assists")
rebounds = input("Enter your number of rebounds")
# Initialize User object before date
player = Player(name=name,
points=points,
assists=assists,
rebounds=rebounds
)
# write object to database
with app.app_context():
try:
object = player.create()
print("Created\n", object.read())
except: # error raised if object not created
print("Unknown error name {name}")
create()
def read():
with app.app_context():
table = Player.query.all()
for player in table:
print(player)
read()
def put():
name = str(input("Enter the name of the player you want to edit"))
pts = int(input("Enter the player's new amount of points."))
ast = int(input("Enter the player's new amount of assists."))
reb = int(input("Enter the player's new amount of rebounds."))
body = {
"name": name,
"data": {"points": pts, "assists": ast, "rebounds": reb}
}
data = body.get('data') # get what needs to be updated
player = find_by_name(name) # get the player (using the name in this case)
with app.app_context():
player.update(data)
db.session.commit() # save the changes to the database
return f"{player.name} at id {player.id} has been updated"
put()
read()