Using Programs with Data and SQLAlchemy
This is the first lesson that talks about using programs with Data and SQLAlchemy based around Big Idea 2.4
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? TRI 2 FINAL PROJECT
-
Flask app object
- I have seen us using the Flask App Object in our Trimester 2 Final Project and some in our Trimester 1 Project. We have used flask app objects as APIs from trimesters 1 and 2. We can register new blueprints, which is important for us in order to create our API connecting the frontend and backend together.
-
SQLAlchemy object
- We have used the db object in order to create our database from last trimester. When we set db equal to the SQLAlchemy object, we were registering our database, which made the table full of our data. We have used it in an assignment to get familiar with it before
"""
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 databaseapp.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 of this is to create a new person with its different characteristics. It works the same way as the class User is going to include multiple attributes, such as their user id, their date of birth, age, and more.
-
db.Model inheritance
- Our class has a db.model. Defining a class is called inheritance and we are going to inherit the ability for our database to use database properties and attributes. We are making our class using the database properties and using multiple different areas of data
-
init method
- This is often called the constructor
- Used to help instantiate an object from the user class
- The init() method is what constructs the User object, which initializes the instance variables within the object
- @property, @
.setter - The @property and @setter methods are getter and setter functions, respectively, that allow the attributes to be accessed and updated.
- additional methods, CRUD, Create, Read, Update, Delete
</ul> </div> </div> </div>- The create(), read(), update(), and delete() methods all implement the CRUD (Create, Read, Update, Delete) operations for the 'users' table
- The create() method adds a new user object to the table, the read() method outputs a dictionary representation of the user object, the update() method updates the attributes of the user object (includes before and after), and the delete() method removes the user object from the table
""" 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.add(self) # performs update when id exists\n", 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 "db.create_all" line makes the table that is defined in the database schema with the SQLAlchemy. It reads the schema and creates the tables in the connected database
- User Object Constructors
- The code creates instances of the User class using the constructor with different combinations of arguments, such as name, uid, password, and date of birth. It will sort the data that each user uses. It initializes these instances as u1, u2, u3, u4, u5, and u6.
- Try / Except
- The try/except lines makes a new row in the User table with the data passed to the constructor. If the data is valid and the row is successfully created, create() will output the created User object. Otherwise, it raises an exception. The try/except block handles any exceptions that may occur during the creation process, such as duplicate user ids or other validation errors. An if statement is used to find out if something is already there
"""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 code shows that the user.query.filter_by is intended to distinguish a user by their user id, which allows one to know which id represents which user. The user can input a user id
- user.password
- The user.is_password checks the attributes of a user by finding and verifying the user's password. If te password found is the user's password, the boolean variable will evaluate to true. If the password found is not the user's password, the variable will be evaluated to false.
def find_by_uid(uid): with app.app_context(): user = User.query.filter_by(_uid=uid).first() return user # returns user object # def find_by_name(name): # with app.app_context(): # name = User.query.filter_by(_name=name).first() # return name # 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 # user2 = find_by_name(name) # if user2 == None: # return False # if (user2.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 user.find_by_uid(uid) method is used to check if a user with the given uid already exists in the database. The try/except block is used to handle the case when no user is found with the given uid. If user.read() is called when user is None, it will raise an AttributeError, so the try/except block is used to catch this error and continue with creating a new user.
- user = User(...)
- user = User(...) creates a new instance of the User class with the given attributes. It initializes a new User object with the name, uid, and password provided by the user through the input() method.
- user.dob and try/except
- user.dob sets the date of birth attribute for the User object. The try/except block is used to handle the case when the inputted date is invalid, for example, when the inputted date does not follow the format 'YYYY-MM-DD'. If the date is invalid, the current date is used instead and the user is informed that the date was invalid.
- user.create() and try/except
- user.create() method is a custom method that is used to add a new row to the database table for the given User object. The try/except block is used to catch any errors that may occur when creating the new row in the database. If any errors occur, the user is informed that an unknown error has occurred with the uid provided.
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()
Reading users table in sqlite.db
Uses SQLALchemy query.all method to read data
- Comment on purpose of following
- User.query.all
- User.query.all() is a method provided by SQLAlchemy to query (retrieve data from the database) all records in the User table. It returns a list of User objects that represent all the records in the table.
- json_ready assignment
- The json_ready variable is assigned a list of JSON objects that represent the records in the User table. The list is generated using a list comprehension, which is an efficient way of generating lists in Python. The list comprehension [user.read() for user in table] loops through each User object in the table list and calls the read() method on each object, which returns a JSON representation of the user. The resulting list of JSON objects is then assigned to the json_ready variable.
# 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 delete_by_uid(): # makes a new function called delete_by_uid uid = input("Enter uid of user to be deleted.") # prompts the user to enter the uid user = find_by_uid(uid) # using previous function to locate user by inputted id with app.app_context(): try: object = user.delete() print(f"User with uid --{uid}-- has been deleted. ") db = read() print(db) except: # error raised if object not found (f"No user with uid {uid} was found.") delete_by_uid()
</div>def user_update(): uid = input("Enter uid of user to be updated") # define variable uid so user inputs user = find_by_uid(uid) # calls the find_by_uid function name = input("Enter new name:") # prompts user to enter new name password = input("Enter new password:") # prompts user to enter the new password with app.app_context(): try: object = user.update(name=name,uid=uid, password=password) # change the table data of that user print(f"User with uid --{uid}-- has been updated: {object} ") # like console log, tells user it has been updated except: # error raised if object not found (f"No user with uid {uid} was found.") # If user inputs a uid that is not there, it will show this db = read() # calls the read function print("---Updated db:---") print(db) user_update() # calls the user_update function