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"
  • 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.
    1. Flask app object
    2. SQLAlchemy db object
"""
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
    • db.Model inheritance
    • init method
    • @property, @<column>.setter
    • create, read, update, delete methods
""" 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?
    1. Create All Tables from db Object
    2. User Object Constructors
    3. Try / Except
"""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()
---------------------------------------------------------------------------
OperationalError                          Traceback (most recent call last)
File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/engine/base.py:3256, in Engine._wrap_pool_connect(self, fn, connection)
   3255 try:
-> 3256     return fn()
   3257 except dialect.dbapi.Error as e:

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/pool/base.py:310, in Pool.connect(self)
    303 """Return a DBAPI connection from the pool.
    304 
    305 The connection is instrumented such that when its
   (...)
    308 
    309 """
--> 310 return _ConnectionFairy._checkout(self)

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/pool/base.py:868, in _ConnectionFairy._checkout(cls, pool, threadconns, fairy)
    867 if not fairy:
--> 868     fairy = _ConnectionRecord.checkout(pool)
    870     fairy._pool = pool

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/pool/base.py:476, in _ConnectionRecord.checkout(cls, pool)
    474 @classmethod
    475 def checkout(cls, pool):
--> 476     rec = pool._do_get()
    477     try:

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/pool/impl.py:256, in NullPool._do_get(self)
    255 def _do_get(self):
--> 256     return self._create_connection()

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/pool/base.py:256, in Pool._create_connection(self)
    254 """Called by subclasses to create a new ConnectionRecord."""
--> 256 return _ConnectionRecord(self)

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/pool/base.py:371, in _ConnectionRecord.__init__(self, pool, connect)
    370 if connect:
--> 371     self.__connect()
    372 self.finalize_callback = deque()

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/pool/base.py:666, in _ConnectionRecord.__connect(self)
    665     with util.safe_reraise():
--> 666         pool.logger.debug("Error on connect(): %s", e)
    667 else:
    668     # in SQLAlchemy 1.4 the first_connect event is not used by
    669     # the engine, so this will usually not be set

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/util/langhelpers.py:70, in safe_reraise.__exit__(self, type_, value, traceback)
     69     if not self.warn_only:
---> 70         compat.raise_(
     71             exc_value,
     72             with_traceback=exc_tb,
     73         )
     74 else:

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/util/compat.py:207, in raise_(***failed resolving arguments***)
    206 try:
--> 207     raise exception
    208 finally:
    209     # credit to
    210     # https://cosmicpercolator.com/2016/01/13/exception-leaks-in-python-2-and-3/
    211     # as the __traceback__ object creates a cycle

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/pool/base.py:661, in _ConnectionRecord.__connect(self)
    660 self.starttime = time.time()
--> 661 self.dbapi_connection = connection = pool._invoke_creator(self)
    662 pool.logger.debug("Created new connection %r", connection)

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/engine/create.py:590, in create_engine.<locals>.connect(connection_record)
    589             return connection
--> 590 return dialect.connect(*cargs, **cparams)

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/engine/default.py:597, in DefaultDialect.connect(self, *cargs, **cparams)
    595 def connect(self, *cargs, **cparams):
    596     # inherits the docstring from interfaces.Dialect.connect
--> 597     return self.dbapi.connect(*cargs, **cparams)

OperationalError: unable to open database file

The above exception was the direct cause of the following exception:

OperationalError                          Traceback (most recent call last)
/home/user/vscode/APCSP/_notebooks/2023-03-13-AP-unit2-4a.ipynb Cell 8 in <cell line: 30>()
     <a href='vscode-notebook-cell://wsl%2Bubuntu-20.04/home/user/vscode/APCSP/_notebooks/2023-03-13-AP-unit2-4a.ipynb#X10sdnNjb2RlLXJlbW90ZQ%3D%3D?line=26'>27</a>                 '''fails with bad or duplicate data'''
     <a href='vscode-notebook-cell://wsl%2Bubuntu-20.04/home/user/vscode/APCSP/_notebooks/2023-03-13-AP-unit2-4a.ipynb#X10sdnNjb2RlLXJlbW90ZQ%3D%3D?line=27'>28</a>                 print(f"Records exist uid {user.uid}, or error.")
---> <a href='vscode-notebook-cell://wsl%2Bubuntu-20.04/home/user/vscode/APCSP/_notebooks/2023-03-13-AP-unit2-4a.ipynb#X10sdnNjb2RlLXJlbW90ZQ%3D%3D?line=29'>30</a> initUsers()

/home/user/vscode/APCSP/_notebooks/2023-03-13-AP-unit2-4a.ipynb Cell 8 in initUsers()
      <a href='vscode-notebook-cell://wsl%2Bubuntu-20.04/home/user/vscode/APCSP/_notebooks/2023-03-13-AP-unit2-4a.ipynb#X10sdnNjb2RlLXJlbW90ZQ%3D%3D?line=5'>6</a> with app.app_context():
      <a href='vscode-notebook-cell://wsl%2Bubuntu-20.04/home/user/vscode/APCSP/_notebooks/2023-03-13-AP-unit2-4a.ipynb#X10sdnNjb2RlLXJlbW90ZQ%3D%3D?line=6'>7</a>     """Create database and tables"""
----> <a href='vscode-notebook-cell://wsl%2Bubuntu-20.04/home/user/vscode/APCSP/_notebooks/2023-03-13-AP-unit2-4a.ipynb#X10sdnNjb2RlLXJlbW90ZQ%3D%3D?line=7'>8</a>     db.create_all()
      <a href='vscode-notebook-cell://wsl%2Bubuntu-20.04/home/user/vscode/APCSP/_notebooks/2023-03-13-AP-unit2-4a.ipynb#X10sdnNjb2RlLXJlbW90ZQ%3D%3D?line=8'>9</a>     """Tester data for table"""
     <a href='vscode-notebook-cell://wsl%2Bubuntu-20.04/home/user/vscode/APCSP/_notebooks/2023-03-13-AP-unit2-4a.ipynb#X10sdnNjb2RlLXJlbW90ZQ%3D%3D?line=9'>10</a>     u1 = User(name='Thomas Edison', uid='toby', password='123toby', dob=datetime(1847, 2, 11))

File ~/anaconda3/lib/python3.9/site-packages/flask_sqlalchemy/extension.py:868, in SQLAlchemy.create_all(self, bind_key)
    851 def create_all(self, bind_key: str | None | list[str | None] = "__all__") -> None:
    852     """Create tables that do not exist in the database by calling
    853     ``metadata.create_all()`` for all or some bind keys. This does not
    854     update existing tables, use a migration library for that.
   (...)
    866         Added the ``bind`` and ``app`` parameters.
    867     """
--> 868     self._call_for_binds(bind_key, "create_all")

File ~/anaconda3/lib/python3.9/site-packages/flask_sqlalchemy/extension.py:849, in SQLAlchemy._call_for_binds(self, bind_key, op_name)
    846     raise sa.exc.UnboundExecutionError(message) from None
    848 metadata = self.metadatas[key]
--> 849 getattr(metadata, op_name)(bind=engine)

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/sql/schema.py:4864, in MetaData.create_all(self, bind, tables, checkfirst)
   4862 if bind is None:
   4863     bind = _bind_or_error(self)
-> 4864 bind._run_ddl_visitor(
   4865     ddl.SchemaGenerator, self, checkfirst=checkfirst, tables=tables
   4866 )

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/engine/base.py:3122, in Engine._run_ddl_visitor(self, visitorcallable, element, **kwargs)
   3121 def _run_ddl_visitor(self, visitorcallable, element, **kwargs):
-> 3122     with self.begin() as conn:
   3123         conn._run_ddl_visitor(visitorcallable, element, **kwargs)

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/engine/base.py:3038, in Engine.begin(self, close_with_result)
   3036     conn = self.connect()
   3037 else:
-> 3038     conn = self.connect(close_with_result=close_with_result)
   3039 try:
   3040     trans = conn.begin()

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/engine/base.py:3210, in Engine.connect(self, close_with_result)
   3195 def connect(self, close_with_result=False):
   3196     """Return a new :class:`_engine.Connection` object.
   3197 
   3198     The :class:`_engine.Connection` object is a facade that uses a DBAPI
   (...)
   3207 
   3208     """
-> 3210     return self._connection_cls(self, close_with_result=close_with_result)

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/engine/base.py:96, in Connection.__init__(self, engine, connection, close_with_result, _branch_from, _execution_options, _dispatch, _has_events, _allow_revalidate)
     91     self._has_events = _branch_from._has_events
     92 else:
     93     self._dbapi_connection = (
     94         connection
     95         if connection is not None
---> 96         else engine.raw_connection()
     97     )
     99     self._transaction = self._nested_transaction = None
    100     self.__savepoint_seq = 0

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/engine/base.py:3289, in Engine.raw_connection(self, _connection)
   3267 def raw_connection(self, _connection=None):
   3268     """Return a "raw" DBAPI connection from the connection pool.
   3269 
   3270     The returned object is a proxied version of the DBAPI
   (...)
   3287 
   3288     """
-> 3289     return self._wrap_pool_connect(self.pool.connect, _connection)

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/engine/base.py:3259, in Engine._wrap_pool_connect(self, fn, connection)
   3257 except dialect.dbapi.Error as e:
   3258     if connection is None:
-> 3259         Connection._handle_dbapi_exception_noconnection(
   3260             e, dialect, self
   3261         )
   3262     else:
   3263         util.raise_(
   3264             sys.exc_info()[1], with_traceback=sys.exc_info()[2]
   3265         )

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/engine/base.py:2106, in Connection._handle_dbapi_exception_noconnection(cls, e, dialect, engine)
   2104     util.raise_(newraise, with_traceback=exc_info[2], from_=e)
   2105 elif should_wrap:
-> 2106     util.raise_(
   2107         sqlalchemy_exception, with_traceback=exc_info[2], from_=e
   2108     )
   2109 else:
   2110     util.raise_(exc_info[1], with_traceback=exc_info[2])

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/util/compat.py:207, in raise_(***failed resolving arguments***)
    204     exception.__cause__ = replace_context
    206 try:
--> 207     raise exception
    208 finally:
    209     # credit to
    210     # https://cosmicpercolator.com/2016/01/13/exception-leaks-in-python-2-and-3/
    211     # as the __traceback__ object creates a cycle
    212     del exception, replace_context, from_, with_traceback

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/engine/base.py:3256, in Engine._wrap_pool_connect(self, fn, connection)
   3254 dialect = self.dialect
   3255 try:
-> 3256     return fn()
   3257 except dialect.dbapi.Error as e:
   3258     if connection is None:

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/pool/base.py:310, in Pool.connect(self)
    302 def connect(self):
    303     """Return a DBAPI connection from the pool.
    304 
    305     The connection is instrumented such that when its
   (...)
    308 
    309     """
--> 310     return _ConnectionFairy._checkout(self)

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/pool/base.py:868, in _ConnectionFairy._checkout(cls, pool, threadconns, fairy)
    865 @classmethod
    866 def _checkout(cls, pool, threadconns=None, fairy=None):
    867     if not fairy:
--> 868         fairy = _ConnectionRecord.checkout(pool)
    870         fairy._pool = pool
    871         fairy._counter = 0

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/pool/base.py:476, in _ConnectionRecord.checkout(cls, pool)
    474 @classmethod
    475 def checkout(cls, pool):
--> 476     rec = pool._do_get()
    477     try:
    478         dbapi_connection = rec.get_connection()

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/pool/impl.py:256, in NullPool._do_get(self)
    255 def _do_get(self):
--> 256     return self._create_connection()

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/pool/base.py:256, in Pool._create_connection(self)
    253 def _create_connection(self):
    254     """Called by subclasses to create a new ConnectionRecord."""
--> 256     return _ConnectionRecord(self)

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/pool/base.py:371, in _ConnectionRecord.__init__(self, pool, connect)
    369 self.__pool = pool
    370 if connect:
--> 371     self.__connect()
    372 self.finalize_callback = deque()

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/pool/base.py:666, in _ConnectionRecord.__connect(self)
    664 except Exception as e:
    665     with util.safe_reraise():
--> 666         pool.logger.debug("Error on connect(): %s", e)
    667 else:
    668     # in SQLAlchemy 1.4 the first_connect event is not used by
    669     # the engine, so this will usually not be set
    670     if pool.dispatch.first_connect:

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/util/langhelpers.py:70, in safe_reraise.__exit__(self, type_, value, traceback)
     68     self._exc_info = None  # remove potential circular references
     69     if not self.warn_only:
---> 70         compat.raise_(
     71             exc_value,
     72             with_traceback=exc_tb,
     73         )
     74 else:
     75     if not compat.py3k and self._exc_info and self._exc_info[1]:
     76         # emulate Py3K's behavior of telling us when an exception
     77         # occurs in an exception handler.

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/util/compat.py:207, in raise_(***failed resolving arguments***)
    204     exception.__cause__ = replace_context
    206 try:
--> 207     raise exception
    208 finally:
    209     # credit to
    210     # https://cosmicpercolator.com/2016/01/13/exception-leaks-in-python-2-and-3/
    211     # as the __traceback__ object creates a cycle
    212     del exception, replace_context, from_, with_traceback

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/pool/base.py:661, in _ConnectionRecord.__connect(self)
    659 try:
    660     self.starttime = time.time()
--> 661     self.dbapi_connection = connection = pool._invoke_creator(self)
    662     pool.logger.debug("Created new connection %r", connection)
    663     self.fresh = True

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/engine/create.py:590, in create_engine.<locals>.connect(connection_record)
    588         if connection is not None:
    589             return connection
--> 590 return dialect.connect(*cargs, **cparams)

File ~/anaconda3/lib/python3.9/site-packages/sqlalchemy/engine/default.py:597, in DefaultDialect.connect(self, *cargs, **cparams)
    595 def connect(self, *cargs, **cparams):
    596     # inherits the docstring from interfaces.Dialect.connect
--> 597     return self.dbapi.connect(*cargs, **cparams)

OperationalError: (sqlite3.OperationalError) unable to open database file
(Background on this error at: https://sqlalche.me/e/14/e3q8)

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
    1. User.query.filter_by
    2. user.password
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
    1. user.find_by_uid() and try/except
    2. user = User(...)
    3. user.dob and try/except
    4. user.create() and try/except
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
    1. User.query.all
    2. json_ready assignment, google List Comprehension
# 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()

Hacks

  • Add this Blog to you own Blogging site. In the Blog add notes and observations on each code cell.
  • Change blog to your own database.
  • Add additional CRUD
    • Add Update functionality to this blog.
    • Add Delete functionality to this blog.