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• There will be an AssertionError when the assert condition does not meet.
• This does not mean that the program is buggy/vaulty.

• app.root_path refer to the root directory of the Python project.
• This notion comes from Python's os.path module. So, I need to import os at the start of the Python codes.

• It is a good idea to separate environmental settings and any other specific configuration files.
• Flask allows one to import these setting as a separate files later on if the settings is necessary.
• There is a method from_envvar() that is used to enable robust configuration setup. However, I am not sure yet on how to use this. Perhaps this is useful for this project? I am not so sure.

• Ooo from_envar() is a method to called your pre - made environmental variables.
• From this example app.config.from_envvar('FLASKR_SETTINGS', silent=true) means that this Flask web application will look into FLASKR_SETTING environment variable (in Linux, export FLASKR_SETTING=value_here) the silent=true means that this application will not complain if the setting value is not provided.

• Basically there is this function to connect the Flask web application with database.
• This tutorial used SQLite3 for database. So I am not sure if the method to connecting to database is different to non - lite SQL.
• Here are the codes to connecting to database.

def connect_db():
    rv = sqlite3.connect(app.config['DATABASE'])
    rv.row_factory = sqlite3.Row
    return rv

• There are little to no description on what this codes does.
• I think the sqlite.connect() is for connecting to the database.
• Then I suggest that its first argument is the database path which is located in app.config['DATABASE'].
• When assigning a variable into sqlite3.connect() I assume it returns the database object itself. Hence, the variable now has access to row_factory field.
• I am not sure on how the sqlite3.Row works.

• There is a method in Flask of where you can assign new command to be executed in terminal.

• So here is the basic setup to run the Flask web application.

export FLASK_APP=main_entry_of_your_flask_application.py
export FLASK_DEBUG=1
flask run

• The first line is to determine the entry point of this Flask web application.
• The second line is to set Flask application in debug mode. Means that the application will not required to be stopped and then run again to see the changes made.

• Use set instead of export when using Windows.
• Also never use debugging mode for a production system. Debugging mode will allow user to execute code in server.

• This was an example of the code working.
• There is nothing to display on '/' because the route is not yet set.

• Transaction encapsulation, I am not sure on why on the ideal case there will be only one request at the time that uses the database connection.
• What happen in the real time application if there are multiple request at the same time?

• Flask provides application context and the request context.
• In NodeJS' ExpressJS there are request and response handler. But in Flask there are the application context and the request context.
• I am not so sure if these notion from NodeJS's ExpressJS works the same with Flask.

• There is this flask.g object that can be used to store settings across sessions.

• There is a teardown_appcontext() decorator that will execute codes when the the application is closed in the client side. It says in this tutorial that teardown_appcontext() will be executed when a request finishes.
  • When everything went well (the error parameter will be None)
  • An exception happened.
• This is useful to disconnect the connection to the database.

• I am not sure why it is necessary to put all of these methods after connect_db() function.

• It is only says that this is logical to put methods for same module together.
• So, there would be no harm to put it alphabetically I guess.

• Flask is a database powered application.
• Hence, we need to create schema first for every database that we are going to make.

• Relational database is the SQL variants.
• Does this means that Flask is not intended to use with NoSQL databases like MongoDB?

• Basic command to create schema are as follows, sqlite3 /tmp/flaskr.db < schema.sql.
• However, the command needs to have sqlite3 CLI application to be installed.
• There is a Flask way to generate database from schema.
• It is also good to have in application method to build and initialize database for the application itself.

• I had this problem.
• I thought the problem lies on my Python codes.
• But the problem actually is in my schema file.
• It is supposed to be exists no exist.

• The sqlite3.Row makes the returned value looks like a Python's dictionary.

• When you can to refactor your project it is necessary to create new virtual environment.
• Delete the venv folder and initiate virtualenv venv again.
• Because otherwise the path will stay in the old project's directory.

• You need to use question marks when building SQL statement.
• Otherwise the application will be vulnerable to SQL injection.
• Example codes.

db.execute(
    'insert into entries (title, text) values (?, ?)',
    [request.form['title'], request.form['text']]
)