I was learning to work with Flask, SQLAlchemy and WTForms so I created this simple todo app as reference to my future self and starting point for new apps. This example can be easily expanded to add new functions.

Setting up initial install

Let's start by cloning this repo:

$ git clone https://github.com/KingOfSpades/flaskTodoAppDemo.git
$ cd flaskTodoAppDemo

As always you should start with an empty venv, activate it and install the required dependancys:

$ python3 -m venv .venv
$ source .venv/bin/activate
$ pip install -r requirements.txt

Now you can fill initalize the database with some dummy data by using make:

$ make database

This will create the inital database we need with some sample todo's. Have a look in flaskr/initDB.py if you want to see what's going on.

Now start the app with make or run it manually:

$ make run

This will start the app on: http://127.0.0.1:5000. You should now see this beautifull todo app:

Explaining the app

This is easy app tha relies on one (1) database model, a FlaskForm and four (4) routes to handle requests:

• / route handels returinging the main page and index
• /add route is used to add new todo's
• /update route is used to update a todo based on the provided id. In our case it togles the done status of a todo
• /delete route deletes a todo based on the provide id

Diagram overview

flowchart LR
    browser --> / --> |return| render(index)
    browser --> /add --> add --> |redirect| /
    browser --> /update/int:id --> update --> |redirect| /
    browser --> /delete/int:id --> delete --> |redirect| /
    render ---> |shows application| browser
    db --> |provides data| render

    
   add -.-> |add| db[(Database)]
   update -.-> |update| db[(Database)]
   delete -.-> |delete| db[(Database)]

Loading

Forms

The app uses a single form linked to a class to generate the add form:

# flaskr/app.py
...
# Todo form for adding items
class TodoForm(FlaskForm):
  todo = StringField("Todo")
  submit = SubmitField("Add")
...

This form is then renderd in the index.html template:

# flaskr/templates/index.html
...
<form method="POST" action="/add" class="input-group">
  <div class="form-outline flex-fill">
  {{ template_form.hidden_tag() }}
    {{ template_form.todo(
      class_='form-control',
      placeholder='Add a new todo ...',
      required='required'
      ) 
    }}
    {{ template_form.submit(class_='btn btn-primary btn-sm  btn-block') }}
  </div>
</form>
...

Database

The database consists of a simple class to hold an id, todo_text and the state of the Todo (completed, True or False):

# flaskr/app.py
# Todo class/model for holding todo's
class Todo(db.Model):
  id = db.Column(db.Integer, primary_key = True)
  todo_text = db.Column(db.String(256), index = True)
  completed = db.Column(db.Boolean, unique=False, default=False)

Updating todo's

This is simply done by rendering the target URL + todo ID, for example:

/delete/{{ todo.id }}