Flask Blog Application

Introduction

In this lab, we'll walk through creating a blog application using Flask, a popular web framework in Python. This application will list all blog posts, allow logged-in users to create posts, and let authors edit or delete their own posts.

Note: You need to create the code file yourself and run it in the environment. You can preview the Flask service status on Web 5000.

Skills Graph

Define Blueprint

Firstly, we'll define a blueprint for our blog. A blueprint is a way to organize a group of related views and other code.

## flaskr/blog.py

from flask import Blueprint, flash, g, redirect, render_template, request, url_for
from werkzeug.exceptions import abort

from flaskr.auth import login_required
from flaskr.db import get_db

## The Blueprint is named 'blog'. It's defined in the same file.
## The blueprint needs to know where it's defined, so __name__ is passed as the second argument.
bp = Blueprint('blog', __name__)

Register Blueprint

Next, we'll register the blueprint with our application.

## flaskr/__init__.py

def create_app():
    app = ...
    ## existing code omitted

    ## import and register the blueprint from the factory using app.register_blueprint()
    from . import blog
    app.register_blueprint(blog.bp)
    app.add_url_rule('/', endpoint='index')

    return app

Create Blog Index

Now, let's create an index view to display all blog posts. We'll use a SQL JOIN to include author information from the user table in our results.

## flaskr/blog.py

@bp.route('/')
def index():
    db = get_db()
    posts = db.execute(
        'SELECT p.id, title, body, created, author_id, username'
        ' FROM post p JOIN user u ON p.author_id = u.id'
        ' ORDER BY created DESC'
    ).fetchall()
    return render_template('blog/index.html', posts=posts)

Post Creation

Next, we'll create a view that allows logged-in users to create new blog posts.

## flaskr/blog.py

@bp.route('/create', methods=('GET', 'POST'))
@login_required
def create():
    if request.method == 'POST':
        title = request.form['title']
        body = request.form['body']
        error = None

        if not title:
            error = 'Title is required.'

        if error is not None:
            flash(error)
        else:
            db = get_db()
            db.execute(
                'INSERT INTO post (title, body, author_id)'
                ' VALUES (?, ?, ?)',
                (title, body, g.user['id'])
            )
            db.commit()
            return redirect(url_for('blog.index'))

    return render_template('blog/create.html')

Post Update

We'll add the ability for authors to update their own posts. To avoid duplicating code, we'll create a helper function to get a post and check if the current user is the author.

## flaskr/blog.py

@bp.route('/<int:id>/update', methods=('GET', 'POST'))
@login_required
def update(id):
    post = get_post(id)

    if request.method == 'POST':
        title = request.form['title']
        body = request.form['body']
        error = None

        if not title:
            error = 'Title is required.'

        if error is not None:
            flash(error)
        else:
            db = get_db()
            db.execute(
                'UPDATE post SET title = ?, body = ?'
                ' WHERE id = ?',
                (title, body, id)
            )
            db.commit()
            return redirect(url_for('blog.index'))

    return render_template('blog/update.html', post=post)

Post Deletion

Lastly, we'll add the ability for authors to delete their own posts.

## flaskr/blog.py

@bp.route('/<int:id>/delete', methods=('POST',))
@login_required
def delete(id):
    get_post(id)
    db = get_db()
    db.execute('DELETE FROM post WHERE id = ?', (id,))
    db.commit()
    return redirect(url_for('blog.index'))

Summary

Congratulations, you've created a simple blog application using Flask! This application supports user authentication, and allows users to create, edit, and delete their own blog posts.