Flask App Not Showing New Database Records? Restarting Fixes It? Here's Why!
Problem: You've added new data to your database, but your Flask application refuses to show it until you restart the server. This is frustrating, as you'd expect changes to be reflected immediately.
Scenario: You've created a Flask app that displays a list of users from a database. When you add a new user through a form, the new user doesn't appear on the list until you restart the Flask app.
Original Code (Simplified Example):
from flask import Flask, render_template
from flask_sqlalchemy import SQLAlchemy
app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///users.db'
db = SQLAlchemy(app)
class User(db.Model):
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(80), unique=True, nullable=False)
@app.route('/')
def index():
users = User.query.all()
return render_template('index.html', users=users)
if __name__ == '__main__':
app.run(debug=True)
Understanding the Issue:
The problem lies in how Flask interacts with your database. Flask doesn't automatically "watch" your database for changes. It creates a connection to the database when it starts and holds onto that connection.
Solution:
The easiest solution is to enable autocommit in your database connection. By enabling autocommit, your database changes will be automatically committed to the database, making them immediately visible to your Flask application.
Here's how to do it:
-
Import the
sessionobject fromflask_sqlalchemy:from flask_sqlalchemy import SQLAlchemy, session -
Enable autocommit:
db.session.commit()Place this code snippet after adding a new user to your database, within the relevant route function.
Example:
@app.route('/add_user', methods=['POST'])
def add_user():
name = request.form.get('name')
new_user = User(name=name)
db.session.add(new_user)
db.session.commit() # Enable autocommit
return redirect('/')
Further Considerations:
- Debug Mode: When using Flask in debug mode (which is recommended for development), the server automatically reloads when it detects changes in your Python files. However, this doesn't affect database changes. Autocommit is still necessary for immediate updates.
- Production Environment: In production, you might want to consider alternative solutions like database triggers or background tasks that update your Flask application when changes happen in the database.
- Database Type: The specific way to enable autocommit might differ slightly depending on your database system (e.g., MySQL, PostgreSQL).
By enabling autocommit, you ensure that your Flask application can immediately see changes in your database, eliminating the need for server restarts.
