405 Method Not Allowed When Redirecting in Flask within POST route

Question

I'm hoping to shed some light on why I am getting a 405 Method Not Allowed error.

Expected Outcome - User should be redirected to manage.html template when they attempt to add a review to a game they have already added a review to.

Actual Outcome - 405 Error (Method Not Allowed) Displayed.

Manage Route:

@app.route('/manage')
def manage():
    """Renders manage.html template."""
    return render_template('manage.html')

Submit Review Route:

@app.route('/submit_review/<game_id>', methods=['POST'])
def submit_review(game_id):
    """
    Add users review to database.
    """
    user = User.query.filter_by(username=session['username']).first()
    existing_review = Review.query.filter_by(user_id=user.id,
                                             game_id=game.id).first()

    if existing_review:
        flash('You have already created a review for this game')
        return redirect(url_for('manage'))
...

What I Have Tried: I've done some reading of the flask documentation, specifically around flask.redirect (docs), and searched for other examples, but I have been unable to find something that resolves my issue.

I have a hunch that when the user submits the form, and they have already have a review for that particular game, the POST request is also being redirected to the "manage" route.

I checked the network tab in dev tools and it is a GET request, which is correct for that URL.

I guess what I'm trying to say is... I have no idea why this is happening, so don't know how to search for a resolution.

Screenshot of Network -> Headers tab in dev tools:

Server Console:

[10/May/2022 18:43:49] "POST /submit_review/11198 HTTP/1.1" 302 -

[10/May/2022 18:43:49] "review-rating=0&review-heading=&liked-text=&disliked-text=&review-hours=1&game-name=Rocket+League&igdb-id=&igdb-summary=&igdb-cover-url=&action=GET /manage HTTP/1.1" 405 -

Answer 1

Firstly, Thank you @Henry for the inspiration to finding a solution.

Secondly, I have learnt that including the entire function in the original question, and not just what I feel may be relevant, may have resolved this much sooner.

The Answer.

@Henry mentioned that as per the docs for url_for() - "Variable arguments that are unknown to the target endpoint are appended to the generated URL as query arguments."

This is my take on the situation.

The submit_review() function was returning before the form data was being used, meaning that the form data was unknown to the target endpoint.

Function Before Fix:

@app.route('/submit_review/<game_id>', methods=['POST'])
def submit_review(game_id):
    """
    Adds users review to database.
    """

    existing_game = Game.query.filter_by(igdb_id=game_id).first()

    if not existing_game:
        igdb_game_data = get_game_data_by_id(game_id)[0]
        igdb_game_artwork = get_game_artwork(game_id)
        igdb_game_cover = get_game_cover_art(game_id)

        game = Game(
            name=igdb_game_data['name'],
            artwork=json.dumps(igdb_game_artwork),
            summary=igdb_game_data['summary'],
            igdb_id=igdb_game_data['id'],
            cover_art=igdb_game_cover
        )

        db.session.add(game)
        db.session.commit()

    user = User.query.filter_by(username=session['username']).first()
    game = Game.query.filter_by(igdb_id=game_id).first()

    existing_review = Review.query.filter_by(user_id=user.id,
                                             game_id=game.id).first()

    if existing_review:
        print(request)
        flash('You have already created a review for this game')
        return redirect(url_for('manage'))

    review = Review(
        user_id=user.id,
        game_id=game.id,
        rating=float(request.form.get('review-rating')),
        heading=request.form.get('review-heading'),
        liked_text=request.form.get('liked-text'),
        disliked_text=request.form.get('disliked-text'),
        hours=int(request.form.get('review-hours')),
    )

    db.session.add(review)
    db.session.commit()

    flash('Review added successfully')
    return redirect(url_for('home'))

By moving where the form data is used, I got the expected results, functionality is correct, as the review is not added to the database if a review for that game, by the same user is present.

Function After Fix:

@app.route('/submit_review/<game_id>', methods=['POST'])
def submit_review(game_id):
    """
    Adds users review to database.
    """

    existing_game = Game.query.filter_by(igdb_id=game_id).first()

    if not existing_game:
        igdb_game_data = get_game_data_by_id(game_id)[0]
        igdb_game_artwork = get_game_artwork(game_id)
        igdb_game_cover = get_game_cover_art(game_id)

        game = Game(
            name=igdb_game_data['name'],
            artwork=json.dumps(igdb_game_artwork),
            summary=igdb_game_data['summary'],
            igdb_id=igdb_game_data['id'],
            cover_art=igdb_game_cover
        )

        db.session.add(game)
        db.session.commit()

    user = User.query.filter_by(username=session['username']).first()
    game = Game.query.filter_by(igdb_id=game_id).first()

    existing_review = Review.query.filter_by(user_id=user.id,
                                             game_id=game.id).first()

    review = Review(
        user_id=user.id,
        game_id=game.id,
        rating=float(request.form.get('review-rating')),
        heading=request.form.get('review-heading'),
        liked_text=request.form.get('liked-text'),
        disliked_text=request.form.get('disliked-text'),
        hours=int(request.form.get('review-hours')),
    )

    if existing_review:
        print(request)
        flash('You have already created a review for this game')
        return redirect(url_for('manage'))

    db.session.add(review)
    db.session.commit()

    flash('Review added successfully')
    return redirect(url_for('home'))