using sqlalchemy cannot commit to database

Question

I'm making a video page can track played time and comment time, every time I reload the page, using {{ movie.play_num }} to display the played time, it's always working but it won't change the database, So I don't know how can it be right? Seems like the session.commit() doesn't work. Besides, if I put some words in the comment field and submit, a waiting for response... shows up and looks like the server keep waiting until timeout.

Here's my code:

def play(id=None):
    movie = Movie.query.join(Tag).filter(
        Tag.id == Movie.tag_id,
        Movie.id == int(id)
    ).first_or_404()
    form = CommentForm()
    if "user" in session and form.validate_on_submit():
        data = form.data
        comment = Comment(
            content=data["content"],
            movie_id=movie.id,
            user_id=session["user_id"]
        )
        db.session.add(comment)
        db.session.commit() # problem here
        movie.comment_num = movie.comment_num + 1
        flash("Success", "ok")
        return redirect(url_for("home.play", id=movie.id))
    movie.play_num = movie.play_num + 1
    try:
        db.session.commit() # and problem here
    except:
        db.session.rollback()
    return render_template("home/play.html", movie=movie, form=form)

see the play_num has changed to 1 from 0, this is the first time I reload the page, but at the second time, the page can't be open, and the console can't collect any data.An error occurred:

This Session's transaction has been rolled back due to a previous exception during flush. To begin a new transaction with this Session, first issue Session.rollback(). Original exception was: (raised as a result of Query-invoked autoflush; consider using a session.no_autoflush block if this flush is occurring prematurely) (pymysql.err.InternalError)

How to fix this

Is your database connection setup correctly? What's the result if inserting a comment in python console? — cgcgbcbc
– cgcgbcbc, Commented Mar 14, 2019 at 2:15
How about putting a breakpoint after the commit to verify if it really the commit problem — cgcgbcbc
– cgcgbcbc, Commented Mar 14, 2019 at 3:30
Can you really update data like that when you perform a join in your query ? — Lycos IUT
– Lycos IUT, Commented Mar 14, 2019 at 10:07
It is not possible to answer this properly without seeing the error tracebacks — snakecharmerb
– snakecharmerb, Commented May 16 at 17:32

Alex · Accepted Answer · 2019-03-14 03:54:53Z

1

you try catch the exception msg:

from sqlalchemy.exc import SQLAlchemyError
try:
    db.session.commit()
except SQLAlchemyError as e:
    print(str(e))
    db.session.rollback()

check what the error msg first

answered Mar 14, 2019 at 3:54

Alex

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1 Comment

Klawens Over a year ago

It didn't go through the except way, it did choose to commit but the data never changed in database

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