Update random row in DB using Flask-Sqlalchemy - sqlite

Question

I've been trying to update a randomly selected row in my Sqlite database using Flask and the Flask-Sqlalchemy. I have just a few rows in the database with columns called "word", "yes", and "no", where word is a string and yes and no are integers. There are two buttons on the "vote" view, yes and no. When a button is pressed, the appropriate code executes, should increment the yes or no column, and the view is updated with a new random word from the Word table.
#app.route("/vote", methods=["GET", "POST"])
def vote():
#Get random row from database
query = db.session.query(Word)
rowCount = int(query.count())
row = query.offset(int(rowCount*random.random())).first()
#POST
# If "yes" button is pressed, increment yes column in database
if request.method == "POST":
if request.form.get("yes"):
row.yes += 1
db.session.commit()
return render_template("vote.html", row=row)
# otherwise increment no column
elif request.form.get("no"):
row.no += 1
db.session.commit()
return redirect(url_for("vote"))
#GET
# on get request, render vote.html
return render_template("vote.html", row=row)
This code is working, but the yes and no columns are only updated when the view comes back around to the random word the next time. If I close the browser right after clicking a button, the database is not incremented. I think this has something to do with db.session.commit(), or something about the session. It seems like:
row.yes += 1
is saved in the session object, but only committed when that database row is queried the next time. This code DID work when I replaced the query at the top of the method with:
row = Word.query.get(4)
which returns the row with id of 4. With this query, the yes or no column are updated immediately.
Any thoughts?
Thanks

Answer 1

Thanks all. I figured out the problem. The database incrementing was actually working fine, but I wasn't incrementing the correct rows. The problem was that I generated a random row from the database on each call of the vote() method, which meant that I got a random value for the GET request, and a different random value for the POST request, and ended up incrementing that different random value in the POST request.
I separated the logic out into two methods for the "/vote" route, getWord() and vote(), and created a randRow() method for the row generation. I needed to store the random row that gets generated when getWord() is called, so I used session variables so I could access the random row from the vote() method. It's a bit verbose, but seems to work.
Anyone have a better idea about how to achieve this?
#app.route('/vote', methods=["GET"])
def getWord():
wordObj = randRow()
session['word'] = wordObj.word
session['yesVotes'] = wordObj.yes
session['noVotes'] = wordObj.no
return render_template("vote.html", word=session['word'], yesVotes=session['yesVotes'], noVotes=session['noVotes'])
#app.route('/vote', methods=["POST"])
def vote():
# store session 'word' in word variable
# look up word in database and store object in wordObj
word = session['word']
wordObj = Word.query.filter_by(word=word).first()
# check button press on vote view, increment yes or no column
# depending on which button was pressed
if request.form.get("yes"):
wordObj.yes = wordObj.yes + 1
elif request.form.get("no"):
wordObj.no = wordObj.no + 1
db.session.commit()
return redirect(url_for("getWord"))
###### HELPERS ######
# returns a random row from the database
def randRow():
rowId = Word.query.order_by(func.random()).first().id
row = Word.query.get(rowId)
return row

Answer 2

I think you need to add the update into the session before the commit, using code like this:
[...]
row.yes += 1
db.session.add(row)
db.session.commit()
[...]
That's the pattern that I use for a basic update in Flask-SQLAlchemy.