results of sqlite query not displayed in flask web app - python-3.x

Question

I'm attempting to learn flask, so decided to follow this tutorial:
https://www.blog.pythonlibrary.org/2017/12/14/flask-101-adding-editing-and-displaying-data/
I just updated my main function with the below:
#app.route('/results')
def search_results(search):
results = []
search_string = search.data['search']
if search.data['search'] == '':
qry = db_session.query(Album)
results = qry.all()
if not results:
flash('No results found!')
return redirect('/')
else:
# display results
table = Results(results)
table.border = True
return render_template('results.html', table=table)
but when I add an album to the DB and try to query it back using search option it says no results. The DB file was created correctly and I have exactly the same code as in the tutorial up to this point.
The only change I made was adding from tables import Results. Full main.py below. Can you please give me some guidance about where to look for the culprit? Like I said, just learning, so any suggestions re resources in a friendly laid out way would be much appreciated (beginner programmer).
from app import app
from db_setup import init_db, db_session
from forms import MusicSearchForm, AlbumForm
from flask import flash, render_template, request, redirect
from models import Album, Artist
from tables import Results
init_db()
def save_changes(album, form, new=False):
"""
Save the changes to the database
"""
# Get data from form and assign it to the correct attributes
# of the SQLAlchemy table object
artist = Artist()
artist.name = form.artist.data
album.artist = artist
album.title = form.title.data
album.release_date = form.release_date.data
album.publisher = form.publisher.data
album.media_type = form.media_type.data
if new:
# Add the new album to the database
db_session.add(album)
# commit the data to the database
db_session.commit()
#app.route('/', methods=['GET', 'POST'])
def index():
search = MusicSearchForm(request.form)
if request.method == 'POST':
return search_results(search)
return render_template('index.html', form=search)
#app.route('/results')
def search_results(search):
results = []
search_string = search.data['search']
if search.data['search'] == '':
qry = db_session.query(Album)
results = qry.all()
if not results:
flash('No results found!')
return redirect('/')
else:
# display results
table = Results(results)
table.border = True
return render_template('results.html', table=table)
#app.route('/new_album', methods=['GET', 'POST'])
def new_album():
"""
Add a new album
"""
form = AlbumForm(request.form)
if request.method == 'POST' and form.validate():
# save the album
album = Album()
save_changes(album, form, new=True)
flash('Album created successfully!')
return redirect('/')
return render_template('new_album.html', form=form)
if __name__ == '__main__':
app.run()

Answer 1

No doubt you have already peppered your source code with print() statements and found nothing illuminating. Cached rows in the DB model might be the aspect that is hard to understand, here, and logging sqlite calls would shed light on that.
Use this:
import logging
logging.getLogger('sqlalchemy.engine').setLevel(logging.INFO)
It's noisy, but it will show when rows hit the backend DB and when they are retrieved.
Get in the habit of repeatedly issuing debug queries like this, so you know for sure what has been persisted:
$ echo 'select * from album;' | sqlite3 music.db
For repeatable testing, it can be convenient to copy the database file to a backup location, and then cp that frozen snapshot on top of the active file before each test run. It's important that the running flask app be restarted after such copying. Setting FLASK_DEBUG=1 can help with that.
Also, jeverling suggests using SQLAlchemyDebugPanel.