[Flask] g/session/request

[Corey Boyle]

I could be wrong about this, but...

The default session storage is done with cookies, so if you store the
data in the session, all that data will get shipped back and forth
with each request made by the client. Also, cookies have a storage
limit that may be an issue.

The "g" proxy object is tied to the request context, so anything
stored on it will be garbage collected when the request is fulfilled.

Option 1 - Create a new function outside your view function used
solely for building your data. Either write some custom caching code
inside that function, or use something like Flask-Caching. Then call
that function inside your view function.

Option 2 - Build the table in HTML as you are now, and allow the
sorting to be done on the client side using JS. DataTables
(https://datatables.net) is AMAZING and actually pretty easy to figure
out.

Option 3 - Option 1 + Option 2... Doing the sorting on the client side
would be much more efficient, and caching the data on the server side
would be advisable is you are expecting to handle many requests
simultaneously.

On Fri, Jun 2, 2017 at 9:48 AM, Craig Amundsen <amundsen.craig at gene.com> wrote:
> Hi -
>
> I'm trying to implement a sortable table using Flask-Table. My dummy test
> works great. But querying my database and building the list of  dictionaries
> that the Table instance uses takes a certain amount of time. I'd like to
> keep that list of dictionaries around so when the User sorts on a different
> column I don't have to build it again.
>
> Currently I have one page where the User indicates which information they
> want in the table. When they click on the submit button I query the
> database, construct the dictionary, store the dictionary in the session, and
> then call view that shows the table. That method grabs the dictionary out of
> the session and constructs the table which is then sent to the html
> template. This all works great.
>
> Clicking on a column heading ends up calling the view that shows the table
> again. This time, though, the session doesn't have the dictionary and so an
> error gets thrown.
>
> I tried messing about with g, but I can't get that to work either. Does
> anyone have any hints on how I can save list so it's still available when I
> sort the table?
>
> Here's some snippets to show what I'm doing:
>
> @main.route('/select-data', methods = ['GET', 'POST'])
> @login_required
> @view_data_required
> def select_data():
>     form = SelectDataForm()
>     if form.validate_on_submit():
>         colsToShow = { 'showName' : True,
>                        'showX'    : form.showX.data,
>                        'showY'    : form.showY.data,
>                        'showZ'    : form.showZ.data }
>         session.dataFlags = colsToShow
>
>         # Build the list that Table wants
>
>         session.theList = theList
>         return show_data()
>     return render_template(select_data.html", form = form)
>
> @main.route('/show-data')
> @login_required
> @view_data_required
> def show_data():
>     colsToShow =  session.dataFlags
>
>     TableClass = create_table()
>     for key, attr, header in [('showName', 'name', "Name"), ('showX', 'x',
> "X"),
>                               ("showY", "y", "Y"), ("showZ", "z", "Z")]:
>         if colsToShow[key]:
>             TableClass.add_column(attr, Col(header))
>
>     TableClass.allow_sort = True
>     TableClass.sort_url = sort_url
>     TableClass.classes = ["table", "table-hover", "followers"]
>
>     sort = request.args.get('sort', 'name')
>     direction = request.args.get('direction', 'asc')
>     reverse = (request.args.get('direction', 'asc') == 'desc')
>
>     theList = session.theList
>     theList = sorted(theList, key = lambda x: x[sort], reverse = reverse)
>     table = TableClass(things, sort_by = sort, sort_reverse = reverse)
>
>     return render_template("dump_data.html", table = table, sort = sort,
> direction = direction)
>
> def sort_url(self, col_key, reverse=False):
>     if reverse: direction = 'desc'
>     else: direction = 'asc'
>     return url_for('.show_data', sort=col_key, direction=direction)
>
>
> I've tried re-assigning session.theList and session.colsToShow at the bottom
> of show_data, but that doesn't work. I've tried messing around with with g
> instead of session, but I don't seem to grasp its use any better.
>
> If anyone has any hints on making the session/g/request know about the two
> things I need to store there the second time I call show_data (by clicking
> on a column header), I'd be most appreciative.
>
> Thanks,
> - Craig
>
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