Package: django-shouty-orm
Author:Keryn KnightVersion:0.1.1RationaleI want to useMyModel.objects.only()and.defer()because that’s thecorrectthing to do, even if it’s not the default thing Django does. But
using.only()and.defer()in Django is an absolute footgun because any
attempt to subsequently access the missing fields will …do another querySimilarly, I don’t want Django to silently allow me to do N+1 queries for related
managers/querysets. But it does, so there’s another footgun.This module then, is my terrible attempt to fix the footguns automatically, by
forcing them to raise exceptions where possible, rather than do the query. This
flies in the face of some other proposed solutions over the years on the mailing list,
such as automatically doingprefetch_relatedorselect_related.I think/hope that the package pairs well withdjango-shouty-templatesto try
and surface some of the small pains I’ve had over the years.What it doesAll of the following examples should raise an exception because they pose a probable
additional +1 (or more) queries.Accessing fields intentionally not selected:>>> u = User.objects.only('pk').get(pk=1)
>>> u.username
MissingLocalField("Access to username [...]")
>>> u = User.objects.defer('username').get(pk=1)
>>> u.email
>>> u.username
MissingLocalField("Access to username [...]")Access to relationships that have not been selected:>>> le = LogEntry.objects.get(pk=1)
>>> le.action_flag
>>> le.user.pk
MissingRelationField("Access to user [...]")Access to reverse relationships that have not been selected:>>> u = User.objects.only('pk').get(pk=1)
>>> u.logentry_set.all()
MissingReverseRelationField("Access to logentry_set [...]")Pretty much all relationship access (normal or reverse,OneToOneorForeignKeyorManyToMany) should be blocked unlessselect_relatedorprefetch_relatedwere used to include them.SetupAddshoutyormorshoutyorm.Shoutto yoursettings.INSTALLED_APPSI’d certainly suggest that you should only enable it whenDEBUGisTrueor
during your test suite.DependenciesDjango 2.2+ (obviously)wrapt1.11+ (for proxying managers/querysets transparently)Optional configurationsettings.SHOUTY_LOCAL_FIELDSmay beTrue|FalseAccessing fields which have been deferred via.only()and.defer()at the
QuerySet level will error loudly.settings.SHOUTY_RELATION_FIELDSmay beTrue|FalseAccessing OneToOnes which have not been.select_related()at the QuerySet
level will error loudly.
Accessing local foreignkeys which have not beenprefetch_related()orselect_related()at the queryset level will error loudly.settings.SHOUTY_RELATION_REVERSE_FIELDSmay beTrue|FalseAccessing foreignkeys from the “other” side (that is, via the reverse relation
manager) which have not been.prefetch_related()at the QuerySet level will error loudly.TestsJust runpython3-mshoutyormand hope for the best. I usually do.AlternativesA similar similar approach is taken bydjango-sealbut without the
onus/burden of subclassing from specific models. I’ve not looked at the
implementation details of how seal works, but I expect I could’ve saved myself
quite a lot of headache by seeing what steps it takes in what circumstances,
rather than constantly hitting breakpoints and inspecting state.A novel idea is presented indjango-eraserheadof specifically calling out
when you might be able to usedefer()andonly()to reduce your selections,
but introducing those optimisations still poses a danger of regression without a
test suite and this module.Having started writing this list of alternatives, I am reminded ofnplusoneand it turns out that has Django supportanda setting for raising exceptions…
So all of this patch may be moot, because I expect that covers a lot more? Again
I’ve not looked at their implementation but I’m sure it’s miles better than this
abomination.The licenseIt’sFreeBSD. There’s should be aLICENSEfile in the root of the repository, and in any archives.Copyright (c) 2020, Keryn Knight
All rights reserved.Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS “AS IS” AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.Change history for django-shouty-orm0.1.1Initial release