I'm mixing my versions, sorry to those following along. 1.9 has just
reached alpha. Lookups as Expressions should be doable for 1.10 which
master is currently tracking.
Cheers
On Wednesday, 30 September 2015 15:31:24 UTC+10, Josh Smeaton wrote:
>
> The alpha for 1.10 has already been cut, and I'm not sure that the kinds
> of changes needed here are appropriate to add now that the alpha is out.
> One could *maybe* make the argument that changing Lookup to an Expression
> now rather than later is the right move considering Transforms just
> underwent the same change for 1.10. Personally though, I don't think I have
> the time right now to do this change. I would support you if you were able,
> but we'd still be at the mercy of the technical board (I assume) for
> getting this change in for 1.10.
>
> Do you think Lookup as Expressions requires the subquery/exclude fix you
> mention above? I would think not -- not until we were ready to document and
> support .filter(Lookup(F(), Value()). If it wasn't a requirement, it'd make
> the Lookup->Expression work much easier. It wouldn't even need to be
> documented (other than the release notes), as it'd just be an
> implementation change.
>
> Cheers,
>
> On Wednesday, 30 September 2015 14:33:14 UTC+10, Anssi Kääriäinen wrote:
>>
>> On the core ORM side we need to make
>> .exclude(LessThan(F('friends__age'), 30)) do a subquery. This way
>> .exclude(friends__age__lt=30) does the same thing as the expression
>> version. This isn't that easy to do. If we just use
>> resolve_expression, then the friends relation will generate a join,
>> and then as second step do a negated filter on the joined value.
>> Instead we want to detect that the LessThan expression needs to be
>> pushed in to a subquery.
>>
>> So, we need to solve:
>>
>> A) A way to ask an expression if it is referencing a multijoin
>> (possible approach is to just have a method
>> "refs_multi_valued_relation(query)")
>> B) When the ORM sees an expression that is reffing a multijoin in an
>> exclude filter, then we need to push the expression in to a subquery.
>>
>> A) requires some new work. This shouldn't be that hard to implement,
>> we just recursively ask subexpressions if they reference a multijoin.
>>
>> Something like https://github.com/django/django/pull/4385 will make B)
>> much easier to implement.
>>
>> I've been working on making Q-objects responsible for resolving
>> themselves. See https://github.com/django/django/pull/4801. This
>> should solve 3).
>>
>> We don't seem to be missing any major parts. I (or some volunteer)
>> just need to finish the PRs, and then we should be really close to
>> full support for expressions in filter.
>>
>> Josh: do you think we could get Lookup as expressions in to 1.10
>> instead of 1.11?
>>
>> - Anssi
>>
>> On Wed, Sep 30, 2015 at 3:46 AM, Josh Smeaton <josh.s...@gmail.com>
>> wrote:
>> > 1. Lookups should become Expressions, just as Transforms have become
>> > Expressions. This will let us process Lookup arguments as Expressions
>> all
>> > the way the way through. I think this should be a major goal for
>> version
>> > 1.11.
>> >
>> > 2. Chaining transforms is now possible since they are just Func
>> expressions.
>> > Func(Func(Func('field_name'))) is no issue.
>> >
>> > 3. Sounds like an OK idea, but I haven't looked into the details enough
>> to
>> > really comment. I do think we should create the correct form as early
>> as
>> > possible (parsing into a chain of Lookup/Transform expressions) so we
>> don't
>> > have to do parsing in multiple places. The entry points to .filter()
>> and
>> > .exclude(), or their direct counterparts in sql.query sound ideal.
>> Anssi has
>> > mentioned elsewhere that WhereNode's should only contain fully resolved
>> > expressions, so resolving will need to be done directly after parsing
>> (or
>> > during).
>> >
>> > Part 1 above can be started now if you have the time or interest. We
>> can
>> > nail down the particulars of part 3 while we're solving part 1. Part 1
>> may
>> > drive some of part 3.
>> >
>> > Cheers
>> >
>> >
>> > On Wednesday, 30 September 2015 04:49:54 UTC+10, Alexey Zankevich
>> wrote:
>> >>
>> >> Here is a list of issues to solve to support explicit transforms and
>> >> lookups by filter (and exclude) methods.
>> >>
>> >> 1. Make Lookup.__init__ signature to support initialization with F
>> objects
>> >> or string path (e.g. GreaterThan(F('user__id'), 10) or
>> >> GreaterThan('user__id', 10)), not sure it's possible to use
>> simultaneously
>> >> with the current approach with lhs, rhs initialization (even with
>> moving it
>> >> to a separate class method, e.g Lookup.build(lhs, rhs)), so I assume
>> >> creating so-called util classes which will delegate SQL-related
>> >> functionality to existing Lookup classes.
>> >>
>> >> 2. Chain transforms by passing them as argument:
>> >>
>> >> Lower(Unaccent(F('user__name)))
>> >>
>> >> 3. Decide if Q objects shall support explicit lookups/transforms as
>> >> argument as well - it's a kind of logical step, as without Q objects
>> it will
>> >> not be possible to perform complicated conditions (AND, OR, NOT).
>> >> In that case lookup/transform parsing should be moved from QuerySet
>> object
>> >> to Q object - filter will take already parsed lookup tree.
>> >> Example:
>> >>
>> >> Q(user__name__lower__unaccent__icontains='Bob') will internally parse
>> it
>> >> and build next structure:
>> >>
>> >> Q(Icontains(Lower(Unaccent(F('user__name')))), 'Bob')
>> >>
>> >>
>> >> On Sunday, August 16, 2015 at 4:18:26 PM UTC+3, Alexey Zankevich
>> wrote:
>> >>>
>> >>> Hi all,
>> >>>
>> >>> This topic is related to the current ORM query syntax with
>> underscores.
>> >>> There are lots of arguing related to it, anyway it has pros and cons.
>> >>>
>> >>> Let's take a concrete example of querying a model:
>> >>>
>> >>> >>>
>> >>> >>>
>> GameSession.objects.filter(user__profile__last_login_date__gte=yesterday)
>> >>>
>> >>>
>> >>> Pros:
>> >>>
>> >>> 1. The syntax is easy to understand
>> >>> 2. Can be extended with custom transforms and lookups
>> >>>
>> >>> However, there are several cons:
>> >>>
>> >>> 1. Long strings is hard to read, especially if we have fields with
>> >>> underscores.
>> >>> It's really easy to make a mistake by missing one:
>> >>>
>> >>> >>>
>> >>> >>>
>> GameSession.objects.filter(user_profile__last_login_date__gte=yesterday)
>> >>>
>> >>> Not easy to catch missing underscore between user and profile, is it?
>> >>> Even
>> >>> though, it's not easy to say whether it should be "user_profile"
>> >>> attribute or
>> >>> user.profile foreign key.
>> >>>
>> >>> 2. Query strings can't be reused, thus the approach violates DRY
>> >>> principle.
>> >>> For example, we need to order results by last_login_date:
>> >>>
>> >>> >>>
>> >>> >>>
>> GameSession.objects.filter(user__profile__last_login_date__gte=yesterday) \
>> >>> .order_by('user__profile__last_login_date')
>> >>>
>> >>> We can't keep user__profile_login_date as a variable as in the first
>> part
>> >>> of the
>> >>> expression we use a keyword argument, meanwhile in the second part -
>> just
>> >>> a
>> >>> string. And thus we just have to type query path twice.
>> >>>
>> >>> 3. Lookup names not natural to Python language and require to be
>> >>> remembered or
>> >>> looked up in documentation. For example, "__gte" or "__lte" lookups
>> tend
>> >>> to be
>> >>> confused with "ge" and "le" due to similarity to methods "__ge__" and
>> >>> "__le__".
>> >>>
>> >>> 4. Lookup keywords limited to a single argument only, very
>> inconvenient
>> >>> when
>> >>> necessary to filter objects by range.
>> >>>
>> >>> I was thinking a lot trying to solve those issues, keeping in mind
>> Django
>> >>> approaches. Finally I came up with solution to extend Q objects with
>> dot
>> >>> expression syntax:
>> >>>
>> >>> >>> GameSession.objecs.filter(Q.user.profile.last_login_date >=
>> >>> >>> yesterday)
>> >>>
>> >>> Q is a factory instance for old-style Q objects. Accessing attribute
>> by
>> >>> dot
>> >>> returns a child factory, calling factory will instantiate old-style Q
>> >>> object.
>> >>>
>> >>> >>> Q
>> >>> <QFactory object at 0x7f407298ee10>
>> >>>
>> >>> >>> Q.user.profile
>> >>> <QFactory object at 0x7f40765da310>
>> >>>
>> >>> >>> Q(user__name='Bob')
>> >>> <Q: (AND: ('user__name', 'Bob'))>
>> >>>
>> >>> It overrides operators, so comparing factory with value returns a
>> related
>> >>> Q
>> >>> object:
>> >>>
>> >>> >>> Q.user.name == 'Bob'
>> >>> <Q: (AND: ('user__name', 'Bob'))>
>> >>>
>> >>> Factory has several helper functions for lookups which aren't related
>> to
>> >>> any
>> >>> Python operators directly:
>> >>>
>> >>> >>> Q.user.name.icontains('Bob')
>> >>> <Q: (AND: ('user__name__icontains', 'Bob'))>
>> >>>
>> >>> And helper to get query path as string, which requred by order_by or
>> >>> select_related queryset methods:
>> >>>
>> >>> >>> Q.user.profile.last_login_date.get_path()
>> >>> 'user__profile__last_login_date'
>> >>>
>> >>> You can check implementation and more examples here
>> >>> https://github.com/Nepherhotep/django-orm-sugar
>> >>>
>> >>> How it solves issues:
>> >>>
>> >>> #1. Dots hard to confuse with underscores
>> >>> #2. Query paths can be reused:
>> >>>
>> >>> >>> factory = Q.user.profile.last_login_date
>> >>> >>> query = GameSession.objects.filter(factory >= yesterday)
>> >>> >>> query = query.order_by(factory.get_path())
>> >>>
>> >>> #3. Not neccessary to remember most of lookup names and use
>> comparison
>> >>> operators
>> >>> instead.
>> >>> #4. Possible to use multiple keyword arguments:
>> >>>
>> >>> >>> Q.user.profile.last_login_date.in_range(from_date, to_date)
>> >>> <Q: (AND: ('user__profile__last_login_date__lte', from_date),
>> >>> ('user__profile__last_login_date__gte', to_date))>
>> >>>
>> >>>
>> >>> This approach looked the best for me due to several reasons:
>> >>>
>> >>> 1. It's explicit - it doesn't do anything but generating appropriate
>> Q
>> >>> object.
>> >>> The result of comparison can be saved as Q object variable.
>> >>>
>> >>> 2. It's short - variants with using model for that will look much
>> longer,
>> >>> when
>> >>> joining two or more filters:
>> >>>
>> >>> >>> GameSession.objects.user.profile_last_login_date >= yesterday #
>> >>> >>> awkward
>> >>>
>> >>> 3. Implementation will not require to change querset manager or model
>> >>> classes
>> >>>
>> >>> 4. Will still allow to use filters and Q class in the old way:
>> >>>
>> >>> >>> q = Q(user__profile__last_login_date__gte=yesterday)
>> >>>
>> >>> or
>> >>>
>> >>> >>>
>> >>> >>>
>> GameSession.objects.filter(user__profile__last_login_date__gte=yesterday)
>> >>>
>> >>> I'd like to make it as a part of Django ORM syntax and it will not be
>> >>> hard to
>> >>> do, especially taking into account the library is already done and
>> >>> working.
>> >>> Anyway, I need your thought about the idea in general, as well as
>> about
>> >>> particular things like chosen method names - "get_path", "in_range"
>> and
>> >>> etc.
>> >>> As next step I can create a ticket in the issue tracker, or prepare
>> DEP
>> >>> first.
>> >>> In latter case I need to find a shepherd to work with.
>> >>>
>> >>> Best regards,
>> >>> Alexey
>> >
>> > --
>> > You received this message because you are subscribed to the Google
>> Groups
>> > "Django developers (Contributions to Django itself)" group.
>> > To unsubscribe from this group and stop receiving emails from it, send
>> an
>> > email to django-develop...@googlegroups.com.
>> > To post to this group, send email to django-d...@googlegroups.com.
>> > Visit this group at http://groups.google.com/group/django-developers.
>> > To view this discussion on the web visit
>> >
>> https://groups.google.com/d/msgid/django-developers/3bad8371-f9b4-47ff-a681-0108b320e9b5%40googlegroups.com.
>>
>>
>> >
>> > For more options, visit https://groups.google.com/d/optout.
>>
>
--
You received this message because you are subscribed to the Google Groups
"Django developers (Contributions to Django itself)" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to django-developers+unsubscr...@googlegroups.com.
To post to this group, send email to django-developers@googlegroups.com.
Visit this group at http://groups.google.com/group/django-developers.
To view this discussion on the web visit
https://groups.google.com/d/msgid/django-developers/5e7ee87b-6253-420b-9688-51c39d657cab%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.
