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-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/ceeb43c7-b44f-4e81-bd8f-5997df9edb43%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.