RE: [] Re: Combining queries? A "join" in Python?

Yes, you can - but not in models.py!
I have created a query.py and defined all models for raw queries in that file.
Then I do raw SQL as defined here:
https://docs.djangoproject.com/en/dev/topics/db/sql/

But you won't be able to update/insert data using this models.

regards

H.

>reply to message:
>date: 30.08.2011 02:02:13
>from: "graeme" <graeme.pietersz@gmail.com>
>to: "Django users" <django-users@googlegroups.com>
>subject: [<django-users.googlegroups.com>] Re: Combining queries? A "join" in Python?
>
>
>
>On Aug 30, 6:25 am, Tim <timothyp...@gmail.com> wrote:
>> worst case you could always just write the sql query?
>>
>> https://docs.djangoproject.com/en/dev/topics/db/sql/
>>
>
>I have been looking at that already, what I have not yet figured out
>is how the results map to models if I do a join in the SQL query. Can
>it create the models for the joined tables as well?
>
>> On Aug 29, 8:15 am, graeme <graeme.piete...@gmail.com> wrote:
>>
>>
>>
>>
>>
>>
>>
>> > I looks like my attempt to simplify and abstract the problem just made
>> > it harder to help me: my apologies for that. I was trying to combined
>> > two different problems rather than ask two questions. Thanks for
>> > helping despite that.
>>
>> > I think I have a solution for most of my problems, as far as getting
>> > the queries working. I might be back with questions about
>> > optimisation, but I can live with a little inefficiency in the query I
>> > need to get working first.
>>
>> > On Aug 28, 4:33 am, Matteius <matte...@gmail.com> wrote:
>>
>> > > Since you are combining two sets of different objects you'll want
>> > > Gelonida's response.  Additionally, Use Q to create more logically
>> > > advanced queries.  I find your language difficult to gather what query
>> > > you are looking for exactly, but here is an example of what I think
>> > > you might mean:
>>
>> > > from django.db.models import Q
>>
>> > > the_Ds = D.objects.all().filter(b=B)
>> > > the_Es = E.objects.all().filter(c=C)
>>
>> > > combined = the_Ds | the_Es
>>
>> > > # Other Example (an & requires both constraints to be met, and an Or
>> > > will include the set of all matches.
>> > > the_As = A.objects.all().filter(Q(constraint1) & Q(constraint2))
>> > > the_Bs = B.objects.all().filter(Q(constraint1) | Q(constraint2))
>>
>> > > -Matteius
>>
>> > > Don't overlook how powerful this is because Django has Manager classes
>> > > so you can make your constraints refer to both local properties and
>> > > foreign key constraints as well as properties within the foreign key
>> > > lookups.  You may find that you wish to edit your schema relationship,
>> > > perhaps by pointing backwards or reversing the relationship.  It is
>> > > hard to say with the categorical A, B, C, D example, but hope this
>> > > helps and Good Luck!
>>
>> > > On Aug 27, 3:47 pm, Gelonida N <gelon...@gmail.com> wrote:
>>
>> > > > On 08/27/2011 11:39 AM, graeme wrote:
>>
>> > > > > I have a some models related link this:
>>
>> > > > > A has a foreign key on B which has a foreign key on C
>>
>> > > > > I also have D with a foreign key on B, and E with a foreign key of C
>>
>> > > > > If I do A.filter(**args).select_related() I will get all the As, Bs,
>> > > > > and Cs I want.
>>
>> > > > > How do I get the Ds with a foreign key on a B in my queryset
>> > > > > (preferably filtered) and all Es with a foreign key on C (also
>> > > > > preferably filtered)
>>
>> > > > > The best I have been able to come up with is to query for all the  the
>> > > > > Ds and Es I want, and combine them with the Bs and Cs in the view
>>
>> > > > > I have a similar problem with another site, except that there not
>> > > > > every B I want has an A with a foreignkey pointing to it, so I cannot
>> > > > > just do select_related on A.
>>
>> > > > > I am not worried about doing an extra query or two per page. What I
>> > > > > want to avoid is doing an extra query for each object in a lengthy
>> > > > > list.
>>
>> > > > You can 'or' two query sets with the '|' operator
>>
>> > > > so do
>> > > > queryset1 = Mymodel.objects.all().filter(...)
>> > > > qyeryset2 = Mymodel.objects.all().filter(...)
>>
>> > > > combined = queryset1 | queryset2
>
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