Re: Comparing two ManyToMany fields for same entries

I'm going to guess that my version is slow since a new query would be run
for each row returned by the initial one.

Check out an app called django-debug-toolbar. It has a view that will
show you all of the SQL queries generated as a page is built. It will
also tell you how long each query took to run. This should allow you to
compare the three methods.

Brett

On 10/28/11 1:44 PM, "Kevin" <kveroneau@gmail.com> wrote:

>I think the filter I used does work to detect related friends, here is
>a Pythonic example of the same code, but done differently without
>filters:
>
>Person.objects.get(name='Person1').friends.get().friends.all()
>
>Instead of returning back 'Person1', when using filters, this returns
>back 'Person0'.
>
>Person.objects.get(name='Sean').friends.get().friends.get(name='Person0')
>
>My next question, which would be better optimized for database hits:
>
>* Brett's example
>* using the filter version
>* using the Pythonic version, but use select_related(depth=2) option?
>
>I am trying to make sure the database hits are optimized as this will
>be queries multiple times per page hit for different models. Also,
>which would be faster to make sure the page loads are not burden when
>lots of these types of queries go through?
>
>Thanks.
>
>On Oct 28, 1:34 pm, Kevin <kveron...@gmail.com> wrote:
>> Thanks. Is this way good for database optimization though? I guess I
>> could use select_related(). I was hoping there was a QuerySet I could
>> run.
>>
>> I made this one, although I'm not sure if it works correctly:
>>
>>
>>Person.objects.filter(name='Person1').filter(friends__friends__name='Pers
>>on0')
>> This outputs "Person1", if I interchange Person0 with Person2, it
>> outputs no results. If I use Person1 in both instances, it outputs
>> 'Person1'.
>> Does this QuerySet return the results I want, or should I use Brett's
>> suggestion?
>>
>> Thanks again.
>>
>> On Oct 28, 1:21 pm, Brett Epps <Brett.E...@quest.com> wrote:
>>
>> > Try this:
>>
>> > for friendof0 in Person0.friends.all():
>> > for friendof1 in Person1.friends.all():
>> > if friendof0 == friendof1:
>> > # Person 0 and Person 1 share a friend.
>> > else:
>> > # They have no shared friends.
>>
>> > Brett
>>
>> > On 10/28/11 12:59 PM, "Kevin" <kveron...@gmail.com> wrote:
>>
>> > >Just thought I'd add another example using Python script:
>>
>> > >Person0 = Person()
>> > >Person1 = Person()
>> > >Person2 = Person()
>> > >Person0.friends.add(Person2)
>> > >Person2.friends.add(Person0)
>> > >Person2.friends.add(Person1)
>> > >Person1.friends.add(Person2)
>>
>> > >Now, I would like to do the following, but it seems to fail:
>>
>> > >Person0.friends.all() in Person1.friends.all(). I would like it to
>> > >say if Person0 and Person1 share another friend in common.
>>
>> > >Person0 and Person2 are friends
>> > >Person1 and Person2 are friends
>> > >Person0 and Person1 are NOT friends, but share a friend in common.
>> > >How does one find out that even though Person0 and Person1 are not
>> > >friends, they do share Person2 as a friend.
>>
>> > >I can use my eye on a Python shell to see that Person2 exists on both
>> > >Peson0 and Person1, but how does one make the code see it?
>>
>> > >Sorry for having to clarify this so much, I'm just not sure that my
>> > >last post actually explained it properly.
>>
>> > >Thanks.
>>
>> > >On Oct 28, 12:30 pm, Kevin <kveron...@gmail.com> wrote:
>> > >> Hello,
>>
>> > >> I am building a model which shares a relation with another model
>> > >> using a ManyToManyField. What I need to do, is find out which
>>models
>> > >> are on both on two seperate ManyToManyField lists. Here is a
>>simple
>> > >> example of what I am trying to do:
>>
>> > >> Person:
>> > >> friends=ManyToManyField(self)
>>
>> > >> To find out this persons direct friends, Person.friends...
>> > >> To find out which friends this Person shares in common with another
>> > >> Person, ????
>>
>> > >> Person0:
>> > >> Person1
>> > >> Person6
>> > >> Person3
>> > >> Person8
>>
>> > >> Person1:
>> > >> Person2
>> > >> Person6
>>
>> > >> What would be the most optimized QuerySet to find out that both
>> > >> Person0 and Person1 are both friends with Person6?
>>
>> > >> Is there a specific Django app perhaps that can ease develop of
>>this
>> > >> type of data relations between objects?
>>
>> > >> Thanks.
>>
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