query join tables

[dk]

I have this 2 models

class Choice(models.Model):
    restaurant = models.ForeignKey(Restaurant)
    person = models.ForeignKey(Person)
    date = models.DateField("time published")
    time = models.TimeField("date published")

class Person(models.Model):
    name = models.CharField(max_length=100)
    last_name = models.CharField(max_length=100)
    email = models.EmailField()

and I would like to be able to see check if in a certain date, a certain person does exist in the record.

I am currently querying the date first.

date_query = Choice.objects.filter(date=dater)
for i in date_query:
    if i.person_id == to_email_i_am_looking:

might be another way to chain the querys?

kinda

SELECT person  FROM choice JOIN people
ON choice.person_ID=person+ID;

WHERE date= today and person=someone

?

I read about select_related that use the ForeignKey,  but I have 2 in my case,  the person and the restaurant,  does it loop on bouth?

[Tom Lockhart]

On Oct 12, 2014, at 10:01 PM, dk <dem...@gmail.com> wrote:

I have this 2 models

class Choice(models.Model):
    restaurant = models.ForeignKey(Restaurant)
    person = models.ForeignKey(Person)
    date = models.DateField("time published")
    time = models.TimeField("date published")

class Person(models.Model):
    name = models.CharField(max_length=100)
    last_name = models.CharField(max_length=100)
    email = models.EmailField()

and I would like to be able to see check if in a certain date, a certain person does exist in the record.

I am currently querying the date first.

date_query = Choice.objects.filter(date=dater)
for i in date_query:
    if i.person_id == to_email_i_am_looking:

might be another way to chain the querys?

You can chain together the filters:

person = Person.objects.get(name=person_name)

choices_for_person_on_date = Choice.objects.filter(date=dater).filter(person=person)

hth

- Tom

[dk]

I will give a try,   how does django know that have to join  using double filter? or it just auto-magically knows behind the hood?

or filtering by another model/class django get the idea, and joins the tables?

Thanks Tom =)

[Anderson]

HI there..

Looks like you already have the person ID , you don't need hit the database every time  to call Person object.

You can make faster only check for ID not Person object.

instead this:

person = Person.objects.get(name=person_name)

choices_for_person_on_date = Choice.objects.filter(date=dater).filter(person=person)

You can do this

choices_for_person_on_date = Choice.objects.get(date=dater,person_id = to_email_i_am_looking)

and if you want the joins

Choice.objects.get(date=dater,person_id = to_email_i_am_looking).select_related('person')

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[Jani Tiainen]

You can leverage reverse relation managers rather easily:

If you do have a person available already you can do the following:

choices_for_person_on_date = person.choice_set.filter(date=dater)

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Jani Tiainen