Values from class to class

[Carlos Andre]

Hello to all , I need to solve a problem. I have two classes of which have to use , in the second class, the first coming values. How to do this?
Thanks for listening!

[James Schneider]

Can you give a simple example or analogy of what you are trying to do?

-James

On Jul 6, 2015 5:29 PM, "Carlos Andre" <euca...@gmail.com> wrote:

Hello to all , I need to solve a problem. I have two classes of which have to use , in the second class, the first coming values. How to do this?
Thanks for listening!

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[Carlos Andre]

example : I have two classes, respectively person contact.
I want to contact class has , in its attributes , values ​​worked coming from class person , such as name, pass in person , and size of the contact name in the class.
I did something like this :
from django.db import models

class person ( models.Model ) :
    qtdade = models.IntegerField (default = 1 )

    class Meta :
        verbose_name_plural = ' Person '

    def valor_contato ( self):
        return self.qtdade * 2

class contact ( models.Model ) :
    p = Person ()
    value = models.CharField ( max_length = 150, default = p.qtdade )

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[James Schneider]

On Tue, Jul 7, 2015 at 10:59 AM, Carlos Andre <euca...@gmail.com> wrote:
> example : I have two classes, respectively person contact.
> I want to contact class has , in its attributes , values worked coming from
> class person , such as name, pass in person , and size of the contact name
> in the class.

Ahh, what you probably want is a foreign key relationship from Contact
back to Person. See below.

I'm not sure what you mean by size, though. Is that a reference to the
qtdade field?

> I did something like this :
> from django.db import models
>
> class person ( models.Model ) :
> qtdade = models.IntegerField (default = 1 )
>
> class Meta :
> verbose_name_plural = ' Person '
>
> def valor_contato ( self):
> return self.qtdade * 2
>
> class contact ( models.Model ) :
> p = Person ()
> value = models.CharField ( max_length = 150, default = p.qtdade )
>

What you probably want is this:

class Contact( models.Model ) :
p = models.ForeignKey(Person, null=False)


Note that I used an uppercase letter to start your class (Contact).
Python classes in general use the CapWords naming convention. See PEP8
(https://www.python.org/dev/peps/pep-0008/#class-names).

This makes the Person attributes available via the Contact model
class, so you can do something like this:

a_person = Person.objects.create(qtdade=3)

a_contact = Contact.objects.create(p=a_person)

print(a_contact.p.qtdade)

##########
# Would print out 3
##########

Any attributes that are added to the Person class would then be
available to a Contact using the syntax I set above. See the
documentation on relationships between models:

https://docs.djangoproject.com/en/dev/topics/db/models/#many-to-one-relationships

As far as this line goes:

> value = models.CharField ( max_length = 150, default = p.qtdade )

It looks like you are trying to set a default in the model definition
that is dependent on a field in another model. Django doesn't support
this because this is a single value that is applied directly in the
database on the column during a migration/database initialization
(therefore, no objects exist in order to determine what that value
should be on a fresh migration). In general, you would set such a
value inside of the save() method for your model whenever a Contact is
saved, and use default='' (or default=None, but not recommended for
CharField fields) in the model definition above.

See this link for more information regarding the save() method on models:

https://docs.djangoproject.com/en/dev/topics/db/models/#overriding-predefined-model-methods

[Carlos Andre]

i trying use thats solutions, in real yet continuos the problem.

The value, when are to use in other class, return to defaut value without get the value who i send in the field.

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[Carlos Andre]

I want copy some values to other fields in other table!

[James Schneider]

On Tue, Jul 7, 2015 at 4:31 PM, Carlos Andre <euca...@gmail.com> wrote:
> I want copy some values to other fields in other table!
>

That's fine, although I would only recommend doing so if the qtdade in
Person and 'value' field in Contact can contain different data in some
scenario. You will still need to set a static default (ie default='')
in the model definition and override the save() method to do the copy,
though:

# This is a bit naive and assumes that p always contains a Person
object. Add validation and/or business logic accordingly.

def save(self, *args, **kwargs):
# If no PK, we know this is a new object and that value hasn't been set
if not self.pk:
self.value = self.p.qtdade
super(Contact, self).save(*args, **kwargs) # Call the "real" save() method.


If they will always be the same, I would recommend keeping the
approach that I sent out originally, and in addition, adding a
property or model method to retrieve that data in the Contact class.

-James