help with foreignkeys

[psychok7]

so i have this 2 models (Comment and Park)

Comment has a foreign key to USER and PARK

PARK has a foreign key to Comment

my question is, isn't there going to be a deadlock if i don't have a comment or a park created? i mean , in order to create a Park i need to have a comment, and in order to create a comment i need a park and a user.

is there a way for me to fix my problem? like allowing the foreign key to be null or something like that?

thanks in advance

[jondykeman]

As far as I understand it the ForeignKey will have to be unique=True and null=False.

I want to get a better sense of what you are trying to achieve. Is it that you want to link comment and park only some of the time?

JD

[psychok7]

yes, like a park doesn't have to have comments, but all the comments must have an associated park and user all the time.

what is the django syntax for me to achieve this?

[jondykeman]

If all comment have to have a park and user. 

I would have a ForeignKey to Park and User in the Comments model, and no Foreign key in the Parks model.

As such a comment will always need to be linked to an existing park and user object, but a park can be created without needing a comment.

JD

[psychok7]

i think you are right :) , i can always get the parks associated comments if i query comments model (im used to only doing it the other way around). gonna try that out

thanks

[Nikolas Stevenson-Molnar]

When you have a FK to park in your comment model, you automatically get a reference to a list of comments from the park model. E.g:

class Park(models.Model):

#Park fields here, but no explicit relationship to Comment

class Comment(models.Model):

park = models.ForeignKey(Park)

#other comment fields here

def some_view(request, id):

park = Park.objects.get(pk=id)

comments = park.comment_set #this is a queryset of all comments associated with the part; it may be empty

#etc...

Or in a template:

{% for comment in park.comment_set.all %}

   {{ comment.body }}

{% endfor %}

Does that make sense? Here are the official docs for this functionality: https://docs.djangoproject.com/en/dev/topics/db/queries/#related-objects

_Nik

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[psychok7]

thanks thats exactly wht i needed ;)

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