Re: follow relationship

[Ned Batchelder]

What I've done in these cases is to define a Constants class:     class Constants:         """ Construct one of these with keyword arguments, and you can use the             attributes.         """         def __init__(self, **kwargs):             for k, v in kwargs.items():                 setattr(self, k, v)         def choices(self):             return list(self.__dict__.items()) (I guess Enumeration would be a better name), then I can define a list of constants:     kBranchKind = Constants(         main = 1,         aux = 2,         dead = 3     ) Then in the code, you can use kBranchKind.dead, and in your model, you can use: class Branch(meta.Model): trunk = meta.ForeignKey(Trunk) kind = meta.IntegerField(choices=kBranchKind.choices()) It keeps the list of choices in one place, gives you run-time errors if you mistype the constant name (string literals would not), and it works just as well with strings for the values. --Ned. Ivan Sagalaev wrote: Todd O'Bryan wrote: Your comment at the end got me thinking, though. Writing trunk.get_branch(kind__exact=2) is not very illuminating, but you're correct that the value 'Dead' could get changed later. In Java, I'd use constants for the integer values public static final int DEAD = 2; but that seems to violate DRY, because the semantics is already listed in the choices list. I like using integers for what end up being enumerated types because they don't take much space in the database and, as you mentioned, it's easy to change the English version without having to do anything to the db representation. Is there a better way to do this kind of thing? This got me thinking too :-) Generally when I need a constant in Python I don't hesitate to use string values for constants which are both values and names. So I'd have BRANCH_KINDS = (('main', 'Main'), ('aux', 'Auxiliary'), ('dead', 'Dead'),) I think it won't even hurt performance in DB lookups if you create index for this field. However this implies changing the field to CharField which won't become a <select> box in admin and in automatic manipulators (if I'm not mistaken). A lookup table for branch kinds would solve this: class BranchKind(meta.Model): id = meta.SlugField(primary_key=True) title = meta.CharField(maxlength=50) You can then do something like trunk.get_branch(pk='dead') . -- Ned Batchelder, http://nedbatchelder.com --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to django-users@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/django-users -~----------~----~----~----~------~----~------~--~---