Django: Dynamic model field definition

问题

Hi Stackoverflow people,

I have a model definition which is rather monotone, it includes fields for bins from 1 to 50.

For the proof of concept, I wrote it by hand, but there must be a better way to automate the model definition and to keep the code nice and tidy.

So far I did it the follow way:

class Bins(models.Model):
    p1 = models.DecimalField(_('bin 1'), max_digits=6, decimal_places=2)
    p2 = models.DecimalField(_('bin 2'), max_digits=6, decimal_places=2)
    p3 = models.DecimalField(_('bin 3'), max_digits=6, decimal_places=2)
    ...
    p50 = ...

On the Django wiki, I found a summary for dynamic model definitions, but its seems that it does not allow for loops in the definition:

I have tried the code below, but I get an error msg that MAX_BIN = 2 is an invalid syntax. I understand the error that I can't iterated over the field like I tried.

Bins = type('Bins', (models.Model,), {     
    MAX_BIN = 50
    for i in range(MAX_BIN):
        name_sects = ["p", str(i)]
        "".join(name_sects): model.DecimalField(_("".join([bin ', str(i)])),
                             max_digits=6, decimal_places=2)
    })

Is such a dynamic class definition generally possible? If so, what is the best way to define the class?

Thank you for your help!

回答1:

in your current edition, your loop is inside the definition of a dict. that's not allowed. however, you could define your fields in a dict outside your call to type which works fine. something like

attrs = {
    other_field = models.IntegerField(),
    '__module__': 'myapp.models',
}

MAX_BIN = 50
   for i in range(MAX_BIN):
       name_sects = ["p", str(i)]
        attrs["".join(name_sects)] = model.DecimalField(_("".join(['bin ', str(i)])),
            max_digits=6, decimal_places=2)

Bins = type('Bins', (models.Model,), attrs)

回答2:

A simple solution that solves the same issue:

class Bins(models.Model):
    MAX_BIN = 50
    for i in xrange(1, MAX_BIN + 1):
        vars()['p' + str(i)] = models.DecimalField('bin ' + str(i),
            max_digits=6, decimal_places=2)

来源：https://stackoverflow.com/questions/8276046/django-dynamic-model-field-definition