CODEWITHSUNDEEP
pythondjangoinheritancedjango-modelsabstract
Sashko Lykhenko
Sashko Lykhenko

Reputation: 1664

How to write common implementation of __str__ method for all my models in Django?

I want all my models to override __str__ method in similar fashion:

class MyModel1(models.Model):
    name = models.CharField(max_length=255)

    def __init__(self):
        self.to_show = 'name'

    def _show(self):
        if hasattr(self,self.to_show):
            return str(getattr(self, self.to_show))
        else:
            return str(getattr(self, 'id'))

    def __str__(self):
        return self._show()

class MyModel2AndSoOn(models.Model):
    another_param = models.CharField(max_length=255)
    # same implementation of `__str__` but with another_param

I do not want to repeat the same code for all my models so I tried inheritance:

class ShowModel(models.Model):
    name = models.CharField(max_length=255)

    def __init__(self):
        self.to_show = 'name'

    def _show(self):
        if hasattr(self,self.to_show):
            return str(getattr(self, self.to_show))
        else:
            return str(getattr(self, 'id'))

    def __str__(self):
        return self._show()

class MyModel1(ShowModel):
    another_param = models.CharField(max_length=255)

class MyModel2(ShowModel):
    another_param = models.CharField(max_length=255)

but it messes with id of MyModel1 and MyModel2 by replacing id with a pointer to ShowModel. How to write common implementation of __str__ method for my models without inheritance or how to prevent treating ShowModel class as a Django model?

Upd: I used abstract model as alecxe suggested but it ended with an error message:

in _show
    return str(getattr(self, self.to_show))
File "/path/to/my/project/env3/lib/python3.5/site-packages/django/db/models/fields/__init__.py", line 188, in __str__
model = self.model
AttributeError: 'CharField' object has no attribute 'model'

Upd Everything works fine if I assign value to the name field of my model object. Whole solution:

class ShowModel(object):
    to_show = 'name'

    def _show(self):
            if hasattr(self,self.to_show):
                return str(getattr(self, self.to_show))
            elif hasattr(self,'id'):
                return str(getattr(self, 'id'))
            else:
                return str(self)

    def __str__(self):
         return self._show()

    class Meta:
        abstract = True

class MyModel1(ShowModel):
    name = models.CharField(max_length=255)
    to_show = 'name'

class MyModel2(ShowModel):
    another_param = models.CharField(max_length=255)
    to_show = 'another_param'

in test case:

ua = MyModel1()
ua.name = 'hi'
print(ua)
#prints hi

ub = MyModel2()
ub.another_param = 'hi again'
print(ub)
#prints hi again

Upvotes: 3

Views: 1659

Answers (1)

alecxe
alecxe

Reputation: 474031

You need to create an abstract model:

class ShowModel(models.Model):
    name = models.CharField(max_length=255)

    def __init__(self):
        self.to_show = 'name'

    def _show(self):
        if hasattr(self, "to_show"):
            return str(getattr(self, "to_show"))
        else:
            return str(getattr(self, 'id'))

    def __str__(self):
        return self._show()

    class Meta:
        abstract = True

And, as for your follow-up question and thanks to @itzmeontv, you should replace self.to_show with "to_show" when calling hasattr() and getattr().

Upvotes: 1

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