Newbie : Object copy - weird error :-)

[mickae...@gmail.com]

Hi all :-)

I'd like to archive some data.

I did that :

class AbstractDataModel(models.Model):

xxx


class Meta:
        abstract = True


def __iter__(self):

        return iter([self.xxx, self.yyy, self.zzz, self.aaa,
            self.qqq, self.mode_bbb])


class DataModel(AbstractDataModel):


pass


class DataModelArchive(AbstractDataModel):
    # https://stackoverflow.com/questions/21699707/python-how-to-copy-all-attibutes-from-base-class-to-derived-one
    def __init__(self, source=None):
        if source is not None:
            self.__dict__.update(source.__dict__)

But when I want to access data in DataModelArchive, like DataModelArchive.objects.all() for example,
I get

Traceback (most recent call last):
  File "/home/.../tests.py", line 1090, in test_archive
    print(DataModelArchive.objects.all())
  File "/home/.../venv/lib/python3.6/site-packages/django/db/models/query.py", line 248, in __repr__
    data = list(self[:REPR_OUTPUT_SIZE + 1])
  File "/home/.../venv/lib/python3.6/site-packages/django/db/models/query.py", line 272, in __iter__
    self._fetch_all()
  File "/home/.../venv/lib/python3.6/site-packages/django/db/models/query.py", line 1179, in _fetch_all
    self._result_cache = list(self._iterable_class(self))
  File "/home/.../venv/lib/python3.6/site-packages/django/db/models/query.py", line 63, in __iter__
    obj = model_cls.from_db(db, init_list, row[model_fields_start:model_fields_end])
  File "/home/.../lib/python3.6/site-packages/django/db/models/base.py", line 507, in from_db
    new = cls(*values)
TypeError: __init__() takes from 1 to 2 positional arguments but 11 were given

What am I doing wrong ?

Thx

;-)

[赖信桃]

Can you format your code or post it on a gist?

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[Julio Biason]

Hi Mikael,

The problem is happening because of this: __init__() takes from 1 to 2 positional arguments but 11 were given

On your new __init__(), you added just 2 parameters: `self` and `source`. But you overwrote the default `models.Model` init, which receives way more parameters (the original signature for this function is `__init__(self, *args, **kwargs)`).

What are you actually trying to achieve with this?

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[Mickael Barbo]

Hi 赖信桃,

Sorry for formating problem. Here it is

class AbstractDataModel(models.Model):

    xxx


    class Meta:
        abstract = True


    def __iter__(self):

         return iter([self.xxx, self.yyy, self.zzz, self.aaa,
              self.qqq, self.mode_bbb])


class DataModel(AbstractDataModel):

    pass


class DataModelArchive(AbstractDataModel):
    # https://stackoverflow.com/questions/21699707/python-how-to-copy-all-attibutes-from-base-class-to-derived-one
    def __init__(self, source=None):
        if source is not None:
            self.__dict__.update(source.__dict__)

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[Mickael Barbo]

Hello  Julio,

Ok, I see.

I try to create a way to archive (copy) the same object instance on an other DataBase.

I followed this advice : # https://stackoverflow.com/questions/21699707/python-how-to-copy-all-attibutes-from-base-class-to-derived-one


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[Melvyn Sopacua]

On vrijdag 29 juni 2018 09:44:40 CEST Mickael Barbo wrote:

 

> I try to create a way to archive (copy) the same object instance on an

> other DataBase.

>

> I followed this advice : # https://stackoverflow.com/

> questions/21699707/python-how-to-copy-all-attibutes-from-

> base-class-to-derived-one

 

That advice is for normal python classes. Django models have some restrictions, one being that fields are special attributes. Messing with a model's __init__() is not something you normally do as a model's class creation is highly customized.

 

If you're really using 2 different databases, a model's save() operation supports a `using` keyword that allows you to select the database connection. Archiving becomes really easy that way.

 

 

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Melvyn Sopacua

[mickae...@gmail.com]

Thanks you Melvyn, this is it :-)

Have a nice day.

Regards