如何处理“SubfieldBase已被弃用”。请改用Field.from_db_value。“ [英] How to deal with "SubfieldBase has been deprecated. Use Field.from_db_value instead."

问题描述

在升级到Django 1.9时，我现在收到警告。

On upgrade to Django 1.9, I now get the warning

RemovedInDjango110Warning: SubfieldBase has been deprecated. Use Field.from_db_value instead.

我看到问题出现在哪里。我有一些自定义字段定义，在其中我有 __ metaclass__ = models.SubfieldBase 。例如，

I see where the problem arises. I have some custom field definitions, and in them I have __metaclass__ = models.SubfieldBase. For example,

class DurationField(models.FloatField):

    __metaclass__ = models.SubfieldBase

    def __init__(self, *args, **kwargs):

    ...

如果 __元类__ 语句已被弃用，我应该将其替换为什么？

If the __metaclass__ statement is deprecated, what am I supposed to replace it with exactly?

我只是拿出来，添加一个 from_db_value 方法，如下例所示： https://docs.djangoproject.com/en /1.9/howto/custom-model-fields/#converting-values-to-python-objects
？

Do I just take it out and add a from_db_value method like in the example here: https://docs.djangoproject.com/en/1.9/howto/custom-model-fields/#converting-values-to-python-objects ?

而且$ code> from_db_value 和 to_python 不同？两者似乎将数据库数据转换成Python对象？

And how are from_db_value and to_python different? The both seem to convert database data to Python objects?

推荐答案

是的，你应该删除 __ metaclass __ 行，并添加 from_db_value（）和 to_python（）：

Yes, you should just remove __metaclass__ line and add from_db_value() and to_python():

class DurationField(models.FloatField):

    def __init__(self, *args, **kwargs):
        ...

    def from_db_value(self, value, expression, connection, context):
        ...

    def to_python(self, value):
        ...

如下所述： https://docs.djangoproject.com/en/1.9/ref/models/fields/#field-api-reference ， to_python（value）将值（可以是无，字符串或对象）转换为正确的Python对象。

As described here: https://docs.djangoproject.com/en/1.9/ref/models/fields/#field-api-reference, to_python(value) converts the value (can be None, string or object) into the correct Python object.

from_db_value（value，expression，connection，context）将数据库返回的值转换为Python对象

from_db_value(value, expression, connection, context) converts a value as returned by the database to a Python object.

所以，这两种方法都返回Python对象，但Django在不同的情况下使用它们。通过反序列化和在表单中使用的 clean（）方法调用 to_python（）。 $ code> from_db_value（）在从数据库加载数据时调用

So, both methods return Python objects, but they are used by Django in different situations. to_python() is called by deserialization and during the clean() method used from forms. from_db_value() is called when the data is loaded from the database

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