在Django CharFields中以max_length自动截断字段 [英] Auto-truncating fields at max_length in Django CharFields

问题描述

我有一个 max_length 集合的字段。当我保存模型实例时，字段的值大于 max_length ，Django在数据库级别强制执行 max_length 。 （有关模型，请参阅Django文档： http ：//docs.djangoproject.com/en/dev/ref/models/fields/#django.db.models.CharField.max_length ）

I have a field that has a max_length set. When I save a model instance, and the field's value is greater than max_length, Django enforces that max_length at the database level. (See Django docs on models: http://docs.djangoproject.com/en/dev/ref/models/fields/#django.db.models.CharField.max_length)

然而因为我使用Postgres，所以我收到一个 DatabaseError 这样的异常：

However, since I am using Postgres, I receive a DatabaseError exception like this:

DatabaseError: value too long for type character varying(1000)

截断值（所以我没有异常）。现在，我可以手动执行，但我真正想要的是让我的所有模型自动截断值。 （不一定是智能的，只需在第999个字符处切掉它就可以了。）

I would prefer to instead auto-truncate the value (so I don't have an exception). Now, I can do this manually, but what I would really want is to have all of my models auto-truncate the value. (Not necessarily intelligently. Just cutting it off at the 999th character is fine.)

我应该写一个从models.Model导入的自定义类，并覆盖save ）方法，循环遍历每个_meta.field，检查max_length，然后截断？

Should I just write a custom class that imports from models.Model and override the save() method, looping through each _meta.field, checking for the max_length, and then truncating? That seems inelegant and there must be a better way.

推荐答案

您可以创建自动截断字段的自定义字段（I认为这个代码应该工作，但是仔细检查一下）：

You could create a custom field that auto-truncates the field (I think this code should work, but double-check it):

class TruncatingCharField(models.CharField):
    def get_prep_value(self, value):
        value = super(TruncatingCharField,self).get_prep_value(value)
        if value:
            return value[:self.max_length]
        return value

然后，而不是使用 models.CharField 您的 models.py 文件，您只需使用TruncatingCharField。

Then, instead of using models.CharField in your models.py file, you'd just use TruncatingCharField instead.

get_prep_value 准备值对于要在数据库中插入的字段，因此它是截断的理想位置。

get_prep_value prepares the value for a field for insertion in the database, so it's the ideal place to truncate.

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