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

我有一个设置了 max_length 的字段.当我保存一个模型实例，并且该字段的值大于 max_length 时，Django 会在数据库级别强制使用 max_length.(参见关于模型的 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)

但是，由于我使用的是 Postgres，我收到了这样的 DatabaseError 异常:

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

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

我更喜欢自动截断值(所以我没有例外).现在，我可以手动执行此操作，但我真正想要的是让我的所有模型自动截断该值.(不一定是智能的.只需在第 999 个字符处将其切断即可.)

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.)

我是否应该编写一个从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?这似乎不雅，必须有更好的方法.

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

您可以创建一个自动截断字段的自定义字段(我认为此代码应该可以工作，但请仔细检查):

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，您无需在 models.py 文件中使用 models.CharField，而只需使用 TruncatingCharField.

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

get_prep_value 为要插入数据库的字段准备值，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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