我有一個簡單的自定義字段實現利用Python 3枚舉實例。將枚舉實例分配給我的模型屬性,並保存到數據庫可正常工作。但是,使用QuerySet獲取模型實例會導致enum屬性是一個字符串,而不是相應的Enum實例。自定義Django字段不返回來自查詢的枚舉實例
如何獲取下面的EnumField
以返回有效的Enum
實例,而不是字符串?
fields.py:
from enum import Enum
from django.core.exceptions import ValidationError
from django.db import models
class EnumField(models.CharField):
description = 'Enum with strictly typed choices'
def __init__(self, enum_class, *args, **kwargs):
self._enum_class = enum_class
choices = []
for enum in self._enum_class:
title_case = enum.name.replace('_', ' ').title()
entry = (enum, title_case)
choices.append(entry)
kwargs['choices'] = choices
kwargs['blank'] = False # blank doesn't make sense for enum's
super().__init__(*args, **kwargs)
def deconstruct(self):
name, path, args, kwargs = super().deconstruct()
args.insert(0, self._enum_class)
del kwargs['choices']
return name, path, args, kwargs
def from_db_values(self, value, expression, connection, context):
return self.to_python(value)
def to_python(self, value):
if value is None or isinstance(value, self._enum_class):
return value
else:
return self._parse_enum(value)
def _parse_enum(self, value):
try:
enum = self._enum_class[value]
except KeyError:
raise ValidationError("Invalid type '{}' for {}".format(
value, self._enum_class))
else:
return enum
def get_prep_value(self, value):
if value is None:
return None
elif isinstance(value, Enum):
return value.name
else:
msg = "'{}' must have type {}".format(
value, self._enum_class.__name__)
if self.null:
msg += ', or `None`'
raise TypeError(msg)
def get_choices(self, **kwargs):
kwargs['include_blank'] = False # Blank is not a valid option
choices = super().get_choices(**kwargs)
return choices