軟刪除介紹

簡單的說董习，就是當(dāng)執(zhí)行刪除操作的時候枫慷，不真正執(zhí)行刪除操作丑念，而是在邏輯上刪除一條記錄涡戳。這樣做的好處是可以統(tǒng)計數(shù)據(jù)，可以進(jìn)行恢復(fù)操作等等脯倚。
Managers 是django models 提供的一個用于提供數(shù)據(jù)庫查詢操作的接口渔彰，對于Django應(yīng)用程序中的每個model都會至少存在一個Manager
詳細(xì)：https://docs.djangoproject.com/zh-hans/3.2/topics/db/managers/

django實(shí)現(xiàn)軟刪除model

from django.db import models
from django.db.models.query import QuerySet

# 自定義軟刪除查詢基類

class SoftDeletableQuerySetMixin(object):
    """
    QuerySet for SoftDeletableModel. Instead of removing instance sets
    its ``is_deleted`` field to True.
    """
    def delete(self):
        """
        Soft delete objects from queryset (set their ``is_deleted``
        field to True)
        """
        self.update(is_deleted=True)


class SoftDeletableQuerySet(SoftDeletableQuerySetMixin, QuerySet):
    pass


class SoftDeletableManagerMixin(object):
    """
    Manager that limits the queryset by default to show only not deleted
    instances of model.
    """
    _queryset_class = SoftDeletableQuerySet

    def get_queryset(self):
        """
        Return queryset limited to not deleted entries.
        """
        kwargs = {'model': self.model, 'using': self._db}
        if hasattr(self, '_hints'):
            kwargs['hints'] = self._hints

        return self._queryset_class(**kwargs).filter(is_deleted=False)


class SoftDeletableManager(SoftDeletableManagerMixin, models.Manager):
    pass

# 自定義軟刪除抽象基類
class SoftDeletableModel(models.Model):
    """
    An abstract base class model with a ``is_deleted`` field that
    marks entries that are not going to be used anymore, but are
    kept in db for any reason.
    Default manager returns only not-deleted entries.
    """
    is_deleted = models.BooleanField(default=False)

    class Meta:
        abstract = True  # 成功發(fā)送Signal信號需要將abstract設(shè)置為true
        auto_created = False

    objects = SoftDeletableManager()

    def delete(self, using=None, soft=True, *args, **kwargs):
        """
        Soft delete object (set its ``is_deleted`` field to True).
        Actually delete object if setting ``soft`` to False.
        """
        if soft:
            self.is_deleted = True
            self.save(using=using)
        else:
            return super(SoftDeletableModel, self).delete(using=using, *args, **kwargs)

model demo代碼開發(fā)

class Server(SoftDeletableModel):
    id = models.AutoField(primary_key=True)
    local_ip = models.CharField('內(nèi)網(wǎng)ip', max_length=30, blank=True, null=True)
  
    class Meta:
        db_table = 'dbmanage_server'

class ServerBase(models.Model):
    id = models.AutoField(primary_key=True)
    local_ip = models.CharField('內(nèi)網(wǎng)ip', max_length=30, blank=True, null=True)
    is_deleted = models.BooleanField('是否刪除', default=False)

    class Meta:
        managed = False  # 在migrate時不會創(chuàng)建該表
        db_table = 'dbmanage_server'

繼承了軟刪除模型類SoftDeletableModel的模型server，在進(jìn)行migrate建表操作時推正，自動會給Server表添加上一個is_deleted字段恍涂。后續(xù)的數(shù)據(jù)刪除操作中只需要執(zhí)行delete()，即可將數(shù)據(jù)的is_deleted設(shè)置為True植榕。查詢操作時再沧，不需要加上條件限制，自動會返回is_deleted=False的數(shù)據(jù)尊残。

Tips

1：Server模型無法發(fā)送信號
增加代碼abstract = True（具體細(xì)節(jié)不太了解炒瘸，看源碼里要求的）
2：需要查詢已經(jīng)刪除掉的數(shù)據(jù)
有時候想要展示已經(jīng)刪除的數(shù)據(jù)，但是Server模型里是自動過濾掉刪除數(shù)據(jù)的寝衫。
增加一個ServerBase模型類顷扩，在進(jìn)行查詢時使用該類，記得增加managed=Fasle慰毅，這樣在migrate時不會django不會去創(chuàng)建該表隘截。