默认情况下Django 管理员, 丢失更新 or 写倾斜引起的竞争条件可能会发生，因为select_for_update()未使用。 *我的答案 https://stackoverflow.com/questions/27826714/lost-update-vs-write-skew/73847878#73847878解释丢失更新 and 写倾斜.
所以，我用以下代码编写了示例代码select_for_update()阻止丢失更新 or 写倾斜 in Django 管理员如下所示。 *我用了姜戈 3.2.16 and PostgreSQL:
<丢失更新>
例如，您创建store_product table with id, name and stock with models.py如下所示：
store_product table:
| id |
name |
stock |
| 1 |
Apple |
10 |
| 2 |
Orange |
20 |
# "store/models.py"
from django.db import models
class Product(models.Model):
name = models.CharField(max_length=30)
stock = models.IntegerField()
然后，您需要覆盖获取查询集() https://github.com/django/django/blob/main/django/contrib/admin/options.py#L412 with select_for_update() in ProductAdmin():如下所示：
# "store/admin.py"
from django.contrib import admin
from .models import Product
@admin.register(Product)
class ProductAdmin(admin.ModelAdmin):
def get_queryset(self, request):
qs = super().get_queryset(request)
last_part_of_referer = request.META.get('HTTP_REFERER').split('/')[-2]
last_part_of_uri = request.build_absolute_uri().split('/')[-2]
if (last_part_of_referer == "change" and last_part_of_uri == "change"):
qs = qs.select_for_update()
return qs
然后，如果你改变（更新）product如下所示：
SELECT FOR UPDATE and UPDATE queries正在运行交易根据PostgreSQL 查询日志如下所示。 *您可以检查如何记录 PostgreSQL 查询 https://stackoverflow.com/questions/54780698/postgresql-database-log-transaction/73432601#73432601:
而且，如果你不重写get_queryset() in ProductAdmin():如下所示：
# "store/admin.py"
from django.contrib import admin
from .models import Product
@admin.register(Product)
class ProductAdmin(admin.ModelAdmin):
pass
SELECT and UPDATE queries运行如下图所示：
<写入倾斜>
例如，您创建store_doctor table with id, name and on_call with models.py如下所示：
store_doctor table:
| id |
name |
on_call |
| 1 |
John |
True |
| 2 |
Lisa |
True |
# "store/models.py"
from django.db import models
class Doctor(models.Model):
name = models.CharField(max_length=30)
on_call = models.BooleanField()
然后，您需要覆盖响应_更改（） https://docs.djangoproject.com/en/4.1/ref/contrib/admin/#django.contrib.admin.ModelAdmin.response_change with select_for_update() and 保存模型（） https://docs.djangoproject.com/en/4.1/ref/contrib/admin/#django.contrib.admin.ModelAdmin.save_model in DoctorAdmin():如下所示。 *至少一名医生必须待命：
# "store/admin.py"
from django.contrib import admin
from .models import Doctor
from django.db import connection
@admin.register(Doctor)
class DoctorAdmin(admin.ModelAdmin):
def response_change(self, request, obj):
qs = super().get_queryset(request).select_for_update().filter(on_call=True)
obj_length = len(qs)
if obj_length == 0:
obj.on_call = True
obj.save()
return super().response_change(request, obj)
def save_model(self, request, obj, form, change):
last_part_of_path = request.path.split('/')[-2]
if last_part_of_path == "add":
obj.save()
然后，如果你改变（更新）doctor如下所示：
SELECT FOR UPDATE and UPDATE queries正在运行交易但我不知道如何删除the 1st SELECT query浅蓝色如下图：
而且，如果你不重写response_change() and save_model() in DoctorAdmin():如下所示：
# "store/admin.py"
from django.contrib import admin
from .models import Doctor
@admin.register(Doctor)
class DoctorAdmin(admin.ModelAdmin):
pass
SELECT and UPDATE queries运行如下图所示：
例如对于write skew再次，你创造了store_event table with id, name and user with models.py如下所示：
store_event table:
| id |
name |
user |
| 1 |
Make Sushi |
John |
| 2 |
Make Sushi |
Tom |
# "store/models.py"
from django.db import models
class Event(models.Model):
name = models.CharField(max_length=30)
user = models.CharField(max_length=30)
然后，您需要覆盖response_add() with select_for_update() and save_model() in EventAdmin():如下所示。 *只有3位用户可以加入“制作寿司”活动:
# "store/admin.py"
from django.contrib import admin
from .models import Event
from django.db import connection
@admin.register(Event)
class EventAdmin(admin.ModelAdmin):
def response_add(self, request, obj, post_url_continue=None):
qs = super().get_queryset(request).select_for_update() \
.filter(name="Make Sushi")
obj_length = len(qs)
if obj_length < 3:
obj.save()
return super().response_add(request, obj, post_url_continue)
def save_model(self, request, obj, form, change):
last_part_of_path = request.path.split('/')[-2]
if last_part_of_path == "change":
obj.save()
然后，如果你添加event如下所示：
SELECT FOR UPDATE and INSERT queries正在运行交易如下所示：
而且，如果你不重写响应_添加（） https://docs.djangoproject.com/en/4.1/ref/contrib/admin/#django.contrib.admin.ModelAdmin.response_add and save_model() in EventAdmin():如下所示：
# "store/admin.py"
from django.contrib import admin
from .models import Event
@admin.register(Event)
class EventAdmin(admin.ModelAdmin):
pass
Only INSERT query运行如下图所示：
您还可以查看我下面的帖子选择更新在姜戈中：
-
在 Django Admin 中添加数据时如何运行“SELECT FOR UPDATE”而不是“SELECT”？ https://stackoverflow.com/questions/74831244/how-to-run-select-for-update-instead-of-select-when-adding-data-in-django-ad
-
在 Django Admin 中更改和删除数据时，如何运行“SELECT FOR UPDATE”而不是“SELECT”？ https://stackoverflow.com/questions/74807372/how-to-run-select-for-update-instead-of-select-when-changing-and-deleting-da
-
如何在 Django 管理操作中为默认“删除所选”运行“SELECT FOR UPDATE”？ https://stackoverflow.com/questions/74857394/how-to-run-select-for-update-for-the-default-delete-selected-in-django-admin
