如何使用相关对象的自定义管理器？

Question

我有一个自定义管理器。我想用它来处理相关的对象。我在文档中找到了use_for_related_fields。但它不工作，我用它的方式：

class RandomQueryset(models.query.QuerySet): 

    def randomize(self):  
     count = self.count() 
     random_index = random.randint(0, count - 1) 
     return self.all()[random_index] 


class RandomManager(models.Manager): 

    use_for_related_fields = True 

    def get_query_set(self): 
     return RandomQueryset(self.model, using=self._db) 

    def randomize(self): 
     return self.get_query_set().randomize() 

我用了一个模型：

>>> post = PostPages.default_manager.filter(image_gallery__isnull=False).distinct().randomize() 

并试图做同样的M2M相关的对象：

>>> post.image_gallery.randomize() 

出现错误：

AttributeError: 'ManyRelatedManager' object has no attribute 'randomize' 

是有没有可能像我一样使用自定义管理器？如果是这样，你如何使它工作？

编辑

我的模型：

class ShivaImage(models.Model, ImageResizing): 
    image = models.ImageField(upload_to='img') 
    slide_show = models.BooleanField() 
    title = models.CharField(max_length=100) 
    text = models.TextField(max_length=400) 
    ordering = models.IntegerField(blank=True, null=True) 

    objects = RandomManager() 


class PostPages(models.Model): 
    image_gallery = models.ManyToManyField(ShivaImage, blank=True, 
             related_name='gallery',) 
    # all the other fields... 

    objects = RandomManager() 

Answer 1

的管理者设置use_for_related_fields到True将使其可在这一点上到在其上定义了这个经理为默认管理模型的所有关系。这是记录here

class MyManager(models.Manager): 
    use_for_related_fields = True 
    # ... 

我想你只对你PostPages模式启用，不是在你的Gallery模型（或任何模型被称为是通过post_image_gallery参考）。如果您想在此realtion manager上具有其他功能，则需要将use_for_related_fields = True的自定义默认管理器添加到您的Gallery模型中！

Answer 2

关于主题的完整性，Django的1.7（终于）支持using a custom reverse manager，所以你可以做这样的事情（从Django文档只是复制）：

 
from django.db import models 

class Entry(models.Model): 
    objects = models.Manager() # Default Manager 
    entries = EntryManager() # Custom Manager 

b = Blog.objects.get(id=1) 
b.entry_set(manager='entries').all() 

Answer 3

而且，在自定义管理，确保

class EventManager(models.Manager): 

    use_for_related_fields = True 

    def visible_events(self): 
     today = datetime.date.today() 
     # don't do this !!! 
     # unsuitable for related managers as could retrieve extraneous objects 
     # qs = super(EventManager, self).get_query_set() 
     # Use queryset proxy method as follows, instead: 
     qs = self.get_query_set() 
     qs = qs.filter(visible_from__lte=today, visible_to__gte=today) 
     return qs 


class Event(models.Model): 

    visible_from = models.DateField(_(u'visible from'), null=False, blank=False) 
    visible_to = models.DateField(_(u'visible to'), null=False, blank=False) 
    concepts = models.ManyToManyField(Concept, through='ConceptEventRegistration') 

    objects = EventManager() 

使用范例：

通过self.get_query_set访问查询集（） 实现自定义过滤器时，代理方法从相关管理者被称为

my_concept = Concept.objects.get(id=1) 
# retrieve all events related to the object 
my_concept.event_set.all() 
# retrieve all visible events related to the object 
my_concept.event_set.visible_events() 

Answer 4

在Django 2.0 use_for_related_fields是depricated https://docs.djangoproject.com/en/2.0/releases/1.10/#manager-use-for-related-fields-and-inheritance-changes

您应该使用base_manager_namehttps://docs.djangoproject.com/en/2.0/ref/models/options/#django.db.models.Options.base_manager_name

这里有最新的文档https://docs.djangoproject.com/en/2.0/topics/db/managers/#using-managers-for-related-object-access

class MyModel(models.Model): 
    field1 = ... 
    field2 = ... 
    special_manager = MyManager() 

    class Meta: 
     base_manager_name = 'special_manager'