如何使用相關對象的自定義管理器？

Question

我有一個自定義管理器。我想用它來處理相關的對象。我在文檔中找到了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() 

我用了一個模型：

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

並試圖做同樣的M2M相關的對象：

>>> post.image_gallery.randomize() 

出現錯誤：

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

是有沒有可能像我一樣使用自定義管理器？如果是這樣，你如何使它工作？

編輯

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

的管理者設置use_for_related_fields到True將使其可在這一點上到在其上定義了這個經理爲默認管理模型的所有關係。這是記錄here

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

我想你只對你PostPages模式啓用，不是在你的Gallery模型（或任何模型被稱爲是通過post_image_gallery參考）。如果您想在此realtion manager上具有其他功能，則需要將use_for_related_fields = True的自定義默認管理器添加到您的Gallery模型中！

Answer 2

關於主題的完整性，Django的1.7（終於）支持using a custom reverse manager，所以你可以做這樣的事情（從Django文檔只是複製）：

 
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，在自定義管理，確保

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() 

使用範例：

通過self.get_query_set訪問查詢集（） 實現自定義過濾器時，代理方法從相關管理者被稱爲

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

您應該使用base_manager_namehttps://docs.djangoproject.com/en/2.0/ref/models/options/#django.db.models.Options.base_manager_name

這裏有最新的文檔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'