绕过自定义模型管理器以获取ManyToMany对象

Question

I'm working on a maintenance project which has a model say Business with a custom Model Manager. This custom Model Manager adds some extra filter to all the queries executing on Business models. This Business model has a ManyToMany field to self named Trainers. So far so good, the issue comes in when I try to fetch all the Trainers associated with the Business without applying those filters.

The Business model is as given below:

class Business(Basetable):
    #status P=publish    H=inactive    D=draft    N=new
    name = models.CharField(max_length=120)
    slug = models.SlugField(max_length=150)
    logo=models.OneToOneField("BusinessLogo",null=True,on_delete=models.SET_NULL)
    categories = models.ManyToManyField("BusinessCategory",related_name='allcategories',null=True)
    price_type = models.CharField(max_length=2,
                                      choices=PRICE_CHOICES,
                                      default=YEARLY, null=True, blank=True)
    achievements = models.TextField(null=True, blank=True)
    years_of_experience = models.FloatField(null=True, blank=True)

    trainers = models.ManyToManyField("self",related_name='btrainers',null=True, blank=True, symmetrical=False)
    expense=models.IntegerField(null=True,blank=True)
    objects= CityManager()

    def get_trainers(self):
      return self.trainers.all()

get_trainers is the function which returns all the Trainers associated with the Business, however I want the results to bypass the CityManager and use the default Manager.

Any pointers will be appreciated.

Update:

using use_for_related_fields = False does not work. I found a related bug here. Is there a work around? I know that overriding the default objects is not a good practice, however this is what I have received.

Answer 1

In general, it's better to avoid filtering results in the default Manager :

It's a good idea to be careful in your choice of default manager in order to avoid a situation where overriding get_queryset() results in an inability to retrieve objects you'd like to work with.

But if you can't change the default Manager for backwards-compatibility reasons, you can still explicitly create a plain Manager and get your results using that.

class Business(Basetable):
    ...
    objects = CityManager()  # Still the first listed, and default
    plain_objects = models.Manager()

Now that you have a plain Manager , use it to explicitly access the desired objects:

def get_trainers(self):
    return Business.plain_objects.filter(btrainers__id=self.id)