Django.contrib.contenttypes.models中ContentType的get_for_model_unoptimised方法详解

The get_for_model_unoptimised method in django.contrib.contenttypes.models is a method that retrieves the ContentType object for a given Django model class. This method is an unoptimized version of get_for_model method and is only meant to be used in very specific, low-level scenarios where performance is not a concern.

Here is a detailed explanation of the get_for_model_unoptimised method, along with an example of how it can be used:

The get_for_model_unoptimised method takes a model class as its argument and returns the corresponding ContentType object. The ContentType object represents a model class and is used to track all models across different applications in a Django project.

Here is the signature of the get_for_model_unoptimised method:

def get_for_model_unoptimised(model: Type[Model]) -> ContentType:
    ...

The method first checks if the given model class already has a cached ContentType object. If it does, the cached object is returned. Otherwise, it performs a lookup in the ContentType model table to find the ContentType object for the given model class.

Here is an example that demonstrates how to use the get_for_model_unoptimised method:

from django.contrib.contenttypes.models import ContentType
from myapp.models import MyModel

# Get the ContentType object for the MyModel class
content_type = ContentType.get_for_model_unoptimised(MyModel)

# Access attributes of the ContentType object
print(content_type.id)  # The ID of the ContentType object
print(content_type.app_label)  # The app label of the model
print(content_type.model)  # The model name

# Get all objects of the MyModel class
my_model_objects = content_type.model_class().objects.all()
for obj in my_model_objects:
    print(obj)

In this example, we import the ContentType class from django.contrib.contenttypes.models and the MyModel class from myapp.models. We then call the get_for_model_unoptimised method, passing the MyModel class as the argument, to retrieve the corresponding ContentType object.

We can then access various attributes of the ContentType object, such as its ID, app label, and model name. We can also use the model_class method of the ContentType object to access the model class itself and perform operations on it. In this example, we retrieve all objects of the MyModel class using the model_class method and print them out.

It is important to note that the get_for_model_unoptimised method should be used with caution and only in scenarios where performance is not a concern. In most cases, it is recommended to use the get_for_model method, which is optimized for performance and has additional caching mechanisms.