Question

I’m experiencing this error in Django 1.2 admin.

Scenario:

I have two applications, say app1 and app2 inside my project.
In both of these apps, I defined their respective admin.py files to hook each apps respective models to django’s admin site.

Inside app1 admin.py, I defined three ModelAdmin classes corresponding to three models class in app1 and registered two of them to the admin site.

class App11stModelAdmin (admin.ModelAdmin):
    #class definitions here

    #This class is an abstract class
    #class Meta:
    #   abstract = True

class App12ndModelAdmin (admin.ModelAdmin):
    #class definitions here

class App13rdModelAdmin (admin.ModelAdmin):
    #class definitions here

#register to admin site two of them
admin.site.register(App12ndModel, App12ndModelAdmin)
admin.site.register(App13rdModel, App13rdModelAdmin)

Inside app2, I imported app1.App11stModelAdmin to define the admin model of an app2 model.

inside admin.py of app2:

from app1.admin import App11stModelAdmin

class App21stModelAdmin(App11stModelAdmin):
    #define some things here

#register App21stModelAdmin to admin site
admin.site.register(App21stModel, App21stModelAdmin)

With this code, I am getting this error message:

AlreadyRegistered at /admin/

The model App12ndModel is already registered

Request Method:     GET
Request URL:    http://127.0.0.1:8000/admin/
Django Version:     1.2
Exception Type:     AlreadyRegistered
Exception Value:    

The model App12ndModel is already registered

This strange because I’m sure I’m only registering that model’s admin once. When I commented out the register statement for that model, I got the same error, but now for App13rdModel model.

In the meantime, to fix this issue, I removed the registration statements and instead put them inside a ‘static’ function inside app1 admin.py.

like:
inside app1 admin.py

def register():
    admin.site.register(App12ndModel, App12ndModelAdmin)
    admin.site.register(App13rdModel, App13rdModelAdmin)

and then in app2 admin.py

I included the register function in the import:

from app1.model import App11stModelAdmin, register

 ......
 ......
#register the two admin model in app1 inside app2 admin.py by calling the register function
register()

And this works. I am not getting the Already Registered error anymore.

Question:

What did I do which resulted to that error? I am new to Django and Python.

Thank you very much!

Answer 1

admin.py files are executed by Django during runtime so if you import an admin.py script into another script, you are actually executing the exposed admin.site.register functions again, which thus gives you the Already Registered error.

This is in fact standard Python behavior. Consider the following script (save as sample.py):

def multiplier(x,y):
    return x*y

def sample_write(text):
    out = open("out.txt","w")
    out.write(text)
    out.close()

sample_write("hey") # Notice this executed function

When you open your Python interpreter in the same directory and do import sample it will write the out.txt output. The same case when you selectively import the multiplier function like from sample import multiplier, the output file is still written. The only way to avoid the output file being written is to comment out the executed function in the script or wrap it into another function.