Django Inlining shows additional fields in the add dialog

Question

I wrote this django 1.7.7 code:

class Color(models.Model):                                                          
    color = models.CharField(max_length=20, primary_key=True)                    
    def __unicode__(self):                                                          
        return str(self.color)                                                      

class Pen(models.Model):                                                            
    label = models.CharField(max_length=20, primary_key=True)                       
    color = models.ForeignKey('Color')

class PenAdmin(admin.ModelAdmin):                                                   
    pass                                                                         

class PenInline(admin.TabularInline):                                               
    model = Pen                                                                     

class ColorAdmin(admin.ModelAdmin):                                                 
    inlines = [PenInline,]                                                          

admin.site.register(Pen, PenAdmin)                                                  
admin.site.register(Color, ColorAdmin)

I want to know why when I click on the add color button in the admin page, it also shows 3 pen fields as in the image below and how to remove them from that specific dialog. I've tried both TabularInline and StackedInline and they look identical.

Answer 1

InlineModelAdmin extra's default value is 3, so you can simply change it extra = 0 in PenInline declaration:

class PenInline(admin.TabularInline):                                               
    model = Pen
    extra = 0

https://docs.djangoproject.com/en/dev/ref/contrib/admin/#django.contrib.admin.InlineModelAdmin.extra

Or look at https://stackoverflow.com/a/2228821/3033586

Or remove ColorAdmin declaration and change last line to admin.site.register(Color)