Empty form for inlines breaks when using db_default on primary key field

[Mariusz Felisiak]

Using db_default with the new UUID4 or UUID7 functions breaks saving inlines. For example,

• models.py

  class MyMain(models.Model):
      uuid = models.UUIDField(primary_key=True, db_default=UUID7(), editable=False, verbose_name="UUID")
      name = models.CharField(max_length=100)
  
  class MyChild(models.Model):
      name = models.CharField(max_length=100)
      parent = models.ForeignKey(MyMain, models.DB_CASCADE)
  

• admin.py

class ChildAdmin(admin.TabularInline):
    model = MyChild
    extra = 0


class MainAdmin(admin.ModelAdmin):
    inlines = [ChildAdmin]


admin.site.register(MyChild)
admin.site.register(MyMain, MainAdmin)

DatabaseDefault instances are rendered as values of the parent fields:

<tr class="form-row  empty-form" id="mychild_set-empty">
  <td class="original">      
     <input type="hidden" name="mychild_set-__prefix__-id" id="id_mychild_set-__prefix__-id">
     <input type="hidden" name="mychild_set-__prefix__-parent" value="&lt;django.db.models.expressions.DatabaseDefault object at 0x750a2aa14ad0&gt;" id="id_mychild_set-__prefix__-parent">
  </td>
  ...

which causes the following error when trying to save:

[{'parent': ['The inline value did not match the parent instance.']}]

[Mariusz Felisiak]

The following fixes this issue for me:

django/forms/widgets.py

@@ -343 +343 @@
         """
         Return a value as it should appear when rendered in a template.
         """
-        if value == "" or value is None:
+        from django.db.models.expressions import DatabaseDefault
+
+        if value == "" or value is None or isinstance(value, DatabaseDefault):
             return None
         if self.is_localized:
             return formats.localize_input(value)