Fix EntityType creation and deletion in the Django admin

arkindex/documents/admin.py

@@ -157,9 +157,19 @@ class EntityRoleAdmin(admin.ModelAdmin):
 
 
 class EntityTypeAdmin(admin.ModelAdmin):
-    list_display = ('id', 'name', 'color')
+    list_display = ('id', 'corpus', 'name', 'color')
     list_filter = ('corpus', )
-    readonly_fields = ('id', 'corpus', )
+
+    def get_readonly_fields(self, request, obj=None):
+        # Make the corpus field read-only only for existing entity types.
+        # Otherwise, new EntityTypes would be created with corpus=None
+        if obj:
+            return ('id', 'corpus')
+        return ('id', )
+
+    def has_delete_permission(self, request, obj=None):
+        # Require everyone to use the frontend or DestroyEntityType
+        return False
 
 
 admin.site.register(Corpus, CorpusAdmin)