Allow fields to be excluded from the model_from_serializable_data() p…

…rocess

modelcluster/models.py

@@ -58,8 +58,18 @@ def get_serializable_data_for_fields(model, exclude_fields=None):
     return obj
 
 
-def model_from_serializable_data(model, data, check_fks=True, strict_fks=False):
+def model_from_serializable_data(model, data, check_fks=True, strict_fks=False, exclude_fields=None):
+    """
+    Return an instance of the given model, built from the serialised data
+    (`data`).
+
+    :param check_fks: Optional. If set to False, disables checking of ForeignKey values.
+    :param strict_fks: Optional. If set to True, enables strict foreign key checks.
+    :param exclude_fields: Optional. An iterable of field names to exclude from the process.
+    """
+
     pk_field = model._meta.pk
+    exclude = set(exclude_fields or ())
     kwargs = {}
 
     # If model is a child via multitable inheritance, we need to set ptr_id fields all the way up
@@ -71,6 +81,9 @@ def model_from_serializable_data(model, data, check_fks=True, strict_fks=False):
     kwargs[pk_field.attname] = data['pk']
 
     for field_name, field_value in data.items():
+        if field_name in exclude:
+            continue
+
         try:
             field = model._meta.get_field(field_name)
         except FieldDoesNotExist:
@@ -80,11 +93,11 @@ def model_from_serializable_data(model, data, check_fks=True, strict_fks=False):
         if isinstance(field, ForeignObjectRel):
             continue
 
-        if field.remote_field and isinstance(field.remote_field, models.ManyToManyRel):
+        if field.remote_field and isinstance(field.remote_field, models.ManyToManyRel) and field_name not in exclude:
             related_objects = field.remote_field.model._default_manager.filter(pk__in=field_value)
             kwargs[field.attname] = list(related_objects)
 
-        elif field.remote_field and isinstance(field.remote_field, models.ManyToOneRel):
+        elif field.remote_field and isinstance(field.remote_field, models.ManyToOneRel) and field_name not in exclude:
             if field_value is None:
                 kwargs[field.attname] = None
             else:
@@ -107,6 +120,11 @@ def model_from_serializable_data(model, data, check_fks=True, strict_fks=False):
 
                         else:
                             raise Exception("can't currently handle on_delete types other than CASCADE, SET_NULL and DO_NOTHING")
+        elif field_name in exclude:
+            # In order to not break custom `__init__()` functionality that depends on
+            # field values being available, use Django's DEFERRED mechanism, allowing
+            # the canonical field value to be loaded from the database on access.
+            kwargs[field.name] = models.DEFERRED
         else:
             value = field.to_python(field_value)