From 6c76b309bfa8e56a63bd5596eaae43bc66ae2d00 Mon Sep 17 00:00:00 2001
From: Oliver Walters <oliver.henry.walters@gmail.com>
Date: Mon, 24 Nov 2025 13:14:36 +0000
Subject: [PATCH] Add custom serializer field for ContentType with choices

---
 .../InvenTree/InvenTree/helpers_model.py      | 19 ++++++
 .../InvenTree/InvenTree/serializers.py        | 65 +++++++++++++++++++
 2 files changed, 84 insertions(+)

diff --git a/src/backend/InvenTree/InvenTree/helpers_model.py b/src/backend/InvenTree/InvenTree/helpers_model.py
index 16338266d8..9e0e207e21 100644
--- a/src/backend/InvenTree/InvenTree/helpers_model.py
+++ b/src/backend/InvenTree/InvenTree/helpers_model.py
@@ -281,6 +281,25 @@ def getModelsWithMixin(mixin_class) -> list:
     return [x for x in db_models if x is not None and issubclass(x, mixin_class)]
 
 
+def getModelChoicesWithMixin(
+    mixin_class, allow_null: bool = False
+) -> list[tuple[str, str]]:
+    """Return a list of model choices (app_label.model_name, verbose_name) for models that inherit from the given mixin class."""
+    choices = []
+
+    if allow_null:
+        choices.append((None, _('None')))
+
+    models = getModelsWithMixin(mixin_class)
+
+    for model in models:
+        label = f'{model._meta.app_label}.{model._meta.model_name}'
+        name = model._meta.verbose_name
+        choices.append((label, name))
+
+    return choices
+
+
 def notify_responsible(
     instance,
     sender,
diff --git a/src/backend/InvenTree/InvenTree/serializers.py b/src/backend/InvenTree/InvenTree/serializers.py
index dd1e096de7..82d336127c 100644
--- a/src/backend/InvenTree/InvenTree/serializers.py
+++ b/src/backend/InvenTree/InvenTree/serializers.py
@@ -28,6 +28,7 @@ import InvenTree.ready
 from common.currency import currency_code_default, currency_code_mappings
 from InvenTree.fields import InvenTreeRestURLField, InvenTreeURLField
 from InvenTree.helpers import str2bool
+from InvenTree.helpers_model import getModelChoicesWithMixin
 
 from .setting.storages import StorageBackends
 
@@ -716,3 +717,67 @@ class RemoteImageMixin(metaclass=serializers.SerializerMetaclass):
             raise ValidationError(_('Failed to download image from remote URL'))
 
         return url
+
+
+class ContentTypeField(serializers.Field):
+    """Serializer field which represents a ContentType as 'app_label.model_name'.
+
+    This field converts a ContentType instance to a string representation in the format 'app_label.model_name' during serialization, and vice versa during deserialization.
+
+    Additionally, a "mixin_class" can be supplied to the field, which will restrict the valid content types to only those models which inherit from the specified mixin.
+    """
+
+    mixin_class = None
+
+    def __init__(self, *args, mixin_class=None, **kwargs):
+        """Initialize the ContentTypeField.
+
+        Args:
+            mixin_class: Optional mixin class to restrict valid content types.
+        """
+        self.mixin_class = mixin_class
+        super().__init__(*args, **kwargs)
+
+        # Override the 'choices' field, to limit to the appropriate models
+        if self.mixin_class is not None:
+            self.choices = getModelChoicesWithMixin(
+                self.mixin_class, allow_null=kwargs.get('allow_null', False)
+            )
+
+    def to_representation(self, value):
+        """Convert ContentType instance to string representation."""
+        return f'{value.app_label}.{value.model}'
+
+    def to_internal_value(self, data):
+        """Convert string representation back to ContentType instance."""
+        from django.contrib.contenttypes.models import ContentType
+
+        content_type = None
+
+        try:
+            app_label, model = data.split('.')
+            content_types = ContentType.objects.filter(app_label=app_label, model=model)
+
+            if content_types.exists() and content_types.count() == 1:
+                # Try exact match first
+                content_type = content_types.first()
+            else:
+                # Try lookup just on model name
+                content_types = ContentType.objects.filter(model=model)
+                if content_types.exists() and content_types.count() == 1:
+                    content_type = content_types.first()
+
+        except Exception:
+            raise ValidationError(_('Invalid content type format'))
+
+        if content_type is None:
+            raise ValidationError(_('Content type not found'))
+
+        if self.mixin_class is not None:
+            model_class = content_type.model_class()
+            if not issubclass(model_class, self.mixin_class):
+                raise ValidationError(
+                    _('Content type does not match required mixin class')
+                )
+
+        return content_type