Add validator for ParameterTemplate model type

- Update migrations
- Make Parameter class abstract (for now)
- Validators

src/backend/InvenTree/common/migrations/0040_parametertemplate.py

@@ -1,5 +1,6 @@
 # Generated by Django 4.2.25 on 2025-10-28 11:11
 
+import common.validators
 import InvenTree.models
 import InvenTree.validators
 from django.db import migrations, models
@@ -62,6 +63,17 @@ class Migration(migrations.Migration):
                         verbose_name="Description",
                     ),
                 ),
+                (
+                    "model_type",
+                    models.CharField(
+                        blank=True,
+                        default="",
+                        help_text="Target model type for this parameter",
+                        max_length=100,
+                        validators=[common.validators.validate_parameter_template_model_type],
+                        verbose_name="Model type",
+                    ),
+                ),
                 (
                     "checkbox",
                     models.BooleanField(

src/backend/InvenTree/common/migrations/0041_auto_20251028_1112.py

@@ -8,6 +8,11 @@ def copy_templates(old_model, new_model):
     
     templates = []
 
+    # Clear out all existing instances
+    new_model.objects.all().delete()
+
+    assert new_model.objects.count() == 0
+
     for template in old_model.objects.all():
         templates.append(new_model(
             name=template.name,
@@ -23,6 +28,8 @@ def copy_templates(old_model, new_model):
         new_model.objects.bulk_create(templates)
         print(f"Migrated {len(templates)} ParameterTemplate instances.")
 
+    assert new_model.objects.count() == len(templates)
+
 
 def forward_copy_templates(apps, schema_editor):
     """Forward migration: copy from PartParameterTemplate to ParameterTemplate."""
@@ -43,6 +50,7 @@ def reverse_copy_templates(apps, schema_editor):
 class Migration(migrations.Migration):
 
     dependencies = [
+        ("part", "0132_partparametertemplate_selectionlist"),
         ("common", "0040_parametertemplate"),
     ]
 

src/backend/InvenTree/common/models.py

@@ -72,14 +72,21 @@ class RenderMeta(enums.ChoicesMeta):
     """Metaclass for rendering choices."""
 
     choice_fnc = None
+    allow_blank: bool = False
+    blank_label: str = '------'
 
     @property
     def choices(self):
         """Return a list of choices for the enum class."""
         fnc = getattr(self, 'choice_fnc', None)
         if fnc:
-            return fnc()
-        return []
+            options = fnc()
+        options = []
+
+        if self.allow_blank:
+            options.insert(0, ('', self.blank_label))
+
+        return options
 
 
 class RenderChoices(models.TextChoices, metaclass=RenderMeta):  # type: ignore
@@ -2385,6 +2392,12 @@ class ParameterTemplate(
     class Meta:
         """Metaclass options for the ParameterTemplate model."""
 
+    class ModelChoices(RenderChoices):
+        """Model choices for parameter templates."""
+
+        allow_blank = True
+        choice_fnc = common.validators.parameter_model_options
+
     @staticmethod
     def get_api_url() -> str:
         """Return the API URL associated with the ParameterTemplate model."""
@@ -2467,6 +2480,15 @@ class ParameterTemplate(
 
         return [x.strip() for x in self.choices.split(',') if x.strip()]
 
+    model_type = models.CharField(
+        max_length=100,
+        default='',
+        blank=True,
+        validators=[common.validators.validate_parameter_template_model_type],
+        verbose_name=_('Model type'),
+        help_text=_('Target model type for this parameter'),
+    )
+
     name = models.CharField(
         max_length=100,
         verbose_name=_('Name'),
@@ -2532,6 +2554,9 @@ class Parameter(
     class Meta:
         """Meta options for Parameter model."""
 
+        # TODO: Make this non-abstract, actually implement...
+        abstract = True
+
         verbose_name = _('Parameter')
         verbose_name_plural = _('Parameters')
         unique_together = [['model_type', 'model_id', 'template']]

src/backend/InvenTree/common/serializers.py

@@ -711,11 +711,31 @@ class ParameterTemplateSerializer(
             'name',
             'units',
             'description',
+            'model_type',
             'checkbox',
             'choices',
             'selectionlist',
         ]
 
+    def __init__(self, *args, **kwargs):
+        """Override the model_type field to provide dynamic choices."""
+        super().__init__(*args, **kwargs)
+
+        if len(self.fields['model_type'].choices) == 0:
+            self.fields[
+                'model_type'
+            ].choices = common.validators.attachment_model_options()
+
+    # Note: The choices are overridden at run-time on class initialization
+    model_type = serializers.ChoiceField(
+        label=_('Model Type'),
+        default='',
+        choices=common.validators.attachment_model_options(),
+        required=False,
+        allow_blank=True,
+        allow_null=True,
+    )
+
 
 class IconSerializer(serializers.Serializer):
     """Serializer for an icon."""

src/backend/InvenTree/common/validators.py

@@ -10,6 +10,47 @@ import common.icons
 from common.settings import get_global_setting
 
 
+def parameter_model_types():
+    """Return a list of valid parameter model choices."""
+    import InvenTree.models
+
+    return list(
+        InvenTree.helpers_model.getModelsWithMixin(
+            InvenTree.models.InvenTreeParameterMixin
+        )
+    )
+
+
+def parameter_model_options():
+    """Return a list of options for models which support parameters."""
+    return [
+        (model.__name__.lower(), model._meta.verbose_name)
+        for model in parameter_model_types()
+    ]
+
+
+def validate_parameter_model_type(value: str):
+    """Ensure that the provided parameter model is valid."""
+    model_names = [el[0] for el in parameter_model_options()]
+    if value not in model_names:
+        raise ValidationError('Model type does not support parameters')
+
+
+def validate_parameter_template_model_type(value: str):
+    """Ensure that the provided model type is valid.
+
+    Note: A ParameterTemplate may have a blank model type.
+    """
+    value = str(value).strip()
+
+    if not value:
+        # Empty values are allowed
+        return
+
+    # Pass any other value to the Parameter model type validator
+    validate_parameter_model_type(value)
+
+
 def attachment_model_types():
     """Return a list of valid attachment model choices."""
     import InvenTree.models