Use GenericForeignKey

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

@@ -40,14 +40,11 @@ class Migration(migrations.Migration):
                 ),
                 (
                     "model_type",
-                    models.CharField(
+                    models.ForeignKey(
                         blank=True,
-                        default="",
                         help_text="Target model type for this parameter template",
-                        max_length=100,
+                        on_delete=django.db.models.deletion.CASCADE,
-                        validators=[
+                        to="contenttypes.contenttype",
-                            common.validators.validate_parameter_template_model_type
-                        ],
                         verbose_name="Model type",
                     ),
                 ),
@@ -156,13 +153,9 @@ class Migration(migrations.Migration):
                 ),
                 (
                     "model_type",
-                    models.CharField(
+                    models.ForeignKey(
-                        blank=True,
+                        on_delete=django.db.models.deletion.CASCADE,
-                        default="",
+                        to="contenttypes.contenttype",
-                        help_text="Target model type for this parameter",
-                        max_length=100,
-                        validators=[common.validators.validate_parameter_model_type],
-                        verbose_name="Model type",
                     ),
                 ),
                 (
@@ -224,4 +217,10 @@ class Migration(migrations.Migration):
             },
             bases=(InvenTree.models.PluginValidationMixin, models.Model),
         ),
+        migrations.AddIndex(
+            model_name="parameter",
+            index=models.Index(
+                fields=["model_type", "model_id"], name="common_para_model_t_244405_idx"
+            ),
+        ),
     ]

src/backend/InvenTree/common/models.py

@@ -2473,11 +2473,11 @@ class ParameterTemplate(
 
         return [x.strip() for x in self.choices.split(',') if x.strip()]
 
-    model_type = models.CharField(
+    # TODO: Reintroduce validator for model_type
-        max_length=100,
+    model_type = models.ForeignKey(
-        default='',
+        ContentType,
+        on_delete=models.CASCADE,
         blank=True,
-        validators=[common.validators.validate_parameter_template_model_type],
         verbose_name=_('Model type'),
         help_text=_('Target model type for this parameter template'),
     )
@@ -2557,6 +2557,8 @@ class Parameter(
         verbose_name_plural = _('Parameters')
         unique_together = [['model_type', 'model_id', 'template']]
 
+        indexes = [models.Index(fields=['model_type', 'model_id'])]
+
     @staticmethod
     def get_api_url() -> str:
         """Return the API URL associated with the Parameter model."""
@@ -2608,6 +2610,8 @@ class Parameter(
 
         self.calculate_numeric_value()
 
+        # TODO: Check that the model_type for this parameter matches the template
+
         # TODO: Validation of units (check global setting)
 
         # TODO: Validate against plugins
@@ -2652,20 +2656,16 @@ class Parameter(
 
         return model_class.check_related_permission(permission, user)
 
-    model_type = models.CharField(
+    # TODO: Reintroduce validator for model_type
-        max_length=100,
+    model_type = models.ForeignKey(ContentType, on_delete=models.CASCADE)
-        default='',
-        blank=True,
-        validators=[common.validators.validate_parameter_model_type],
-        verbose_name=_('Model type'),
-        help_text=_('Target model type for this parameter'),
-    )
 
     model_id = models.PositiveIntegerField(
         verbose_name=_('Model ID'),
         help_text=_('ID of the target model for this parameter'),
     )
 
+    content_object = GenericForeignKey('model_type', 'model_id')
+
     template = models.ForeignKey(
         ParameterTemplate,
         on_delete=models.CASCADE,