Closes #97: Introduce the exempt_models config parameter (#109)

* Closes #97: Introduce the exempt_models config parameter to disable branching support for specific plugin models

* Add warning

Author: jeremystretch

docs/configuration.md

@@ -1,5 +1,33 @@
 # Configuration Parameters
 
+## `exempt_models`
+
+Default: `[]` (empty list)
+
+A list of models provided by other plugins which should be exempt from branching support. (Only models which support change logging need be listed; all other models are ineligible for branching support.)
+
+!!! warning
+    A model may not be exempted from branching support if it has one or more relationships to models for which branching is supported. Branching **must** be supported consistently for all inter-related models; otherwise, data corruption can occur. Configure this setting only if you have a specific need to disable branching for certain models provided by plugins.
+
+Models must be specified by app label and model name, as such:
+
+```python
+exempt_models = (
+    'my_plugin.foo',
+    'my_plugin.bar',
+)
+```
+
+It is also possible to exclude _all_ models from within a plugin by substituting an asterisk (`*`) for the model name:
+
+```python
+exempt_models = (
+    'my_plugin.*',
+)
+```
+
+---
+
 ## `max_working_branches`
 
 Default: None

netbox_branching/__init__.py

@@ -1,7 +1,7 @@
 from django.conf import settings
 from django.core.exceptions import ImproperlyConfigured
 
-from netbox.plugins import PluginConfig
+from netbox.plugins import PluginConfig, get_plugin_config
 from netbox.registry import registry
 
 
@@ -22,6 +22,9 @@ class AppConfig(PluginConfig):
         # The maximum number of branches which can be provisioned simultaneously
         'max_branches': None,
 
+        # Models from other plugins which should be excluded from branching support
+        'exempt_models': [],
+
         # This string is prefixed to the name of each new branch schema during provisioning
         'schema_prefix': 'branch_',
     }
@@ -42,11 +45,20 @@ def ready(self):
             )
 
         # Record all object types which support branching in the NetBox registry
-        if 'branching' not in registry['model_features']:
-            registry['model_features']['branching'] = {
-                k: v for k, v in registry['model_features']['change_logging'].items()
-                if k not in constants.EXCLUDED_APPS
-            }
+        exempt_models = (
+            *constants.EXEMPT_MODELS,
+            *get_plugin_config('netbox_branching', 'exempt_models'),
+        )
+        branching_models = {}
+        for app_label, models in registry['model_features']['change_logging'].items():
+            # Wildcard exclusion for all models in this app
+            if f'{app_label}.*' in exempt_models:
+                continue
+            branching_models[app_label] = [
+                model for model in models
+                if f'{app_label}.{model}' not in exempt_models
+            ]
+        registry['model_features']['branching'] = branching_models
 
 
 config = AppConfig

netbox_branching/constants.py

@@ -10,8 +10,8 @@
 # URL query parameter name
 QUERY_PARAM = '_branch'
 
-# Apps which are explicitly excluded from branching
-EXCLUDED_APPS = (
-    'netbox_branching',
-    'netbox_changes',
+# Models for which branching support is explicitly disabled
+EXEMPT_MODELS = (
+    'netbox_branching.*',
+    'netbox_changes.*',
 )