[feature] Add field list_handling to AbstractTemplate model

openwisp_controller/config/admin.py

@@ -831,6 +831,7 @@ class TemplateAdmin(MultitenantAdminMixin, BaseConfigAdmin, SystemDefinedVariabl
         'name',
         'organization',
         'type',
+        'list_handling',
         'backend',
         'vpn',
         'auto_cert',

openwisp_controller/config/base/base.py

@@ -155,10 +155,13 @@ def get_backend_instance(self, template_instances=None, context=None, **kwargs):
             if template_instances is None:
                 template_instances = self.templates.all()
             templates_list = list()
+            templates_list_handling = list()
             for t in template_instances:
                 templates_list.append(t.config)
+                templates_list_handling.append(t.list_handling)
                 context.update(t.get_context())
             kwargs['templates'] = templates_list
+            kwargs['templates_list_handling'] = templates_list_handling
         # pass context to backend if get_context method is defined
         if hasattr(self, 'get_context'):
             context.update(self.get_context())

openwisp_controller/config/base/template.py

@@ -15,6 +15,11 @@
 from .base import BaseConfig
 
 TYPE_CHOICES = (('generic', _('Generic')), ('vpn', _('VPN-client')))
+LIST_HANDLING_CHOICES = (
+    ('insert_at_beginning', _('Insert items at the beginning')),
+    ('append_at_end', _('Append items at the end')),
+    ('override', _('Override all items')),
+)
 
 
 def default_auto_cert():
@@ -55,6 +60,18 @@ class AbstractTemplate(ShareableOrgMixinUniqueName, BaseConfig):
         db_index=True,
         help_text=_('template type, determines which features are available'),
     )
+    list_handling = models.CharField(
+        _('list handling'),
+        max_length=20,
+        choices=LIST_HANDLING_CHOICES,
+        default='append_at_end',
+        db_index=True,
+        help_text=_(
+            'list handling, determines how list items in this template'
+            ' are handled if the same list exists in a previously '
+            'applied template'
+        ),
+    )
     default = models.BooleanField(
         _('enabled by default'),
         default=False,

openwisp_controller/config/migrations/0054_template_list_handling.py

@@ -0,0 +1,31 @@
+# Generated by Django 4.2.7 on 2023-11-09 18:01
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("config", "0053_vpnclient_secret"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="template",
+            name="list_handling",
+            field=models.CharField(
+                choices=[
+                    ("insert_at_beginning", "Insert items at the beginning"),
+                    ("append_at_end", "Append items at the end"),
+                    ("override", "Override all items"),
+                ],
+                db_index=True,
+                default="append_at_end",
+                help_text="list handling, determines how list items in this "
+                "template are handled if the same list exists in a previously"
+                " applied template",
+                max_length=20,
+                verbose_name="list handling",
+            ),
+        ),
+    ]