Add global element for default group behaviour.

Add default value 'assign' for default group behaviour which matches group behaviour.
Add logic to IcingaObjectGroups so the class initalizes with the global group behaviour and sets the group operator based on the class operator.
Partial Fix for Icinga#344, Icinga#636, Icinga#824, Icinga#2273

application/forms/SettingsForm.php

@@ -39,6 +39,25 @@ public function setup()
             'value'  => $settings->getStoredValue('default_global_zone')
         ));
 
+        $this->addElement('select', 'default_group_behaviour', array(
+            'label'        => $this->translate('Default group behaviour'),
+            'multiOptions' => $this->eventuallyConfiguredEnum(
+                'default_group_behaviour',
+                array(
+                    'assign' => $this->translate('Assign'),
+                    'add' => $this->translate('Add'),
+                    // Remove (-=) is a group option but global remove isn't useful as all groups would be removed all the time.
+                )
+            ),
+            'description'  => $this->translate(
+                'Icinga Director deploys group objects using the operator assign (=)'
+                . ', which overrides groups set in inherited objects, by default.'
+                . ' This option allows you to adjust the group operator globally to'
+                . ' add (+=) which appends groups from inherited objects.'
+            ),
+            'value'  => $settings->getStoredValue('default_group_behaviour')
+        ));
+
         $this->addElement('text', 'icinga_package_name', array(
             'label'        => $this->translate('Icinga Package Name'),
             'description'  => $this->translate(

library/Director/Objects/IcingaObjectGroups.php

@@ -22,6 +22,8 @@ class IcingaObjectGroups implements Iterator, Countable, IcingaConfigRenderer
 
     protected $object;
 
+    private $operator;
+
     private $position = 0;
 
     protected $idx = array();
@@ -35,6 +37,10 @@ public function __construct(IcingaObject $object)
             $class = $this->getGroupClass();
             $class::prefetchAll($this->object->getConnection());
         }
+
+        // Set the default operator from global config
+        $settings = $this->object->getConnection()->settings();
+        $this->operator($settings->get('default_group_behaviour'));
     }
 
     #[\ReturnTypeWillChange]
@@ -54,6 +60,11 @@ public function hasBeenModified()
         return $this->modified;
     }
 
+    public function operator($val)
+    {
+        $this->operator = $val;
+    }
+
     #[\ReturnTypeWillChange]
     public function current()
     {
@@ -363,7 +374,13 @@ public function toConfigString()
             return '';
         }
 
-        return c::renderKeyValue('groups', c::renderArray($groups));
+        if ($this->operator === "add") {
+            return c::renderKeyOperatorValue('groups', "+=", c::renderArray($groups));
+        } elseif ($this->operator === "remove") {
+            return c::renderKeyOperatorValue('groups', "-=", c::renderArray($groups));
+        } else {	
+            return c::renderKeyValue('groups', c::renderArray($groups));
+	    }
     }
 
     public function toLegacyConfigString($additionalGroups = array())
@@ -376,7 +393,13 @@ public function toLegacyConfigString($additionalGroups = array())
         }
 
         $type = $this->object->getLegacyObjectType();
-        return c1::renderKeyValue($type.'groups', c1::renderArray($groups));
+        if ($this->operator === "add") {
+            return c1::renderKeyOperatorValue('groups', "+=", c1::renderArray($groups));
+        } elseif ($this->operator == "remove") {
+            return c1::renderKeyOperatorValue('groups', "-=", c1::renderArray($groups));
+        } else {	
+            return c1::renderKeyValue($type.'groups', c1::renderArray($groups));
+        }
     }
 
     public function __toString()

library/Director/Settings.php

@@ -12,6 +12,7 @@ class Settings
 
     protected $defaults = [
         'default_global_zone'              => 'director-global',
+        'default_group_behaviour'          => 'assign',
         'icinga_package_name'              => 'director',
         'config_format'                    => 'v2',
         'override_services_varname'        => '_override_servicevars',