Added subsites restriction of asset folders

_config.php

@@ -11,6 +11,7 @@ new SiteTree();
 
 Object::add_extension('LeftAndMain', 'LeftAndMainSubsites');
 Object::add_extension('Group', 'GroupSubsites');
+Object::add_extension('File', 'FileSubsites');
 
 Director::addRules(100, array(
 	'admin/subsites/$Action/$ID/$OtherID' => 'SubsiteAdmin',

code/FileSubsites.php

@@ -0,0 +1,63 @@
+<?php
+
+/**
+ * Extension for the File object to add subsites support
+ */
+class FileSubsites extends DataObjectDecorator {
+	function extraDBFields() {
+		// This is hard-coded to be applied to SiteTree, unfortunately
+        if($this->owner->class == 'File') {
+			return array(
+				'has_one' => array(
+					'Subsite' => 'Subsite',
+				),
+			);
+		}
+	}	
+	
+	/**
+	 * Add subsites-specific fields to the folder editor.
+	 */
+	function updateCMSFields(FieldSet &$fields) {
+		if($this->owner instanceof Folder) {
+			$sites = Subsite::accessible_sites('CMS_ACCESS_AssetAdmin');
+			$fields->addFieldToTab('Root.Details', new DropdownField("SubsiteID", "Subsite", $sites->toDropdownMap('ID', 'Title', "(Public)")));
+		}
+	}
+
+	/**
+	 * Update any requests to limit the results to the current site
+	 */
+	function augmentSQL(SQLQuery &$query) {
+		// If you're querying by ID, ignore the sub-site - this is a bit ugly...
+		if(strpos($query->where[0], ".`ID` = ") === false && strpos($query->where[0], ".ID = ") === false) {
+
+			if($context = DataObject::context_obj()) $subsiteID = (int)$context->SubsiteID;
+			else $subsiteID = (int)Subsite::currentSubsiteID();
+			
+			// The foreach is an ugly way of getting the first key :-)
+			foreach($query->from as $tableName => $info) {
+				$query->where[] = "`$tableName`.SubsiteID IN (0, $subsiteID)";
+				break;
+			}
+
+            $query->orderby = 'SubsiteID' . ($query->orderby ? ', ' : '') . $query->orderby;
+		}
+	}
+	
+	function augmentBeforeWrite() {
+		if(!is_numeric($this->owner->ID) && !$this->owner->SubsiteID) $this->owner->SubsiteID = Subsite::currentSubsiteID();
+	}
+	
+	function alternateCanEdit() {
+		// Check the CMS_ACCESS_SecurityAdmin privileges on the subsite that owns this group
+		$oldSubsiteID = Session::get('SubsiteID');
+
+		Session::set('SubsiteID', $this->owner->SubsiteID);
+		$access = Permission::check('CMS_ACCESS_SecurityAdmin');
+		Session::set('SubsiteID', $oldSubsiteID);
+		
+		return $access;
+	}	
+}
+