Add method for loading relative edges

Summary:
More and more relations are going under edges and I can't work with them from Relatives framework.

This doesn't have the nice transitive property of normal relatives (loading relative objects from relatives loads all of them at once) but I can add it when I need it.

I plan to use it in D3085 (after converting relationships to edges).

Test Plan:
  $task = id(new ManiphestTask())
    ->loadOneWhere('phid = %s', $phid);
  print_r($task->loadRelativeEdges(4));

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D3344

src/infrastructure/storage/lisk/LiskDAO.php

@@ -873,6 +873,10 @@ abstract class LiskDAO {
     return $this;
   }
 
+  final protected function getInSet() {
+    return $this->inSet;
+  }
+
 
 /* -(  Examining Objects  )-------------------------------------------------- */
 

src/infrastructure/storage/lisk/LiskDAOSet.php

@@ -39,9 +39,13 @@
 final class LiskDAOSet {
   private $daos = array();
   private $relatives = array();
+  private $edges = array();
   private $subsets = array();
 
   public function addToSet(LiskDAO $dao) {
+    if ($this->relatives || $this->edges) {
+      throw new Exception("Don't call addToSet() after loading data!");
+    }
     $this->daos[] = $dao;
     $dao->putInSet($this);
     return $this;
@@ -54,6 +58,7 @@ final class LiskDAOSet {
   final public function clearSet() {
     $this->daos = array();
     $this->relatives = array();
+    $this->edges = array();
     foreach ($this->subsets as $set) {
       $set->clearSet();
     }
@@ -99,4 +104,26 @@ final class LiskDAOSet {
     return $relatives;
   }
 
+  public function loadRelativeEdges($type) {
+    $edges = &$this->edges[$type];
+
+    if ($edges === null) {
+      if (!$this->daos) {
+        $edges = array();
+      } else {
+        assert_instances_of($this->daos, 'PhabricatorLiskDAO');
+        $phids = mpull($this->daos, 'getPHID', 'getPHID');
+        $edges = id(new PhabricatorEdgeQuery())
+          ->withSourcePHIDs($phids)
+          ->withEdgeTypes(array($type))
+          ->execute();
+        foreach ($this->daos as $dao) {
+          $dao->attachEdges($edges[$dao->getPHID()]);
+        }
+      }
+    }
+
+    return $edges;
+  }
+
 }

src/infrastructure/storage/lisk/PhabricatorLiskDAO.php

@@ -52,6 +52,18 @@ abstract class PhabricatorLiskDAO extends LiskDAO {
   }
 
 
+  /**
+   * @task edges
+   */
+  public function loadRelativeEdges($type) {
+    if (!$this->getInSet()) {
+      id(new LiskDAOSet())->addToSet($this);
+    }
+    $this->getInSet()->loadRelativeEdges($type);
+    return $this->getEdges($type);
+  }
+
+
   /**
    * @task edges
    */