Add retriever to CloudObject and allow retrieval of related objects

CloudObjects/SDK/CloudObject.php

@@ -19,7 +19,8 @@ class CloudObject {
 
     private $coid;
     private $node;
-    private $reader;
+    private $reader = null;
+    private $retriever = null;
 
     public function __construct(IRI $coid, Node $node) {
         Assert::eq((string)$coid, $node->getId(), "COID and Node ID must match.");
@@ -45,6 +46,16 @@ class CloudObject {
         return $this->reader;
     }
 
+    /**
+     * Specify an ObjectRetriever to use for retrieval
+     * of related objects.
+     */
+    public function setObjectRetriever(ObjectRetriever $retriever) : self {
+        $this->retriever = $retriever;
+
+        return $this;
+    }
+
     /**
      * Get the COID of this object.
      */
@@ -53,7 +64,7 @@ class CloudObject {
     }
 
     /**
-     * Get the raw object node.
+     * Get the object node encapsulated in this CloudObject.
      */
     public function getObjectNode() : Node {
         return $this->node;
@@ -107,4 +118,19 @@ class CloudObject {
         return $this->getReader()->getFirstValueNode($this->node, $property, $default);
     }
 
+    /**
+     * Get the value of a property and, if it's a COID, retrieve the corresponding CloudObject.
+     */
+    public function getCloudObject($property) : ?CloudObject {
+        Assert::notNull($this->retriever, "No ObjectRetriever set for CloudObject. Cannot retrieve related object.");
+
+        $coid = $this->getReader()->getFirstValueIRI($this->node, $property);
+
+        if (!($coid instanceof IRI)) {
+            return null;
+        }
+
+        return $this->retriever->getCloudObject($coid);
+    }
+
 }