Add full support for sets

src/Database.php

@@ -109,7 +109,14 @@ class Database
             if ($newRecord->hasContent() || Configuration::getInstance()->deletedRecords !== 'no') {
                 $oldRecord->setContent($newRecord->getContent(), false);
                 $oldRecord->setLastChanged($newRecord->getLastChanged());
-                // TODO: Add full set support.
+                // Add new sets.
+                foreach (array_diff($newRecord->getSets(), $oldRecord->getSets()) as $newSet) {
+                    $oldRecord->addSet($newSet);
+                }
+                // Remove old sets.
+                foreach (array_diff($oldRecord->getSets(), $newRecord->getSets()) as $oldSet) {
+                    $oldRecord->removeSet($oldSet);
+                }
             } else {
                 $this->entityManager->remove($oldRecord);
             }

src/Entity/Set.php

@@ -209,4 +209,14 @@ class Set extends Entity
             throw $exception;
         }
     }
+
+    /**
+     * Get the set's string representation for comparison.
+     *
+     * @return string The set's unique spec
+     */
+    public function __toString(): string
+    {
+        return $this->getSpec();
+    }
 }