Add method to get parent in TreeData (#9701)

server/src/main/java/com/vaadin/data/TreeData.java

@@ -367,6 +367,25 @@ public class TreeData<T> implements Serializable {
                 .unmodifiableList(itemToWrapperMap.get(item).getChildren());
     }
 
+    /**
+     * Get the parent item for the given item.
+     *
+     * @param item
+     *         the item for which to retrieve the parent item for
+     * @return parent item for the given item or {@code null} if the item is a
+     *         root item.
+     * @throws IllegalArgumentException
+     *         if the item does not exist in this structure
+     * @since 8.1.1
+     */
+    public T getParent(T item) {
+        if (!contains(item)) {
+            throw new IllegalArgumentException(
+                    "Item '" + item + "' not in hierarchy");
+        }
+        return itemToWrapperMap.get(item).getParent();
+    }
+
     /**
      * Moves an item to become a child of the given parent item. The new parent
      * item must exist in the hierarchy. Setting the parent to {@code null}

server/src/test/java/com/vaadin/data/provider/TreeDataProviderTest.java

@@ -80,6 +80,14 @@ public class TreeDataProviderTest
         Assert.assertTrue(data.getChildren(null).contains(item));
     }
 
+    @Test
+    public void treeData_get_parent() {
+        StrBean root = rootData.get(0);
+        StrBean firstChild = data.getChildren(root).get(0);
+        Assert.assertNull(data.getParent(root));
+        Assert.assertEquals(root, data.getParent(firstChild));
+    }
+
     @Test
     public void treeData_set_parent() {
         StrBean item1 = rootData.get(0);