1 files changed, 75 insertions, 7 deletions
diff --git a/server/src/main/java/com/vaadin/data/provider/HierarchicalDataProvider.java b/server/src/main/java/com/vaadin/data/provider/HierarchicalDataProvider.java
index ec54a3a138..8dabdce2cc 100644
--- a/server/src/main/java/com/vaadin/data/provider/HierarchicalDataProvider.java
+++ b/server/src/main/java/com/vaadin/data/provider/HierarchicalDataProvider.java
@@ -15,25 +15,93 @@
  */
 package com.vaadin.data.provider;
 
+import java.util.stream.Stream;
+
 /**
- * 
+ * A common interface for fetching hierarchical data from a data source, such as
+ * an in-memory collection or a backend database.
+ *
  * @author Vaadin Ltd
  * @since 8.1
- * 
+ *
  * @param <T>
+ *            data type
  * @param <F>
+ *            filter type
  */
 public interface HierarchicalDataProvider<T, F> extends DataProvider<T, F> {
 
-    public int getDepth(T item);
+    /**
+     * Get the number of immediate child data items for the parent item returned
+     * by a given query.
+     * 
+     * @param query
+     *            given query to request the count for
+     * @return the count of child data items for the data item
+     *         {@link HierarchicalQuery#getParent()}
+     * 
+     * @throws IllegalArgumentException
+     *             if the query is not of type HierarchicalQuery
+     */
+    @Override
+    public default int size(Query<T, F> query) {
+        if (query instanceof HierarchicalQuery<?, ?>) {
+            return getChildCount((HierarchicalQuery<T, F>) query);
+        }
+        throw new IllegalArgumentException(
+                "Hierarchical data provider doesn't support non-hierarchical queries");
+    }
 
-    public boolean isRoot(T item);
+    /**
+     * Fetches data from this HierarchicalDataProvider using given
+     * {@code query}. Only the immediate children of
+     * {@link HierarchicalQuery#getParent()} will be returned.
+     * 
+     * @param query
+     *            given query to request data with
+     * @return a stream of data objects resulting from the query
+     * 
+     * @throws IllegalArgumentException
+     *             if the query is not of type HierarchicalQuery
+     */
+    @Override
+    public default Stream<T> fetch(Query<T, F> query) {
+        if (query instanceof HierarchicalQuery<?, ?>) {
+            return fetchChildren((HierarchicalQuery<T, F>) query);
+        }
+        throw new IllegalArgumentException(
+                "Hierarchical data provider doesn't support non-hierarchical queries");
+    }
 
-    public T getParent(T item);
+    /**
+     * Get the number of immediate child data items for the parent item returned
+     * by a given query.
+     * 
+     * @param query
+     *            given query to request the count for
+     * @return the count of child data items for the data item
+     *         {@link HierarchicalQuery#getParent()}
+     */
+    public int getChildCount(HierarchicalQuery<T, F> query);
 
-    public boolean isCollapsed(T item);
+    /**
+     * Fetches data from this HierarchicalDataProvider using given
+     * {@code query}. Only the immediate children of
+     * {@link HierarchicalQuery#getParent()} will be returned.
+     * 
+     * @param query
+     *            given query to request data with
+     * @return a stream of data objects resulting from the query
+     */
+    public Stream<T> fetchChildren(HierarchicalQuery<T, F> query);
 
+    /**
+     * Check whether a given item has any children associated with it.
+     * 
+     * @param item
+     *            the item to check for children
+     * @return whether the given item has children
+     */
     public boolean hasChildren(T item);
 
-    public void setCollapsed(T item, boolean b);
 }