findIds: drop no-order requirement, add offset/limit variant

Author: greenrobot

objectbox-java/src/main/java/io/objectbox/query/Query.java

@@ -236,13 +236,20 @@ public List<T> call() {
      */
     @Nonnull
     public long[] findIds() {
-        if (hasOrder) {
-            throw new UnsupportedOperationException("This method is currently only available for unordered queries");
-        }
+        return findIds(0,0);
+    }
+
+    /**
+     * Like {@link #findIds()} but with a offset/limit param, e.g. for pagination.
+     * <p>
+     * Note: a filter set with {@link QueryBuilder#filter} will be silently ignored!
+     */
+    @Nonnull
+    public long[] findIds(final long offset, final long limit) {
         return box.internalCallWithReaderHandle(new CallWithHandle<long[]>() {
             @Override
             public long[] call(long cursorHandle) {
-                return nativeFindIds(handle, cursorHandle, 0, 0);
+                return nativeFindIds(handle, cursorHandle, offset, limit);
             }
         });
     }

tests/objectbox-java-test/src/test/java/io/objectbox/query/QueryTest.java

@@ -458,7 +458,7 @@ public void testRemove() {
     }
 
     @Test
-    public void testFindKeysUnordered() {
+    public void testFindIds() {
         putTestEntitiesScalars();
         assertEquals(10, box.query().build().findIds().length);
 
@@ -470,6 +470,21 @@ public void testFindKeysUnordered() {
         assertEquals(10, keys[2]);
     }
 
+    @Test
+    public void testFindIdsWithOrder() {
+        putTestEntitiesScalars();
+        Query<TestEntity> query = box.query().orderDesc(TestEntity_.simpleInt).build();
+        long[] ids = query.findIds();
+        assertEquals(10, ids.length);
+        assertEquals(10, ids[0]);
+        assertEquals(1, ids[9]);
+
+        ids = query.findIds(3, 2);
+        assertEquals(2, ids.length);
+        assertEquals(7, ids[0]);
+        assertEquals(6, ids[1]);
+    }
+
     @Test
     public void testOr() {
         putTestEntitiesScalars();