Fix bug in quering with joint labels

hugegraph-core/src/main/java/com/baidu/hugegraph/backend/query/ConditionQuery.java

@@ -21,10 +21,12 @@
 
 import java.util.ArrayList;
 import java.util.Collections;
+import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Iterator;
 import java.util.LinkedHashSet;
 import java.util.List;
+import java.util.Map;
 import java.util.Set;
 
 import com.baidu.hugegraph.backend.BackendException;
@@ -410,6 +412,25 @@ public boolean isFlattened() {
         return true;
     }
 
+    public boolean mayHasDupKeys(Set<HugeKeys> keys) {
+        Map<HugeKeys, Integer> keyCounts = new HashMap<>();
+        for (Condition condition : this.conditions()) {
+            if (!condition.isRelation()) {
+                // Assume may exist duplicate keys when has nested conditions
+                return true;
+            }
+            Relation relation = (Relation) condition;
+            if (keys.contains(relation.key())) {
+                int keyCount = keyCounts.getOrDefault(relation.key(), 0);
+                if (++keyCount > 1) {
+                    return true;
+                }
+                keyCounts.put((HugeKeys) relation.key(), keyCount);
+            }
+        }
+        return false;
+    }
+
     public void optimized(int optimizedType) {
         this.optimizedType = optimizedType;
 

hugegraph-core/src/main/java/com/baidu/hugegraph/backend/query/ConditionQueryFlatten.java

@@ -34,11 +34,16 @@
 import com.baidu.hugegraph.util.InsertionOrderUtil;
 import com.baidu.hugegraph.util.NumericUtil;
 import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableSet;
 
 public final class ConditionQueryFlatten {
 
+    private static final Set<HugeKeys> SPECIAL_KEYS = ImmutableSet.of(
+            HugeKeys.LABEL
+    );
+
     public static List<ConditionQuery> flatten(ConditionQuery query) {
-        if (query.isFlattened()) {
+        if (query.isFlattened() && !query.mayHasDupKeys(SPECIAL_KEYS)) {
             return Arrays.asList(query);
         }
 

hugegraph-test/src/main/java/com/baidu/hugegraph/core/VertexCoreTest.java

@@ -4042,6 +4042,56 @@ public void testQueryVerticesByLabelsWithOneLabelNotExist() {
         });
     }
 
+    @Test
+    public void testQueryByJointLabels() {
+        HugeGraph graph = graph();
+        init5Persons();
+        init5Computers();
+        init10Vertices();
+
+        GraphTraversalSource g = graph.traversal();
+
+        List<Vertex> vertices = g.V().hasLabel("person").hasLabel("computer")
+                                 .toList();
+        Assert.assertEquals(0, vertices.size());
+
+        vertices = g.V().hasLabel("person").hasLabel("person")
+                    .toList();
+        Assert.assertEquals(5, vertices.size());
+
+        vertices = g.V().hasLabel("person", "computer").hasLabel("person")
+                    .toList();
+        Assert.assertEquals(5, vertices.size());
+        for (Vertex vertex : vertices) {
+            Assert.assertEquals("person", vertex.label());
+        }
+
+        vertices = g.V().hasLabel("person", "computer").hasLabel("computer")
+                    .toList();
+        Assert.assertEquals(5, vertices.size());
+        for (Vertex vertex : vertices) {
+            Assert.assertEquals("computer", vertex.label());
+        }
+
+        vertices = g.V().hasLabel("person").hasLabel("person", "computer")
+                    .toList();
+        Assert.assertEquals(5, vertices.size());
+        for (Vertex vertex : vertices) {
+            Assert.assertEquals("person", vertex.label());
+        }
+
+        vertices = g.V().hasLabel("person", "computer")
+                    .hasLabel("person", "author").toList();
+        Assert.assertEquals(5, vertices.size());
+        for (Vertex vertex : vertices) {
+            Assert.assertEquals("person", vertex.label());
+        }
+
+        vertices = g.V().hasLabel("person", "computer")
+                    .hasLabel("book", "language").toList();
+        Assert.assertEquals(0, vertices.size());
+    }
+
     private void init10Vertices() {
         HugeGraph graph = graph();