SQL-2732: Correct handling of empty select order list (#345) (#346)

Author: bucaojit

src/main/java/com/mongodb/jdbc/MongoResultSetMetaData.java

@@ -100,7 +100,7 @@ public MongoResultSetMetaData(
         columnIndices = new ArrayList<NameSpace>();
         columnInfo = new ArrayList<MongoColumnInfo>();
 
-        if (selectOrder == null) {
+        if (selectOrder == null || selectOrder.isEmpty()) {
             String[] datasources = schema.properties.keySet().toArray(new String[0]);
             Arrays.sort(datasources);
 

src/test/java/com/mongodb/jdbc/MongoResultSetMetaDataTest.java

@@ -21,6 +21,7 @@
 import java.sql.ResultSetMetaData;
 import java.sql.SQLException;
 import java.sql.Types;
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
 import org.bson.BsonValue;
@@ -371,4 +372,21 @@ void testGetDatasource() throws Exception {
         assertThrows(Exception.class, () -> resultSetMetaData.getDatasource(FOO_DUP_COL_LABEL));
         assertThrows(Exception.class, () -> resultSetMetaData.getDatasource(BOT_DUP_COL_LABEL));
     }
+
+    @Test
+    void testEmptySelectOrder() throws SQLException {
+        MongoJsonSchema schema = generateMongoJsonSchema();
+
+        MongoResultSetMetaData nullSelectOrderMetadata =
+                new MongoResultSetMetaData(
+                        schema, null, true, mongoConnection.getLogger(), 0, null);
+
+        List<List<String>> emptySelectOrder = new ArrayList<>();
+        MongoResultSetMetaData emptySelectOrderMetadata =
+                new MongoResultSetMetaData(
+                        schema, emptySelectOrder, true, mongoConnection.getLogger(), 0, null);
+
+        assertEquals(12, nullSelectOrderMetadata.getColumnCount());
+        assertEquals(12, emptySelectOrderMetadata.getColumnCount());
+    }
 }