Fixes #1345 - Workaround for an issue when using mybatis cursor on DB2

src/main/java/org/apache/ibatis/executor/resultset/DefaultResultSetHandler.java

@@ -846,9 +846,11 @@ private String prependPrefix(String columnName, String prefix) {
 
   private void handleRowValuesForNestedResultMap(ResultSetWrapper rsw, ResultMap resultMap, ResultHandler<?> resultHandler, RowBounds rowBounds, ResultMapping parentMapping) throws SQLException {
     final DefaultResultContext<Object> resultContext = new DefaultResultContext<>();
-    skipRows(rsw.getResultSet(), rowBounds);
+    if ( ! rsw.getResultSet().isClosed()) {
+        skipRows(rsw.getResultSet(), rowBounds);
+    }
     Object rowValue = previousRowValue;
-    while (shouldProcessMoreRows(resultContext, rowBounds) && rsw.getResultSet().next()) {
+    while (shouldProcessMoreRows(resultContext, rowBounds) && ! rsw.getResultSet().isClosed() && rsw.getResultSet().next()) {
       final ResultMap discriminatedResultMap = resolveDiscriminatedResultMap(rsw.getResultSet(), resultMap, null);
       final CacheKey rowKey = createRowKey(discriminatedResultMap, rsw, null);
       Object partialObject = nestedResultObjects.get(rowKey);

src/test/java/org/apache/ibatis/executor/resultset/DefaultResultSetHandlerTest.java

@@ -33,6 +33,7 @@
 import java.util.List;
 
 import org.apache.ibatis.builder.StaticSqlSource;
+import org.apache.ibatis.cursor.defaults.DefaultCursor;
 import org.apache.ibatis.executor.Executor;
 import org.apache.ibatis.executor.ExecutorException;
 import org.apache.ibatis.executor.parameter.ParameterHandler;
@@ -42,6 +43,7 @@
 import org.apache.ibatis.mapping.ResultMapping;
 import org.apache.ibatis.mapping.SqlCommandType;
 import org.apache.ibatis.session.Configuration;
+import org.apache.ibatis.session.ResultContext;
 import org.apache.ibatis.session.ResultHandler;
 import org.apache.ibatis.session.RowBounds;
 import org.apache.ibatis.type.TypeHandler;
@@ -65,6 +67,82 @@ public class DefaultResultSetHandlerTest {
   private Connection conn;
   @Mock
   private DatabaseMetaData dbmd;
+
+  /**
+   * Test the behavior of calling {@link DefaultResultSetHandler#handleRowValues}
+   * multiple times with a nested mapping that has ordered results.
+   * This test replicates the behavior of the {@link DefaultCursor}.
+   * 
+   * Some database drivers (like DB2) do not allow any calls to the {@link ResultSet}
+   * after the {@link ResultSet#next()} method has returned false. The Javadoc
+   * mentions that implementations are allowed to throw {@link SQLException} in
+   * this case. In this test we verify that we do not perform any more calls on
+   * the {@link ResultSet} instance after the result set is closed when the end
+   * was reached.
+   */
+  @Test
+  public void shouldNotCallNextWhenResultSetIsClosedForNestedMapping() throws Exception {
+
+    final MappedStatement ms = getNestedAndOrderedMappedStatement();
+    final ResultMap rm = ms.getResultMaps().get(0);
+
+    final Executor executor = null;
+    final ParameterHandler parameterHandler = null;
+    final TestResultHandler resultHandler = new TestResultHandler();
+    final BoundSql boundSql = null;
+    final RowBounds rowBounds = RowBounds.DEFAULT;
+
+    final DefaultResultSetHandler resultSetHandler = new DefaultResultSetHandler(executor, ms, parameterHandler, resultHandler, boundSql, rowBounds);
+
+    when(stmt.getResultSet()).thenReturn(rs);
+    when(rs.getMetaData()).thenReturn(rsmd);
+    when(rs.getType()).thenReturn(ResultSet.TYPE_FORWARD_ONLY);
+    //Simulate a JDBC driver that throws an SQL exception when the end of the result set was reached
+    when(rs.next()).thenReturn(true).thenReturn(false).thenThrow(new SQLException("Not allowed to call next() after false was returned from previous invocation!"));
+    when(rs.getInt("CoLuMn1")).thenReturn(100);
+    when(rs.getInt("CoLuMn2")).thenReturn(200);
+    when(rs.wasNull()).thenReturn(false);
+    when(rsmd.getColumnCount()).thenReturn(2);
+    when(rsmd.getColumnLabel(1)).thenReturn("CoLuMn1");
+    when(rsmd.getColumnType(1)).thenReturn(Types.INTEGER);
+    when(rsmd.getColumnClassName(1)).thenReturn(Integer.class.getCanonicalName());
+    when(rsmd.getColumnLabel(2)).thenReturn("CoLuMn2");
+    when(rsmd.getColumnType(2)).thenReturn(Types.INTEGER);
+    when(rsmd.getColumnClassName(2)).thenReturn(Integer.class.getCanonicalName());
+    when(stmt.getConnection()).thenReturn(conn);
+    when(conn.getMetaData()).thenReturn(dbmd);
+    when(dbmd.supportsMultipleResultSets()).thenReturn(false); // for simplicity.
+
+    final ResultSetWrapper rsw = new ResultSetWrapper(rs, ms.getConfiguration());
+
+    //Read the first and only record
+    resultSetHandler.handleRowValues(rsw, rm, resultHandler, rowBounds, null);
+    assertEquals(1, resultHandler.getResults().size());
+
+    when(rs.isClosed()).thenReturn(true);
+    when(rs.getType()).thenThrow(new SQLException("No interaction allowed when the result set is closed!"));
+
+    //Call handleRowValues a second time like the DefaultCursor does to make sure no more results are present
+    resultSetHandler.handleRowValues(rsw, rm, resultHandler, rowBounds, null);
+    assertEquals(1, resultHandler.getResults().size());
+
+    assertEquals(100, ((HashMap) resultHandler.getResults().get(0)).get("cOlUmN1"));
+    assertEquals(200, ((HashMap) ((HashMap) resultHandler.getResults().get(0)).get("nestedData")).get("cOlUmN2"));
+  }
+
+  private static class TestResultHandler implements ResultHandler<Object> {
+      private final List<Object> results = new ArrayList<>();
+
+        @Override
+        public void handleResult(ResultContext<? extends Object> resultContext) {
+            results.add(resultContext.getResultObject());
+            resultContext.stop();
+        }
+
+        public List<Object> getResults() {
+            return results;
+        }
+  }
 
   /**
    * Contrary to the spec, some drivers require case-sensitive column names when getting result.
@@ -143,5 +221,31 @@ MappedStatement getMappedStatement() {
           }
         }).build();
   }
+
+  MappedStatement getNestedAndOrderedMappedStatement() {
+    final Configuration config = new Configuration();
+    final TypeHandlerRegistry registry = config.getTypeHandlerRegistry();
+
+    ResultMap nestedResultMap = new ResultMap.Builder(config, "nestedTestMap", HashMap.class, new ArrayList<ResultMapping>() {
+      {
+        add(new ResultMapping.Builder(config, "cOlUmN2", "CoLuMn2", registry.getTypeHandler(Integer.class)).build());
+      }
+    }).build();
+    config.addResultMap(nestedResultMap);
+
+    return new MappedStatement.Builder(config, "testSelect", new StaticSqlSource(config, "some select statement"), SqlCommandType.SELECT).resultMaps(
+        new ArrayList<ResultMap>() {
+          {
+            add(new ResultMap.Builder(config, "testMap", HashMap.class, new ArrayList<ResultMapping>() {
+              {
+                add(new ResultMapping.Builder(config, "cOlUmN1", "CoLuMn1", registry.getTypeHandler(Integer.class)).build());
+                add(new ResultMapping.Builder(config, "nestedData").nestedResultMapId("nestedTestMap").build());
+              }
+            }).build());
+          }
+        })
+        .resultOrdered(true)
+        .build();
+  }
 
 }