fix UnicastBackendHandler execute error while switching multi-schema.

sharding-proxy/sharding-proxy-backend/src/main/java/org/apache/shardingsphere/shardingproxy/backend/text/admin/UnicastBackendHandler.java

@@ -23,6 +23,7 @@ import org.apache.shardingsphere.shardingproxy.backend.communication.DatabaseCom
 import org.apache.shardingsphere.shardingproxy.backend.communication.jdbc.connection.BackendConnection;
 import org.apache.shardingsphere.shardingproxy.backend.response.BackendResponse;
 import org.apache.shardingsphere.shardingproxy.backend.response.query.QueryData;
+import org.apache.shardingsphere.shardingproxy.backend.schema.LogicSchema;
 import org.apache.shardingsphere.shardingproxy.backend.schema.LogicSchemas;
 import org.apache.shardingsphere.shardingproxy.backend.text.TextProtocolBackendHandler;
 
@@ -46,7 +47,12 @@ public final class UnicastBackendHandler implements TextProtocolBackendHandler {
     
     @Override
     public BackendResponse execute() {
-        databaseCommunicationEngine = databaseCommunicationEngineFactory.newTextProtocolInstance(LogicSchemas.getInstance().getLogicSchemas().values().iterator().next(), sql, backendConnection);
+        LogicSchema logicSchema = backendConnection.getLogicSchema();
+        if (null == logicSchema) {
+            logicSchema = LogicSchemas.getInstance().getLogicSchemas().values().iterator().next();
+            backendConnection.setCurrentSchema(logicSchema.getName());
+        }
+        databaseCommunicationEngine = databaseCommunicationEngineFactory.newTextProtocolInstance(logicSchema, sql, backendConnection);
         return databaseCommunicationEngine.execute();
     }
     

sharding-proxy/sharding-proxy-backend/src/test/java/org/apache/shardingsphere/shardingproxy/backend/text/admin/UnicastBackendHandlerTest.java

@@ -30,6 +30,7 @@ import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.mockito.Mock;
+import org.mockito.Spy;
 import org.mockito.junit.MockitoJUnitRunner;
 
 import java.lang.reflect.Field;
@@ -39,11 +40,13 @@ import static org.junit.Assert.assertThat;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.anyString;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 
 @RunWith(MockitoJUnitRunner.class)
 public final class UnicastBackendHandlerTest {
     
+    @Spy
     private BackendConnection backendConnection = new BackendConnection(TransactionType.LOCAL);
     
     @Mock
@@ -61,6 +64,7 @@ public final class UnicastBackendHandlerTest {
         setDatabaseCommunicationEngine(backendHandler);
         BackendResponse actual = backendHandler.execute();
         assertThat(actual, instanceOf(UpdateResponse.class));
+        verify(backendConnection).setCurrentSchema(null);
         backendHandler.execute();
     }