修复判断事务时Db实例错误 (#532)

src/Db/Query/Query.php

@@ -184,6 +184,11 @@ abstract class Query implements IQuery
      */
     public function getDb(): IDb
     {
+        if (!$this->isInitDb)
+        {
+            $this->db = Db::getInstance($this->poolName, $this->queryType);
+        }
+
         return $this->db;
     }
 
@@ -886,15 +891,7 @@ abstract class Query implements IQuery
     {
         try
         {
-            $db = &$this->db;
-            if (!$this->isInitDb)
-            {
-                $db = Db::getInstance($this->poolName, $this->queryType);
-            }
-            if (!$db)
-            {
-                return new $resultClass(false);
-            }
+            $db = $this->getDb();
             $stmt = $db->prepare($sql);
             $binds = $this->binds;
             $this->binds = [];
@@ -971,7 +968,12 @@ abstract class Query implements IQuery
      */
     protected function isInTransaction(): bool
     {
-        return QueryType::WRITE === $this->queryType && Db::getInstance($this->poolName)->inTransaction();
+        if (QueryType::WRITE !== $this->queryType)
+        {
+            return false;
+        }
+
+        return $this->getDb()->inTransaction();
     }
 
     /**