在LIKE语句中插入参数化值

我有一个方法，更新mysql数据库中的记录，查询工作得很好，当简单地使用时，字符串如下:

string query = @"UPDATE Batches SET `State`=@State, `PostDocCount`=@PostDocCount WHERE `FilePath` LIKE '%MYDIRECTORYSTRING%'";

虽然如果我用参数化查询代替MYDIRECTORYSTRING，例如:

string query = @"UPDATE Batches SET `State`=@State, `PostDocCount`=@PostDocCount WHERE `FilePath` LIKE '%@dirName%'";

它不再工作(记录没有更新)-我也确认了@dirName == MYDIRECTORYSTRING。所以我认为这是一个语法问题?(虽然这两个查询似乎都执行ok..)

下面是我的完整方法:

 public void UpdateBatch(string postDocCount, string dirName, string state)
        {
        string query = @"UPDATE Batches SET `State`=@State, `PostDocCount`=@PostDocCount WHERE `FilePath` LIKE '%@dirName%'";
        //Open connection
        if (this.OpenConnection() == true)
        {
            //create mysql command
            MySqlCommand cmd = new MySqlCommand();
            //Assign the query using CommandText
            cmd.CommandText = query;
            //Assign the connection using Connection
            cmd.Connection = connection;
            // Parametized queries 
            cmd.Parameters.AddWithValue("@PostDocCount", postDocCount);
            cmd.Parameters.AddWithValue("@State", state);
            cmd.Parameters.AddWithValue("@dirName", dirName);
            //Execute query
            cmd.ExecuteNonQuery();
            //close connection
            this.CloseConnection();
        }
    }