在 ODP.NET 中选择最近使用 ALTER TABLE 插入的列时出错

Question

1- 使用 Oracle.DataAccess 连接到 Oracle XE

2-执行命令向表中添加列：alter table TABLE add COLUMN b int;

3- 执行命令选择该列

4- 使用 DataReader 读取。应用程序引发 IndexOutOfRangeException：无法在结果集中找到指定的列

5- 重启应用，查询正常运行

为什么DataReader无法访问我刚才创建的列？

这是一个大而简单的测试代码：

private void button1_Click(object sender, EventArgs e)
{
    using (OracleConnection con = new OracleConnection(Settings.Default.CS))
    {
        con.Open();
        try
        {
            using (OracleCommand com = new OracleCommand())
            {
                com.Connection = con;

                // Create a test table
                com.CommandText = "CREATE TABLE Test (a int)";
                com.ExecuteNonQuery();

                // Add one column
                com.CommandText = "ALTER TABLE Test ADD b int";
                com.ExecuteNonQuery();

                com.CommandText = "SELECT * FROM Test";
                using (DbDataReader dr = com.ExecuteReader())
                {
                    MessageBox.Show(dr.FieldCount.ToString());
                    // Here is showing "2", thats ok
                }
            }
        }
        finally
        {
            con.Close();
        }
    }
}

private void button2_Click(object sender, EventArgs e)
{
    using (OracleConnection con = new OracleConnection(Settings.Default.CS))
    {
        con.Open();
        try
        {
            using (OracleCommand com = new OracleCommand())
            {
                OracleTransaction trans = con.BeginTransaction();
                try
                {
                    // Add a column to table already created
                    com.Connection = con;
                    com.CommandText = "ALTER TABLE Test ADD c int";
                    com.ExecuteNonQuery();

                    // Insert a value, ok
                    com.CommandText = "INSERT INTO TEST (a, b, c) VALUES (1, 2, 3)";
                    com.ExecuteNonQuery();

                    trans.Commit();
                }
                catch
                {
                    trans.Rollback();
                    throw;
                }

                // Selecting only "c" column
                com.CommandText = "SELECT c FROM Test";
                using (DbDataReader dr = com.ExecuteReader())
                {
                    if (dr.Read())
                        MessageBox.Show(Convert.ToInt32(dr["c"]).ToString());
                        // Showing correct value, ok
                }

                // Uncomment these lines to solve problem
                //con.Close();
                //OracleConnection.ClearAllPools();
                //con.Open();

                // Selecting all fields * from table
                com.CommandText = "SELECT * FROM Test";
                using (DbDataReader dr = com.ExecuteReader())
                {
                    MessageBox.Show(dr.GetSchemaTable().Rows.Count.ToString() + " / " + dr.FieldCount.ToString());
                    // HERE IS THE PROBLEM: message are showing 2/2, but table haves 3 fields

                    if (dr.Read())
                        MessageBox.Show(Convert.ToInt32(dr["c"]).ToString());
                    // Here throws IndexOutOfRangeException: Unable to find specified column in result set
                }
            }
        }
        finally
        {
            con.Close();
        }
    }
}

Answer 1

听起来当您执行阅读器时插入事务尚未提交。我认为您可以通过在插入后关闭连接并在执行阅读器之前再次打开连接来验证这一点（您可能需要使用 OracleConnection.ClearAllPools）

Answer 2

尝试使用OracleConnection.BeginTransaction 创建事务，然后在选择之前使用Commit，如文档中example 中所示。