问题描述

我有一个包含两列的表 - [security_role_name] 和 security_role_cd .security_role_cd 的数据类型是 Security_Role 表中的 smallint.

I have a table with two column - [security_role_name] and security_role_cd . Datatype for security_role_cd is smallint in Security_Role table.

我有以下数据选择逻辑.返回的数据类型因数据的场景而异:-

I have following data selection logic. The datatype returned varies based on the scenario of data:-

1. 表格中没有数据
2. 表格中有一条记录

问题

1. 为什么在这些场景中数据类型会有所不同
2. 如何改正

注意:目前我正在使用 try..catch 来满足这种情况

Note: Currently i am using try..catch to meet this scenario

代码

    private int GetNextRoleID(SqlConnection connection)
    {
        int? newRoleID = null;
        //string commandText = "SELECT  (MAX(security_role_cd)) AS [NewRoleID] FROM Security_Role ";
        string commandText = "SELECT  TOP 1 security_role_cd AS [NewRoleID] FROM Security_Role ORDER BY security_role_cd DESC";
        SqlCommand command = new SqlCommand(commandText, connection);
        command.CommandType = System.Data.CommandType.Text;
        SqlDataReader reader = command.ExecuteReader();
        if (reader.HasRows)
        {
            while (reader.Read())
            {
                if (!reader.IsDBNull(0))
                {
                    //newRoleID = Convert.ToInt32((reader.GetInt16(0)) + 1);

                    try
                    {
                        newRoleID = Convert.ToInt32(reader.GetInt16(0)) + 1;
                    }
                    catch
                    {
                        int result = (reader.GetInt32(0));
                        newRoleID = result + 1;
                    }
                }
            }
        }
        reader.Close();

        if (newRoleID == null)
        {
            newRoleID = 1;
        }

        return (Convert.ToInt32(newRoleID));

    }

参考:

1. 如何使用 ADO.NET 获取表中列的 SqlDbType?

推荐答案

可以看reader.GetFieldType(0).例如:

    int i;
    switch (Type.GetTypeCode(reader.GetFieldType(0)))
    {
        case TypeCode.Int16: i = reader.GetInt16(0); break;
        case TypeCode.Int32: i = reader.GetInt32(0); break;
        // TODO: any other cases you need to handle
        default: throw new NotSupportedException();
    }

或者更简单:

    int i = Convert.ToInt32(reader.GetValue(0));

这篇关于返回的数据类型因表中的数据而异的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持编程学习网！