SQL Server：DateTime 数据导致 DateTime.Today 异常错误

Question

我创建了以下导致错误状态的序列

System.IndexOutOfRangeException: '索引超出了数组的范围。'

如 cmets 所示。

SqlCommand cmd = new SqlCommand(@"SELECT GETDATE() 'Today', DATENAME(weekday, GETDATE()) 'Day Name'; 
          select * from [Schedule] where Working = datename(weekday,GetDate()) and Commencing != Finishing; 
          select * from [Vacation] where VacStart = GetDate();", con);

con.Open();

SqlDataReader read = cmd.ExecuteReader();
DateTime now = DateTime.Today;

while (read.Read())
{
    // from Schedule Table
    string Working = read.GetString(1);
    DateTime Commencing = read.GetDateTime(2); //Exception Error Here
    DateTime Finishing = read.GetDateTime(3); //Exception Error Here

    // from Vacation Table
    string Reason = read.GetString(1);

    if (Reason == null)
    {
        // if condition is met
        lblMsg2.Text = "<p class='closed'>Sorry, we are closed for for a personal holiday.<br />If you are a current client and this is an emergency, we will of course make every effort to accommodate you.</p>";
    }
    else
    {
        // if condition is not met
        if (Working != null && now >= Commencing && Finishing <= now)
        {
            // if condition met
            lblMsg2.Text = "<p class='open'>Yes, we are currently open and would love to hear from you!</p>";
        }
        else
        {
            // if condition is not met
            lblMsg2.Text = "<p class='closed'>Sorry, we are currently closed. You can reach us during normal business hours. We would love to have the opportunity to speak with you!</p>";
        }
    }
}

根据我对大量帖子的研究，我认为错误是由日期差异引起的，即 1900-01-01 与 2018-07-18。日期不相关，因为我只是想比较时间。

我尝试了几种变体，您可以在其中更改查询以考虑日期，但我无法让这些工作。

看起来每个人都将数据从 DateTime 转换为字符串，我也很难开始工作。

Commencing 和 Finishing 列在 SQL Server 数据库中都是 DateTime 类型。

Answer 1

SqlCommand 中的查询包含 3 个选择语句，因此它将返回 3 个行集。您遇到的问题是发布的代码仅处理第一个行集；但评论表明您认为它正在处理第二个和第三个。我的解决方案如下；但这里列出了一些改进建议。

1. SqlCommand、SqlDataReader 和 SqlConnection 都是 IDisposable，所以每个都应该在 using 块中。 （我接受我在发布的代码中看不到连接，我只是在猜测。）
2. 根据 cmets，您似乎不关心 3 个查询中的第一个，所以不要让 SQL 来做。
3. 避免使用select *。如果您专门编写了您期望的列，那么您的代码将受到保护，不会对数据库进行更改，例如更改列的顺序或向表中添加新列。它还可以帮助您检查代码，因为您将能够检查每个序数所指的列。
4. 鉴于您已经完成了select *，我无法确定您是否知道 DataReader 上的 Get 方法的序号从零开始，而不是 1，所以我想我应该提一下它 - 如果有问题，您需要修复它。
5. 如果一列返回null，那么你不能Get它，你需要对相同的序数使用IsDbNull方法。您可以将这两个调用封装在一个扩展方法中。如下所示。
6. 我建议将read（动词）重命名为reader（名词）。
7. 要从一个结果集前进到下一个结果集，请使用NextResult()

这里是扩展方法，其他类型可以做类似的方法：

public static class DataRecordExtensions
{
    public static string GetNullableString(this IDataRecord dataRecord, int ordinal)
    {
        return dataRecord.IsDBNull(ordinal) ? null : dataRecord.GetString(ordinal);
    }
}

注意：我无法从 sn-p 中得知查询返回了多少行，所以我只使用了 while 循环。我已将逻辑转移到更接近相关代码；但它应该表现相同。无论如何，逻辑可能需要修复，因为我不知道返回了多少行。

    using (SqlCommand cmd = new SqlCommand(@"select * from [Schedule] where Working = datename(weekday,GetDate()) and Commencing != Finishing; 
      select * from [Vacation] where VacStart = GetDate();", con))
    {
        con.Open();

        using (SqlDataReader reader = cmd.ExecuteReader())
        {
            DateTime now = DateTime.Today;

            // from Schedule Table
            while (reader.Read())
            {
                string working = reader.GetString(1);
                DateTime commencing = reader.GetDateTime(2);
                DateTime finishing = reader.GetDateTime(3);

                // if condition is not met
                if (working != null && now >= commencing && finishing <= now)
                {
                    // if condition met
                    lblMsg2.Text = "<p class='open'>Yes, we are currently open and would love to hear from you!</p>";
                }
                else
                {
                    // if condition is not met
                    lblMsg2.Text = "<p class='closed'>Sorry, we are currently closed. You can reach us during normal business hours. We would love to have the opportunity to speak with you!</p>";
                }
            }

            // from Vacation Table
            if (reader.NextResult())
            {
                while (reader.Read())
                {
                    string reason = reader.GetNullableString(1);
                    if (reason == null)
                    {
                        // if condition is met
                        lblMsg2.Text = "<p class='closed'>Sorry, we are closed for for a personal holiday.<br />If you are a current client and this is an emergency, we will of course make every effort to accommodate you.</p>";
                    }
                }
            }
        }