如何使用实体框架执行IsNull? [英] How do I do an IsNull with entity framework?

问题描述

我有一个显示单个记录的结果页.

问题:
如果没有电话分机，如何排除(抑制)电话分机本身和分机".返回数据中的标签?

如果有扩展名，我想要:
•克里斯·康普顿919-754-6000转. 6512 [e-mail]
其他
•克里斯·康普顿919-754-6512 [e-mail]

如果本周没有答案，我将其编码为t-sql存储的proc，如下所示:

I have a results page that displays a single record.

Question:
If there isn''t a phone extension, how do I exclude (suppress) the phone extension itself and "ext." label from the returned data?

If there is an extension I want:
• Chris Compton 919-754-6000 ext. 6512 [e-mail]
else
• Chris Compton 919-754-6512 [e-mail]

If I don''t get an answer this week I''ll just code it into a t-sql stored proc like this:

SELECT ..., Phone, IsNull(''ext. ''+nullif([PhoneExt],''''), ''''), Email ...

(但我宁愿将该逻辑保留在数据库之外)

这是我所能(简化)的，但标签为"ext".始终显示:

(but I''d rather keep that logic out of the database)

Here''s what I have (shortened) that works, but the label "ext." always shows:

try { pk = Convert.ToInt32(Request.QueryString["id"]); }
catch (Exception) { pk = 0; }

var query = (
    from c in context.tEmployees
    where (c.pkEmployee == pk)
    orderby c.NameLast, c.NameFirst, c.NameMiddle, c.Agency
    select new
    {   Name = c.First + " " + c.Last,
        Telephone = c.Phone ,
        TelephoneExt = " ext. " + c.PhoneExt,
        Email = c.Email }
    );

if (query.Count() == 1)
{   ResultsRepeater.DataSource = query;
    ResultsRepeater.DataBind();
}
else
{ Response.Write("I'm sorry we could not find that employee, please try the search page again."); }

另外，如果有更好的方法来处理变量"pk"，我欢迎提出建议.

注意:t-sql和代码都可以工作.如果我引入了错误，请缩短代码以向我道歉.

编辑6/7/12:
以下所有三种解决方案都很棒，对我有帮助！
在昨天结束之前，我及时看到了第一个答案及时部署工作代码(在质量检查中).
我实际上是今天早上换到第二个(我尽量避免在if子句中使用"not").
阅读第3条(和评论)后，我做了一些改进.
再次感谢！
-Chris C. 12/5/7下午EDT

Also, if there''s a better way to handle the variable "pk" I''m open to suggestions.

NOTE: that the t-sql and the code both work. If I''ve introduced an error shortening the code to post the question my apologies.

Edit 6/7/12:
ALL THREE solutions below are great and helped me!
I saw the first answer in time to deploy the working code (in QA) just before the end of my day yesterday.
I actually changed to the second one this morning (I try to avoid using "not" in an if clause).
I made a couple more improvements after reading number three (and the comments).
Thanks again!
-Chris C. 5/7/12 1 PM EDT

推荐答案

有关:

TelephoneExt = string.IsNullOrEmpty(c.PhoneExt) ? " ext. " + c.PhoneExt : string.Empty;

Clifford为IsNull问题提供了正确的解决方案，但我认为我想添加一种解析整数的替代方法:

Clifford has the correct solution for the IsNull issue, but I thought I''d add an alternative way to parse the integer:

if (!Int32.TryParse(Request.QueryString["id"], out pk))
{
    // The TryParse will default it to 0 on failure,
    // but I put this here in case you want to default to something else.
    pk = 0;
}

var query = (
    from c in context.tEmployees
    where (c.pkEmployee == pk)
    orderby c.NameLast, c.NameFirst, c.NameMiddle, c.Agency
    select new
    {   Name = c.First + " " + c.Last,
        Telephone = c.Phone ,
        TelephoneExt = c.PhoneExt != null ? " ext. " + c.PhoneExt : string.Empty,
        Email = c.Email }
    );

或

or

var query = (
    from c in context.tEmployees
    where (c.pkEmployee == pk)
    orderby c.NameLast, c.NameFirst, c.NameMiddle, c.Agency
    select new
    {   Name = c.First + " " + c.Last,
        Telephone = c.Phone ,
        TelephoneExt = ! string.IsNullOrEmpty(c.PhoneExt) ? " ext. " + .PhoneExt : string.Empty,
        Email = c.Email }
    );

这篇关于如何使用实体框架执行IsNull?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IT屋！