blocks|key|2773787|text|两点：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2773788|2773789|DateTime.Now可以(潜在地)在每次调用时返回不同的日期。它也不是很快。通过只调用一次，您将获得更好的一致性和非常轻微的性能提升。|ordered-list-item|offset|length|style|CODE|2773790|你可能应该使用标准的方法来添加周和月，为了一致性(例如，一个月中并不总是有30天)和全球化(例如，不是所有的文化都有7天一周)。请注意，没有简单的方法可以单独使用DateTime添加周数；您必须使用Calendar来代替。|2773791|2773792|试试这个：|2773793|var+now+=+DateTime.UtcNow;+//+See+Jon+Skeet's+answer
var+cal+=+CultureInfo.InvariantCulture.Calendar;
if+(configEntity.GroupsLastrun+>+now.AddDays(-1)+&&+configEntity.Captureusersandgroups+==+"DAILY")+continue;
if+(configEntity.GroupsLastrun+>+cal.AddWeeks(now,+-1)+&&+configEntity.Captureusersandgroups+==+"WEEKLY")+continue;
if+(configEntity.GroupsLastrun+>+now.AddMonths(-1)+&&+configEntity.Captureusersandgroups+==+"MONTHLY")+continue;|code-block|syntax|javascript|2773794|或者只使用cal来处理所有事情：|2773795|var+now+=+DateTime.UtcNow;+//+See+Jon+Skeet's+answer
var+cal+=+CultureInfo.InvariantCulture.Calendar;
if+(configEntity.GroupsLastrun+>+cal.AddDays(now,+-1)+&&+configEntity.Captureusersandgroups+==+"DAILY")+continue;
if+(configEntity.GroupsLastrun+>+cal.AddWeeks(now,+-1)+&&+configEntity.Captureusersandgroups+==+"WEEKLY")+continue;
if+(configEntity.GroupsLastrun+>+cal.AddMonths(now,+-1)+&&+configEntity.Captureusersandgroups+==+"MONTHLY")+continue;|2773796|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/7y5k6h07.aspx^0|0|0|0|C|0|29|8|2R|8|2R|8|0|0|0|0|0|5|3|0|0^^$0|@$1|2|3|4|5|6|7|15|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|16|8|@]|9|@]|A|$]]|$1|C|3|D|5|E|7|17|8|@$F|18|G|19|H|I]]|9|@]|A|$]]|$1|J|3|K|5|E|7|1A|8|@$F|1B|G|1C|H|I]|$F|1D|G|1E|H|I]]|9|@$F|1F|G|1G|1|1H]]|A|$]]|$1|L|3|-4|5|6|7|1I|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|1J|8|@]|9|@]|A|$]]|$1|O|3|P|5|Q|7|1K|8|@]|9|@]|A|$R|S]]|$1|T|3|U|5|6|7|1L|8|@$F|1M|G|1N|H|I]]|9|@]|A|$]]|$1|V|3|W|5|Q|7|1O|8|@]|9|@]|A|$R|S]]|$1|X|3|-4|5|6|7|1P|8|@]|9|@]|A|$]]]|Y|$Z|$5|10|11|12|A|$13|14]]]]

Two points:

<ol>
<li><code>DateTime.Now</code> can (potential) return a different date every time it's called. It's also not very fast. You'll get better consistency and a very slight performance boost by only calling it once. </li>
<li>You should probably use the standard methods for adding weeks and months, for consistency (e.g. there's not always 30 days in a month) and globalization (e.g. not all cultures have a 7-day week). Note that there's no easy way to add weeks with a <code>DateTime</code> alone; you'll have to use a <a href="http://msdn.microsoft.com/en-us/library/7y5k6h07.aspx" rel="nofollow"><code>Calendar</code></a> instead.</li>
</ol>

Try this:

<pre><code>var now = DateTime.UtcNow; // See Jon Skeet's answer
var cal = CultureInfo.InvariantCulture.Calendar;
if (configEntity.GroupsLastrun &gt; now.AddDays(-1) &amp;&amp; configEntity.Captureusersandgroups == "DAILY") continue;
if (configEntity.GroupsLastrun &gt; cal.AddWeeks(now, -1) &amp;&amp; configEntity.Captureusersandgroups == "WEEKLY") continue;
if (configEntity.GroupsLastrun &gt; now.AddMonths(-1) &amp;&amp; configEntity.Captureusersandgroups == "MONTHLY") continue;
</code></pre>

Or just use <code>cal</code> for everything:

<pre><code>var now = DateTime.UtcNow; // See Jon Skeet's answer
var cal = CultureInfo.InvariantCulture.Calendar;
if (configEntity.GroupsLastrun &gt; cal.AddDays(now, -1) &amp;&amp; configEntity.Captureusersandgroups == "DAILY") continue;
if (configEntity.GroupsLastrun &gt; cal.AddWeeks(now, -1) &amp;&amp; configEntity.Captureusersandgroups == "WEEKLY") continue;
if (configEntity.GroupsLastrun &gt; cal.AddMonths(now, -1) &amp;&amp; configEntity.Captureusersandgroups == "MONTHLY") continue;
</code></pre>

blocks|key|648694|text|以下是几点：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|648695|648696|除非你想受时区和夏令时转换等的支配，否则我会使用DateTime.UtcNow而不是DateTime.Now+(并确保你也将UTC值存储为p.s.w.g+)|unordered-list-item|offset|length|style|CODE|648697|。如上所述，只需要询问当前日期/时间一次是值得的-但与性能相比，我会说重要的原因是一致性。在这种情况下，看起来你实际上只使用其中一个值，但在其他情况下，我见过人们编写同时使用两个求值的条件，如果在midnight|648698|You've上运行代码会导致问题，因为同时检查条件和确定截止日期而获得重复代码。我会把这两个分开。|648699|648700|所以，我会有这样的代码：|648701|//+Consider+whether+you+actually+want+DateTime.UtcNow.Date
DateTime+now+=+DateTime.UtcNow;

DateTime+deadline;
switch+(configEntity.Captureusersandgroups)
{
++++case+"DAILY":+deadline+=+now.AddDays(-1);
++++case+"WEEKYLY":+deadline+=+now.AddDays(-7);
++++case+"MONTHLY":+deadline+=+now.AddMonths(-1);
++++//+I'm+assuming+there's+*always*+a+schedule
++++default:+throw+new+InvalidOperationException("Invalid+schedule");
}
if+(configEntity.GroupsLastrun+>+deadline)
{
++++continue;
}|code-block|syntax|javascript|648702|请注意，从"now“中减去一个月与从"then”中添加一个月是不同的。例如，如果最后一次运行是在1月30日，那么使用上面的代码，下一次运行将不会是3月1日-而如果您将一个月添加到1月30日，则下一次运行将在2月28日(除非您使用这两个值的日期)。仔细考虑你想要的行为。|648703|(作为一个快速插件，我显然还建议将我的Noda+Time库用于日期/时间工作。它使任何特定值是本地时间，还是在某个时区等更清晰。)|648704|entityMap|0|LINK|mutability|MUTABLE|url|http://noda-time.googlecode.com/^0|0|0|O|F|16|C|0|0|0|0|0|0|0|J|9|0|0^^$0|@$1|2|3|4|5|6|7|17|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|18|8|@]|9|@]|A|$]]|$1|C|3|D|5|E|7|19|8|@$F|1A|G|1B|H|I]|$F|1C|G|1D|H|I]]|9|@]|A|$]]|$1|J|3|K|5|E|7|1E|8|@]|9|@]|A|$]]|$1|L|3|M|5|E|7|1F|8|@]|9|@]|A|$]]|$1|N|3|-4|5|6|7|1G|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|1H|8|@]|9|@]|A|$]]|$1|Q|3|R|5|S|7|1I|8|@]|9|@]|A|$T|U]]|$1|V|3|W|5|6|7|1J|8|@]|9|@]|A|$]]|$1|X|3|Y|5|6|7|1K|8|@]|9|@$F|1L|G|1M|1|1N]]|A|$]]|$1|Z|3|-4|5|6|7|1O|8|@]|9|@]|A|$]]]|10|$11|$5|12|13|14|A|$15|16]]]]

A few points:

<ul>
<li>Unless you want to be at the mercy of time zones and daylight saving transitions etc, I'd use <code>DateTime.UtcNow</code> rather than <code>DateTime.Now</code> (and make sure you store the UTC value as well)</li>
<li>As p.s.w.g. mentioned, it's worth only asking for the current date/time once - but rather than performance, I'd say that the important reason is for consistency. In this case it looks like you're only going to actually use one of the values, but in other cases I've seen people write conditions where two evaluations are used at the same time, leading to issues if the code is run over midnight</li>
<li>You've got repeated code due to checking the condition and determining the deadline at the same time. I'd separate the two.</li>
</ul>

So, I'd have code like this:

<pre><code>// Consider whether you actually want DateTime.UtcNow.Date
DateTime now = DateTime.UtcNow;

DateTime deadline;
switch (configEntity.Captureusersandgroups)
{
 case "DAILY": deadline = now.AddDays(-1);
 case "WEEKYLY": deadline = now.AddDays(-7);
 case "MONTHLY": deadline = now.AddMonths(-1);
 // I'm assuming there's *always* a schedule
 default: throw new InvalidOperationException("Invalid schedule");
}
if (configEntity.GroupsLastrun &gt; deadline)
{
 continue;
}
</code></pre>

Note that subtracting a month from "now" isn't the same as adding a month from "then". For example, if the last run was on January 30th, the next run won't be until March 1st using the above code - whereas if you added a month to January 30th, it would next be run on February 28th (unless you use the dates of both values). Consider carefully exactly the behaviour you want.

(As a quick plug, I'd also obviously recommend considering my <a href="http://noda-time.googlecode.com" rel="nofollow">Noda Time</a> library for date/time work. It makes it clearer whether any particular value is a local time, or in some time zone etc.)

blocks|key|6991|text|作为另一种方法，您可以将运行周期存储在enum中，如下所示：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|6992|enum+RunPeriod
{
++++Daily+=+1,
++++Weekly+=+7,
++++Monthly+=+30
}|code-block|syntax|javascript|6993|然后，您可以在数据库中存储int值，而不是string。这允许您在数据库端进行过滤，例如：|6994|var+configsToRun+=+
++++from+c+in+_myContext.Configs
++++where+EntityFunctions.AddDays(c.LastRun,(int)c.RunPeriod)+>+DateTime.Now);|6995|entityMap^0|J|4|0|0|D|3|L|6|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|M|3|N|5|H|7|Z|8|@]|D|@]|E|$I|J]]|$1|O|3|-4|5|6|7|10|8|@]|D|@]|E|$]]]|P|$]]

As an alternative approach, you could possibly store the run period in an <code>enum</code> like :

<pre><code>enum RunPeriod
{
 Daily = 1,
 Weekly = 7,
 Monthly = 30
}
</code></pre>

And then you can store the <code>int</code> values, instead of <code>string</code>, on the database. This allows you to do the filtering on the DB side, e.g.:

<pre><code>var configsToRun = 
 from c in _myContext.Configs
 where EntityFunctions.AddDays(c.LastRun,(int)c.RunPeriod) &gt; DateTime.Now);
</code></pre>

I have an object that is loading configurations from a database. I store the last time that a job was run with a datetime field (called <code>GroupsLastRun</code>) and I store how often the job should run with a string field called <code>Captureusersandgroups</code>. <code>Captureusersandgroups</code> stores three different types 'DAILY', 'WEEKLY' and 'MONTHLY'.

Basically, I have a loop should only continue if the job is due to run. So far I've got to the following point:

<pre><code>if (configEntity.GroupsLastrun &gt; DateTime.Now.AddDays(-1) &amp;&amp; configEntity.Captureusersandgroups == "DAILY") continue;
if (configEntity.GroupsLastrun &gt; DateTime.Now.AddDays(-7) &amp;&amp; configEntity.Captureusersandgroups == "WEEKLY") continue;
if (configEntity.GroupsLastrun &gt; DateTime.Now.AddDays(-30) &amp;&amp; configEntity.Captureusersandgroups == "MONTHLY") continue;
</code></pre>

I'm sure (certain) there's a much better approach to this but primarily being a SQL Server developer I lack the critical thinking / tools for approaching this. What is a better approach or what should I learn so I can think about this better?

Trying to compare today's date to a date a month ago

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我有一个从数据库加载配置的对象。我使用datetime字段(名为GroupsLastRun)存储作业的最后运行时间，并使用名为Captureusersandgroups的字符串字段存储作业运行的频率。Captureusersandgroups存储了三种不同的类型“每日”、“每周”和“每月”。基本上，我有一个循环应该只在...

问尝试将今天的日期与一个月前的日期进行比较
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问尝试将今天的日期与一个月前的日期进行比较EN