blocks|key|1389591|text|实体框架的另一个示例：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1389592|var+customers+=+db.Customers
++++++++++++++++++.Where(c+=>+c.IsActive)
++++++++++++++++++.OrderBy(c+=>+Guid.NewGuid())
++++++++++++++++++.FirstOrDefault();|code-block|syntax|javascript|1389593|这不适用于LINQ+to+SQL。OrderBy只是被丢弃了。|offset|length|style|CODE|1389594|entityMap^0|0|0|H|7|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@$I|R|J|S|K|L]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

Another sample for Entity Framework:

<pre><code>var customers = db.Customers
 .Where(c =&gt; c.IsActive)
 .OrderBy(c =&gt; Guid.NewGuid())
 .FirstOrDefault();
</code></pre>

This does not work with LINQ to SQL. The <code>OrderBy</code> is simply being dropped.

blocks|key|1389733|text|如果你想从表中获得var+count+=+16随机行，你可以这样写|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1389734|var+rows+=+Table.OrderBy(t+=>+Guid.NewGuid())
++++++++++++++++++++++++.Take(count);|code-block|syntax|javascript|1389735|在这里，我使用了E.F，表是一个Dbset|1389736|entityMap^0|9|E|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|S|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|N|$]]

if you want to get e.g. <code>var count = 16</code> random rows from table, you can write

<pre><code>var rows = Table.OrderBy(t =&gt; Guid.NewGuid())
 .Take(count);
</code></pre>

here I used E.F, and the Table is a Dbset

blocks|key|1604597|text|如果获取随机行的目的是抽样，我已经非常简要地谈到了微软研究团队Larson等人的一种很好的方法，他们使用物化视图为Sql+Server开发了一个抽样框架。还有一个到实际论文的链接。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1604598|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

If the purpose of getting random rows is sampling, I have talked very briefly <a href="http://qualityofdata.com/2011/02/13/sampling-data-with-sql-server/" rel="nofollow">here</a> about a nice approach from Larson et al., Microsoft Research team where they have developed a sampling framework for Sql Server using materialized views. There is a link to the actual paper also.

blocks|key|1604664|text|我对DataTables进行了随机函数查询：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1604665|var+result+=+(from+result+in+dt.AsEnumerable()
++++++++++++++order+by+Guid.NewGuid()
++++++++++++++select+result).Take(3);+|code-block|syntax|javascript|1604666|entityMap^0|2|9|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

I have random function query against <code>DataTable</code>s:

<pre><code>var result = (from result in dt.AsEnumerable()
 order by Guid.NewGuid()
 select result).Take(3); 
</code></pre>

blocks|key|1389852|text|我在这里想知道如何从少数用户中获得几个随机页面，以便每个用户获得一些不同的随机3个页面。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1389853|这是我的最终解决方案，在Sharepoint+2010中使用LINQ查询页面列表。它是用Visual+Basic编写的，对不起:p|1389854|Dim+Aleatorio+As+New+Random()

Dim+Paginas+=+From+a+As+SPListItem+In+Sitio.RootWeb.Lists("Páginas")+Order+By+Aleatorio.Next+Take+3|code-block|syntax|javascript|1389855|在查询大量结果之前，可能应该进行一些分析，但这对我的目的来说是完美的|1389856|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|O|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Came here wondering how to get a few random pages from a small number of them, so each user gets some different random 3 pages. 

This is my final solution, working querying with LINQ against a list of pages in Sharepoint 2010. It's in Visual Basic, sorry :p

<pre><code>Dim Aleatorio As New Random()

Dim Paginas = From a As SPListItem In Sitio.RootWeb.Lists("Páginas") Order By Aleatorio.Next Take 3
</code></pre>

Probably should get some profiling before querying a great number of results, but it's perfect for my purpose

blocks|key|1604770|text|在LINQPad中使用LINQ+to+SQL作为C#语句，如下所示|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1604771|IEnumerable<Customer>+customers+=+this.ExecuteQuery<Customer>(@"SELECT+top+10+*+from+[Customers]+order+by+newid()");
customers.Dump();|code-block|syntax|javascript|1604772|生成的SQL为|1604773|SELECT+top+10+*+from+[Customers]+order+by+newid()|1604774|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Using LINQ to SQL in LINQPad as C# statements look like

<pre><code>IEnumerable&lt;Customer&gt; customers = this.ExecuteQuery&lt;Customer&gt;(@"SELECT top 10 * from [Customers] order by newid()");
customers.Dump();
</code></pre>

The generated SQL is

<pre><code>SELECT top 10 * from [Customers] order by newid()
</code></pre>

blocks|key|1604828|text|下面的示例将调用源以检索计数，然后在源上应用一个介于0和n之间的数字的跳过表达式。第二个方法将通过使用随机对象(它将对内存中的所有内容进行排序)来应用顺序，并选择传递到方法调用中的数字。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1604829|public+static+class+IEnumerable
{
++++static+Random+rng+=+new+Random((int)DateTime.Now.Ticks);

++++public+static+T+RandomElement<T>(this+IEnumerable<T>+source)
++++{
++++++++T+current+=+default(T);
++++++++int+c+=+source.Count();
++++++++int+r+=+rng.Next(c);
++++++++current+=+source.Skip(r).First();
++++++++return+current;
++++}

++++public+static+IEnumerable<T>+RandomElements<T>(this+IEnumerable<T>+source,+int+number)
++++{
++++++++return+source.OrderBy(r+=>+rng.Next()).Take(number);
++++}
}|code-block|syntax|javascript|1604830|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

The example below will call the source to retrieve a count and then apply a skip expression on the source with a number between 0 and n. The second method will apply order by using the random object (which will order everything in memory) and select the number passed into the method call. 

<pre><code>public static class IEnumerable
{
 static Random rng = new Random((int)DateTime.Now.Ticks);

 public static T RandomElement&lt;T&gt;(this IEnumerable&lt;T&gt; source)
 {
 T current = default(T);
 int c = source.Count();
 int r = rng.Next(c);
 current = source.Skip(r).First();
 return current;
 }

 public static IEnumerable&lt;T&gt; RandomElements&lt;T&gt;(this IEnumerable&lt;T&gt; source, int number)
 {
 return source.OrderBy(r =&gt; rng.Next()).Take(number);
 }
}
</code></pre>

blocks|key|1604870|text|我使用这个方法来获取随机的新闻，它工作得很好;)|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1604871|++++public+string+LoadRandomNews(int+maxNews)
++++{
++++++++string+temp+=+"";

++++++++using+(var+db+=+new+DataClassesDataContext())
++++++++{
++++++++++++var+newsCount+=+(from+p+in+db.Tbl_DynamicContents
+++++++++++++++++++++++++++++where+p.TimeFoPublish.Value.Date+<=+DateTime.Now
+++++++++++++++++++++++++++++select+p).Count();
++++++++++++int+i;
++++++++++++if+(newsCount+<+maxNews)
++++++++++++++++i+=+newsCount;
++++++++++++else+i+=+maxNews;
++++++++++++var+r+=+new+Random();
++++++++++++var+lastNumber+=+new+List<int>();
++++++++++++for+(;+i+>+0;+i--)
++++++++++++{
++++++++++++++++int+currentNumber+=+r.Next(0,+newsCount);
++++++++++++++++if+(!lastNumber.Contains(currentNumber))
++++++++++++++++{+lastNumber.Add(currentNumber);+}
++++++++++++++++else
++++++++++++++++{
++++++++++++++++++++while+(true)
++++++++++++++++++++{
++++++++++++++++++++++++currentNumber+=+r.Next(0,+newsCount);
++++++++++++++++++++++++if+(!lastNumber.Contains(currentNumber))
++++++++++++++++++++++++{
++++++++++++++++++++++++++++lastNumber.Add(currentNumber);
++++++++++++++++++++++++++++break;
++++++++++++++++++++++++}
++++++++++++++++++++}
++++++++++++++++}
++++++++++++++++if+(currentNumber+==+newsCount)
++++++++++++++++++++currentNumber--;
++++++++++++++++var+news+=+(from+p+in+db.Tbl_DynamicContents
++++++++++++++++++++++++++++orderby+p.ID+descending
++++++++++++++++++++++++++++where+p.TimeFoPublish.Value.Date+<=+DateTime.Now
++++++++++++++++++++++++++++select+p).Skip(currentNumber).Take(1).Single();
++++++++++++++++temp+%2B=
++++++++++++++++++++string.Format("<div+class=\"divRandomNews\"><img+src=\"files/1364193007_news.png\"+class=\"randomNewsImg\"+/>"+%2B
++++++++++++++++++++++++++++++++++"<a+class=\"randomNews\"+href=\"News.aspx?id={0}\"+target=\"_blank\">{1}</a></div>",
++++++++++++++++++++++++++++++++++news.ID,+news.Title);
++++++++++++}
++++++++}
++++++++return+temp;
++++}|code-block|syntax|javascript|1604872|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

i use this method for take random news and its work fine ;)

<pre><code> public string LoadRandomNews(int maxNews)
 {
 string temp = "";

 using (var db = new DataClassesDataContext())
 {
 var newsCount = (from p in db.Tbl_DynamicContents
 where p.TimeFoPublish.Value.Date &lt;= DateTime.Now
 select p).Count();
 int i;
 if (newsCount &lt; maxNews)
 i = newsCount;
 else i = maxNews;
 var r = new Random();
 var lastNumber = new List&lt;int&gt;();
 for (; i &gt; 0; i--)
 {
 int currentNumber = r.Next(0, newsCount);
 if (!lastNumber.Contains(currentNumber))
 { lastNumber.Add(currentNumber); }
 else
 {
 while (true)
 {
 currentNumber = r.Next(0, newsCount);
 if (!lastNumber.Contains(currentNumber))
 {
 lastNumber.Add(currentNumber);
 break;
 }
 }
 }
 if (currentNumber == newsCount)
 currentNumber--;
 var news = (from p in db.Tbl_DynamicContents
 orderby p.ID descending
 where p.TimeFoPublish.Value.Date &lt;= DateTime.Now
 select p).Skip(currentNumber).Take(1).Single();
 temp +=
 string.Format("&lt;div class=\"divRandomNews\"&gt;&lt;img src=\"files/1364193007_news.png\" class=\"randomNewsImg\" /&gt;" +
 "&lt;a class=\"randomNews\" href=\"News.aspx?id={0}\" target=\"_blank\"&gt;{1}&lt;/a&gt;&lt;/div&gt;",
 news.ID, news.Title);
 }
 }
 return temp;
 }
</code></pre>

blocks|key|1390060|text|var+cust+=+(from+c+in+ctx.CUSTOMERs.ToList()+select+c).OrderBy(x+=>+x.Guid.NewGuid()).Taket(2);|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1390061|随机选择2行|unstyled|1390062|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|J|8|@]|9|@]|A|$]]|$1|G|3|-4|5|F|7|K|8|@]|9|@]|A|$]]]|H|$]]

<pre><code>var cust = (from c in ctx.CUSTOMERs.ToList() select c).OrderBy(x =&gt; x.Guid.NewGuid()).Taket(2);
</code></pre>

Select random 2 row

blocks|key|1390124|text|添加到Marc+Gravell的解决方案中如果您没有使用datacontext类本身(因为您以某种方式代理它，例如为了测试目的而伪造datacontext+)，则不能直接使用定义的UDF+:它不会被编译成SQL，因为您没有在实际数据上下文类的子类或分部类中使用它。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1390125|此问题的解决方法是在代理中创建随机化函数，为其提供要随机化的查询：|1390126|public+class+DataContextProxy+:+IDataContext
{
++++private+readonly+DataContext+_context;

++++public+DataContextProxy(DataContext+context)
++++{
++++++++_context+=+context;
++++}

++++//+Snipped+irrelevant+code

++++public+IOrderedQueryable<T>+Randomize<T>(IQueryable<T>+query)
++++{
++++++++return+query.OrderBy(x+=>+_context.Random());
++++}
}|code-block|syntax|javascript|1390127|下面是如何在你的代码中使用它：|1390128|var+query+=+_dc.Repository<SomeEntity>();
query+=+_dc.Randomize(query);|1390129|为了完整，下面是如何在伪datacontext+(在内存实体中使用)中实现这一点：|1390130|public+IOrderedQueryable<T>+Randomize<T>(IQueryable<T>+query)
{
++++return+query.OrderBy(x+=>+Guid.NewGuid());
}|1390131|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|V|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|W|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|X|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|Y|8|@]|9|@]|A|$G|H]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

To add to Marc Gravell's solution. If you are not working with the datacontext class itself (because you proxy it somehow e.g. to fake the datacontext for testing purposes), you cannot use the defined UDF directly: it will not be compiled to SQL because you're not using it in a subclass or partial class of your real data context class. 

A workaround for this problem is to create a Randomize function in your proxy, feeding it with the query you want to be randomized:

<pre><code>public class DataContextProxy : IDataContext
{
 private readonly DataContext _context;

 public DataContextProxy(DataContext context)
 {
 _context = context;
 }

 // Snipped irrelevant code

 public IOrderedQueryable&lt;T&gt; Randomize&lt;T&gt;(IQueryable&lt;T&gt; query)
 {
 return query.OrderBy(x =&gt; _context.Random());
 }
}
</code></pre>

Here is how you'd use it in your code:

<pre><code>var query = _dc.Repository&lt;SomeEntity&gt;();
query = _dc.Randomize(query);
</code></pre>

To be complete, this is how to implement this in the FAKE datacontext (which uses in memory entities):

<pre><code>public IOrderedQueryable&lt;T&gt; Randomize&lt;T&gt;(IQueryable&lt;T&gt; query)
{
 return query.OrderBy(x =&gt; Guid.NewGuid());
}
</code></pre>

What is the best (and fastest) way to retrieve a random row using Linq to SQL when I have a condition, e.g. some field must be true?

Random row from Linq to Sql

当我有一个条件，例如某些字段必须为真时，使用Linq to SQL检索随机行的最佳(最快)方法是什么？

问从Linq到Sql的随机行
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回答 10

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