blocks|key|2720677|text|LinQ+to+entities+defers+execution+until+the+results+are+enumerated。因此，添加后续.Where()语句不会导致对db的多次调用|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2720678|var+docs+=+db.Documents
++++++++++++++++++.Where(d+=>
++++++++++++++++++++++db.EmployeeStatuses
+++++++++++++++++++++.Any(s+=>+s.EmpID+==+d.EmpID+&&+s.StatusEndDate+==+null+&&+s.Status+==+"Active")
++++++++++++++++++++++++);

if+(includeValid)
+++docs+=+docs.Where(x+=>+[condition]);

//...+and+so+on.

return+docs.ToList();+//+<-+This+is+where+the+query+is+actually+executed.+|code-block|syntax|javascript|2720679|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/bb738633.aspx^0|22|8|0|1U|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@$9|V|A|W|1|X]]|E|$]]|$1|F|3|G|5|H|7|Y|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Z|8|@]|D|@]|E|$]]]|L|$M|$5|N|O|P|E|$Q|R]]]]

<a href="http://msdn.microsoft.com/en-us/library/bb738633.aspx" rel="noreferrer">LinQ to entities defers execution until the results are enumerated</a>. Therefore, adding subsequent <code>.Where()</code> statements is not going to cause multiple calls to the db

<pre><code>var docs = db.Documents
 .Where(d =&gt;
 db.EmployeeStatuses
 .Any(s =&gt; s.EmpID == d.EmpID &amp;&amp; s.StatusEndDate == null &amp;&amp; s.Status == "Active")
 );

if (includeValid)
 docs = docs.Where(x =&gt; [condition]);

//... and so on.

return docs.ToList(); // &lt;- This is where the query is actually executed. 
</code></pre>

blocks|key|2720712|text|您可以使用PredicateBuilder实现。使用这个类，您可以在linq查询上应用一些过滤器。如下所示：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2720713|public+IEnumerable<Document>+GetDocumentsList(Guid?+sessionID,+bool?+includeValid,+bool?+includeExpired,+bool?++includeAboutToExpire)
{
++++var+query+=+db.Documents;

++++if+(sessionID.HasValue)
+++++++query+=+query.And(x+=>+x.SessionID+=+sessionID.Value);

++++if+(includeValid.HasValue+&&+includeValid.Value)
+++++++query+=+query.And(x+=>+x.IncludeValid+=+includeValid.Value);

++++//+others+parameters...

++++return+query.ToList();
}|code-block|syntax|javascript|2720714|PredicateBuilder实现|2720715|using+System;
using+System.Linq;
using+System.Linq.Expressions;
using+System.Collections.Generic;

public+static+class+PredicateBuilder
{
++public+static+Expression<Func<T,+bool>>+True<T>+()++{+return+f+=>+true;++}
++public+static+Expression<Func<T,+bool>>+False<T>+()+{+return+f+=>+false;+}

++public+static+Expression<Func<T,+bool>>+Or<T>+(this+Expression<Func<T,+bool>>+expr1,
++++++++++++++++++++++++++++++++++++++++++++++++++++++Expression<Func<T,+bool>>+expr2)
++{
++++var+invokedExpr+=+Expression.Invoke+(expr2,+expr1.Parameters.Cast<Expression>+());
++++return+Expression.Lambda<Func<T,+bool>>
++++++++++(Expression.OrElse+(expr1.Body,+invokedExpr),+expr1.Parameters);
++}

++public+static+Expression<Func<T,+bool>>+And<T>+(this+Expression<Func<T,+bool>>+expr1,
+++++++++++++++++++++++++++++++++++++++++++++++++++++++Expression<Func<T,+bool>>+expr2)
++{
++++var+invokedExpr+=+Expression.Invoke+(expr2,+expr1.Parameters.Cast<Expression>+());
++++return+Expression.Lambda<Func<T,+bool>>
++++++++++(Expression.AndAlso+(expr1.Body,+invokedExpr),+expr1.Parameters);
++}
}|2720716|entityMap|0|LINK|mutability|MUTABLE|url|http://www.albahari.com/nutshell/predicatebuilder.aspx^0|5|G|5|G|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@$9|Z|A|10|1|11]]|E|$]]|$1|F|3|G|5|H|7|12|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|13|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|14|8|@]|D|@]|E|$I|J]]|$1|O|3|-4|5|6|7|15|8|@]|D|@]|E|$]]]|P|$Q|$5|R|S|T|E|$U|V]]]]

You could use the <a href="http://www.albahari.com/nutshell/predicatebuilder.aspx" rel="nofollow"><code>PredicateBuilder</code></a> implementation. With this class you can apply some filters on your linq queries. Something like this:

<pre><code>public IEnumerable&lt;Document&gt; GetDocumentsList(Guid? sessionID, bool? includeValid, bool? includeExpired, bool? includeAboutToExpire)
{
 var query = db.Documents;

 if (sessionID.HasValue)
 query = query.And(x =&gt; x.SessionID = sessionID.Value);

 if (includeValid.HasValue &amp;&amp; includeValid.Value)
 query = query.And(x =&gt; x.IncludeValid = includeValid.Value);

 // others parameters...

 return query.ToList();
}
</code></pre>

<h2>PredicateBuilder implementation</h2>

<pre><code>using System;
using System.Linq;
using System.Linq.Expressions;
using System.Collections.Generic;

public static class PredicateBuilder
{
 public static Expression&lt;Func&lt;T, bool&gt;&gt; True&lt;T&gt; () { return f =&gt; true; }
 public static Expression&lt;Func&lt;T, bool&gt;&gt; False&lt;T&gt; () { return f =&gt; false; }

 public static Expression&lt;Func&lt;T, bool&gt;&gt; Or&lt;T&gt; (this Expression&lt;Func&lt;T, bool&gt;&gt; expr1,
 Expression&lt;Func&lt;T, bool&gt;&gt; expr2)
 {
 var invokedExpr = Expression.Invoke (expr2, expr1.Parameters.Cast&lt;Expression&gt; ());
 return Expression.Lambda&lt;Func&lt;T, bool&gt;&gt;
 (Expression.OrElse (expr1.Body, invokedExpr), expr1.Parameters);
 }

 public static Expression&lt;Func&lt;T, bool&gt;&gt; And&lt;T&gt; (this Expression&lt;Func&lt;T, bool&gt;&gt; expr1,
 Expression&lt;Func&lt;T, bool&gt;&gt; expr2)
 {
 var invokedExpr = Expression.Invoke (expr2, expr1.Parameters.Cast&lt;Expression&gt; ());
 return Expression.Lambda&lt;Func&lt;T, bool&gt;&gt;
 (Expression.AndAlso (expr1.Body, invokedExpr), expr1.Parameters);
 }
}
</code></pre>

blocks|key|4186891|text|看起来你需要连接文档和状态。此外，条件(!includeValid+%7C%7C+d.Valid)还为您提供了仅id+includeValid为true的有效文档过滤功能|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4186892|public+List<Document>+GetDocumentsList(Guid+sessionID,+
+++++++bool+includeValid,+bool+includeExpired,+bool+includeAboutToExpire)
{
+++using+(DB+db+=+new+DB())
+++{
+++++++//+get+the+active+documents
+++++++var+docs+=+from+d+in+db.Documents
++++++++++++++++++join+s+in+db.EmployeeStatuses+on+d.EmpID+equals+s.EmpID
++++++++++++++++++where+s.StatusEndDate+==+null+&&
++++++++++++++++++++++++s.Status+==+"Active"+&&
++++++++++++++++++++++++(!includeValid+%7C%7C+d.Valid)+&&
++++++++++++++++++++++++(!includeExpired+%7C%7C+d.Expired)+&&
++++++++++++++++++++++++(!includeAboutToExpired+%7C%7C+d.AboutToExpired)
++++++++++++++++++select+d;

++++++++return+docs.ToList()
++++}
}|code-block|syntax|javascript|4186893|entityMap^0|J|Q|1J|C|1W|4|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|T|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|U|8|@]|D|@]|E|$]]]|L|$]]

Looks like you need join of documents and statuses. Also condition <code>(!includeValid || d.Valid)</code> gives you filtering of valid documents only id <code>includeValid</code> is <code>true</code>:

<pre><code>public List&lt;Document&gt; GetDocumentsList(Guid sessionID, 
 bool includeValid, bool includeExpired, bool includeAboutToExpire)
{
 using (DB db = new DB())
 {
 // get the active documents
 var docs = from d in db.Documents
 join s in db.EmployeeStatuses on d.EmpID equals s.EmpID
 where s.StatusEndDate == null &amp;&amp;
 s.Status == "Active" &amp;&amp;
 (!includeValid || d.Valid) &amp;&amp;
 (!includeExpired || d.Expired) &amp;&amp;
 (!includeAboutToExpired || d.AboutToExpired)
 select d;

 return docs.ToList()
 }
}
</code></pre>

blocks|key|4186911|text|像这样的怎么样？(当然，我是在假设如何评估这些标志)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4186912|public+List<Document>+GetDocumentsList(Guid+sessionID,+bool+includeValid,+bool+includeExpired,+bool+includeAboutToExpire)
{
+++using+(DB+db+=+new+DB())
+++{
+++++++//+get+the+active+documents
+++++++var+docs+=+db.Documents
++++++++++++++++++.Where(d+=>
++++++++++++++++++++++db.EmployeeStatuses
+++++++++++++++++++++.Any(s+=>+s.EmpID+==+d.EmpID+
+++++++++++++++++++++++++++++++&&+s.StatusEndDate+==+null+
+++++++++++++++++++++++++++++++&&+(s.Status+==+"Active"
+++++++++++++++++++++++++++++++++%7C%7C+(includeValid+&&+s.Status+==+"Valid")
+++++++++++++++++++++++++++++++++%7C%7C+(includeExpired+&&+s.Status+==+"Expired")
+++++++++++++++++++++++++++++++++%7C%7C+(includeAboutToExpired+&&+s.Status+==+"AboutToExpired")+))
++++++++++++++++++++++++);

++++++++//+how+to+filter+the+result+depending+on+includeValid,+includeExpired+and+includeAboutToExpired+parameters?

++++++++return+docs.ToList()
++++}
}|code-block|syntax|javascript|4186913|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|$]]

what about something like this? (I'm making assumptions on how those flags are supposed to be evaluated of course). 

<pre><code>public List&lt;Document&gt; GetDocumentsList(Guid sessionID, bool includeValid, bool includeExpired, bool includeAboutToExpire)
{
 using (DB db = new DB())
 {
 // get the active documents
 var docs = db.Documents
 .Where(d =&gt;
 db.EmployeeStatuses
 .Any(s =&gt; s.EmpID == d.EmpID 
 &amp;&amp; s.StatusEndDate == null 
 &amp;&amp; (s.Status == "Active"
 || (includeValid &amp;&amp; s.Status == "Valid")
 || (includeExpired &amp;&amp; s.Status == "Expired")
 || (includeAboutToExpired &amp;&amp; s.Status == "AboutToExpired") ))
 );

 // how to filter the result depending on includeValid, includeExpired and includeAboutToExpired parameters?

 return docs.ToList()
 }
}
</code></pre>

I have the follwoing method to return some data for me:

<pre><code>public List&lt;Document&gt; GetDocumentsList(Guid sessionID, bool includeValid, bool includeExpired, bool includeAboutToExpire)
{
 using (DB db = new DB())
 {
 // get the active documents
 var docs = db.Documents
 .Where(d =&gt;
 db.EmployeeStatuses
 .Any(s =&gt; s.EmpID == d.EmpID &amp;&amp; s.StatusEndDate == null &amp;&amp; s.Status == "Active")
 );

 // how to filter the result depending on includeValid, includeExpired and includeAboutToExpired parameters?

 return docs.ToList()
 }
}
</code></pre>

The problem here is, I want to filter the result depending on the <code>bool</code> parametes, for example if <code>includeValid</code> is true, then the valid documents will be included, if the <code>includeExpired</code> is true then the expired documents will be included and so on, I could have all three true or one or two of them are true. I do not want to have more than one call to the DB. Is there a logic that can do this with one call?

Filtering Linq query depending on some parameters

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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我有下面的方法为我返回一些数据：public List<Document> GetDocumentsList(Guid sessionID, bool includeValid, bool includeExpired, bool includeAboutToExpire){ using (DB db = new ...

问根据某些参数过滤Linq查询
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