blocks|key|686012|text|只需像处理任何其他需要执行布尔逻辑的语句一样使用&&运算符。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|686013|if+(useAdditionalClauses)
{
++results+=+results.Where(
++++++++++++++++++o+=>+o.OrderStatus+==+OrderStatus.Open+
++++++++++++++++++&&+o.CustomerID+==+customerID)+++++
}|code-block|syntax|javascript|686014|entityMap^0|O|2|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|$]]

Just use the <code>&amp;&amp;</code> operator like you would with any other statement that you need to do boolean logic.

<pre><code>if (useAdditionalClauses)
{
 results = results.Where(
 o =&gt; o.OrderStatus == OrderStatus.Open 
 &amp;&amp; o.CustomerID == customerID) 
}
</code></pre>

blocks|key|686108|text|您可以像以前一样继续链接它们。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|686109|results+=+results.Where+(o+=>+o.OrderStatus+==+OrderStatus.Open);
results+=+results.Where+(o+=>+o.InvoicePaid);|code-block|syntax|javascript|686110|这表示一个AND。|686111|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

You can continue chaining them like you've done.

<pre><code>results = results.Where (o =&gt; o.OrderStatus == OrderStatus.Open);
results = results.Where (o =&gt; o.InvoicePaid);
</code></pre>

This represents an AND.

blocks|key|686147|text|results+=+context.Orders.Where(o+=>+o.OrderDate+<=+today+&&+today+<=+o.OrderDate)|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|686148|选择未添加，因为您已在处理订单。|unstyled|686149|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>results = context.Orders.Where(o =&gt; o.OrderDate &lt;= today &amp;&amp; today &lt;= o.OrderDate)
</code></pre>

The select is uneeded as you are already working with an order.

blocks|key|686206|text|两种方式：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|686207|results+=+results.Where(o+=>+(o.OrderStatus+==+OrderStatus.Open)+&&
+++++++++++++++++++++++++++++(o.CustomerID+==+customerID));|code-block|syntax|javascript|686208|或者：|686209|results+=+results.Where(o+=>+(o.OrderStatus+==+OrderStatus.Open))
+++++++++++++++++.Where(o+=>+(o.CustomerID+==+customerID));|686210|我通常更喜欢后者。但是，有必要对SQL服务器进行性能分析，以检查查询的执行情况，并查看哪个查询对您的数据执行得更好(如果有任何不同的话)。|686211|关于链接.Where()方法的注意事项:您可以将您想要的所有LINQ方法链接在一起。像.Where()这样的方法实际上还不会对数据库执行。它们使用defer+execution，直到计算出实际的结果(例如使用.Count()或.ToList())。因此，当您将多个方法链接在一起时(对.Where()的更多调用，可能是.OrderBy()或类似的东西，等等)它们构建了一个叫做expression+tree的东西。这整个树是在对数据源进行评估时对其执行的。|offset|length|style|CODE|686212|entityMap|0|LINK|mutability|MUTABLE|url|http://blogs.msdn.com/b/charlie/archive/2007/12/09/deferred-execution.aspx|1|http://msdn.microsoft.com/en-us/library/bb397951.aspx^0|0|0|0|0|0|4|8|17|8|2W|8|35|9|3Y|8|4F|A|21|F|0|58|F|1|0^^$0|@$1|2|3|4|5|6|7|12|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|13|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|14|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|15|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|16|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|17|8|@$O|18|P|19|Q|R]|$O|1A|P|1B|Q|R]|$O|1C|P|1D|Q|R]|$O|1E|P|1F|Q|R]|$O|1G|P|1H|Q|R]|$O|1I|P|1J|Q|R]]|9|@$O|1K|P|1L|1|1M]|$O|1N|P|1O|1|1P]]|A|$]]|$1|S|3|-4|5|6|7|1Q|8|@]|9|@]|A|$]]]|T|$U|$5|V|W|X|A|$Y|Z]]|10|$5|V|W|X|A|$Y|11]]]]

Two ways:

<pre><code>results = results.Where(o =&gt; (o.OrderStatus == OrderStatus.Open) &amp;&amp;
 (o.CustomerID == customerID));
</code></pre>

or:

<pre><code>results = results.Where(o =&gt; (o.OrderStatus == OrderStatus.Open))
 .Where(o =&gt; (o.CustomerID == customerID));
</code></pre>

I usually prefer the latter. But it's worth profiling the SQL server to check the query execution and see which one performs better for your data (if there's any difference at all).

A note about chaining the <code>.Where()</code> methods: You can chain together all the LINQ methods you want. Methods like <code>.Where()</code> don't actually execute against the database (yet). They <a href="http://blogs.msdn.com/b/charlie/archive/2007/12/09/deferred-execution.aspx">defer execution</a> until the actual results are calculated (such as with a <code>.Count()</code> or a <code>.ToList()</code>). So, as you chain together multiple methods (more calls to <code>.Where()</code>, maybe an <code>.OrderBy()</code> or something to that effect, etc.) they build up what's called an <a href="http://msdn.microsoft.com/en-us/library/bb397951.aspx">expression tree</a>. This entire tree is what gets executed against the data source when the time comes to evaluate it.

blocks|key|470179|text|您可以使用&&并将所有条件写到同一个where子句中，也可以使用.Where()...诸若此类。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|470180|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|$]]

you can use &amp;&amp; and write all conditions in to the same where clause, or you can .Where().Where().Where()... and so on.

I have a LINQ query that looks like the following:

<pre><code>DateTime today = DateTime.UtcNow;
var results = from order in context.Orders
 where ((order.OrderDate &lt;= today) &amp;&amp; (today &lt;= order.OrderDate))
 select order;
</code></pre>

I am trying to learn / understand LINQ. In some cases, I need to add two additional WHERE clauses. In an effort to do this, I'm using:

<pre><code>if (useAdditionalClauses)
{
 results = results.Where(o =&gt; o.OrderStatus == OrderStatus.Open) // Now I'm stuck.
}
</code></pre>

As you can see, I know how to add an additional WHERE clause. But how do I add multiple? For instance, I'd like to add 

<code>WHERE o.OrderStatus == OrderStatus.Open AND o.CustomerID == customerID</code>

to my previous query. How do I do this using extension methods?

Thank you!

Multiple WHERE Clauses with LINQ extension methods

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我有一个LINQ查询，如下所示：DateTime today = DateTime.UtcNow;var results = from order in context.Orders where ((order.OrderDate <= today) && (today <= order.Or...

问具有LINQ扩展方法的多个WHERE子句
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