blocks|key|489656|text|您可以在基类型上有一个方法，该方法在派生类型中被重写，以提供相关的属性值。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|489657|public+class+MyBaseClass
{
++++public+virtual+int+GetSomething()
++++{
++++++++throw+new+NotImplementedException();
++++}
}

public+class+MyDerivedClass1+:+MyBaseClass
{
++++public+int+SomeProperty+{+get;+set;+}

++++public+override+int+GetSomething()
++++{
++++++++return+this.SomeProperty;
++++}
}

public+class+MyDerivedClass2+:+MyBaseClass
{
++++public+int+SomeOtherProperty+{+get;+set;+}

++++public+override+int+GetSomething()
++++{
++++++++return+this.SomeOtherProperty;
++++}
}|code-block|syntax|javascript|489658|然后，您可以：|489659|var+result+=+base.Select(b+=>+b.GetSomething()).ToList();|489660|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|$]]

You could have a method on your base type that's overridden in your derived types to provide the relevant property value.

<pre><code>public class MyBaseClass
{
 public virtual int GetSomething()
 {
 throw new NotImplementedException();
 }
}

public class MyDerivedClass1 : MyBaseClass
{
 public int SomeProperty { get; set; }

 public override int GetSomething()
 {
 return this.SomeProperty;
 }
}

public class MyDerivedClass2 : MyBaseClass
{
 public int SomeOtherProperty { get; set; }

 public override int GetSomething()
 {
 return this.SomeOtherProperty;
 }
}
</code></pre>

Then you could:

<pre><code>var result = base.Select(b =&gt; b.GetSomething()).ToList();
</code></pre>

blocks|key|272639|text|试试这个，我从来没有做过任何需要这样做的事情，但是这个应该可以做到。另外，如果你使用base，首先不要使用它，因为它是一个关键字，但如果你必须使用@base，在名称前面的@表示它不被用作关键字。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|272640|var+resultA+=+base.Select(aVar+=>
++++++++++++++++++++++++++++(aVar+is+DerivedType1)+?
++++++++++++++++++++++++++++++++(DerivedType)(((DerivedType1)aVar).DerivedProperty)
++++++++++++++++++++++++++++++++:
++++++++++++++++++++++++++++++++(DerivedType)(default(int?))
++++++++++++++++++++++++).ToList();|code-block|syntax|javascript|272641|entityMap^0|16|4|21|5|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]|$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|S|8|@]|D|@]|E|$]]]|L|$]]

Try this, I have never done anything with needing to do this kind of this but this should do it. Also if you use <code>base</code>, first of all don't because it is a keyword but if you must, use <code>@base</code> the @ in front of the name denotes that it is not used as a keyword.

<pre><code>var resultA = base.Select(aVar =&gt;
 (aVar is DerivedType1) ?
 (DerivedType)(((DerivedType1)aVar).DerivedProperty)
 :
 (DerivedType)(default(int?))
 ).ToList();
</code></pre>

blocks|key|489795|text|OfType<DerivedType1>()+|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|489796|将返回一个IEnumerable，如果可能的话，尝试将基本类型更改为IEnumerable而不是IQueryable，在使用IQueryable时可能会增加一些SQL限制。|unstyled|489797|当然，如果你实际上不是在查询数据库的话？|489798|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|L|8|@]|9|@]|A|$]]|$1|G|3|H|5|F|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|F|7|N|8|@]|9|@]|A|$]]]|J|$]]

<pre><code>OfType&lt;DerivedType1&gt;() 
</code></pre>

will return an IEnumerable, if possible, try to change to base-type to IEnumerable instead of IQueryable, you might en up in some SQL restrictions when using IQueryable.

That is of course if you are not actually quering a database?

blocks|key|489842|text|LINQ-+to+-Entities不支持直接转换为像(DerivedType1)b这样的实体类型，但是as运算符(b+as+DerivedType1)支持，因此您可以尝试：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|489843|var+result2+=+base
++++.Select(b+=>+b+is+DerivedType1
++++++++?+(b+as+DerivedType1).DerivedProperty
++++++++:+null)
++++.ToList();|code-block|syntax|javascript|489844|entityMap^0|R|F|1G|2|1M|H|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|$]]

Direct casting to an entity type like <code>(DerivedType1)b</code> isn't supported with LINQ-to-Entities but the <code>as</code> operator (<code>b as DerivedType1</code>) is, hence you could try:

<pre><code>var result2 = base
 .Select(b =&gt; b is DerivedType1
 ? (b as DerivedType1).DerivedProperty
 : null)
 .ToList();
</code></pre>

blocks|key|272816|text|您可以使用EntityFramework.Extended来提高查询的性能，而不是与数据库进行两次往返。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|272817|var+resultA+=+base.OfType<DerivedType1>().Select(d+=>+d.DerivedProperty).Future();
var+resultB+=+base.OfType<DerivedType2>().Select(d+=>+default(int?)).Future();
var+result+=+resultA.Concat(resultB).ToList();|code-block|syntax|javascript|272818|在这种情况下，只执行一次到bd的往返。这个框架对其他很多事情都非常有用。|272819|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 use EntityFramework.Extended to improve the performance of the query instead of doing 2 round trips to DB.

<pre><code>var resultA = base.OfType&lt;DerivedType1&gt;().Select(d =&gt; d.DerivedProperty).Future();
var resultB = base.OfType&lt;DerivedType2&gt;().Select(d =&gt; default(int?)).Future();
var result = resultA.Concat(resultB).ToList();
</code></pre>

In this case only one round trip to bd is executed.
This framework is very useful for many other things int EF

I have a LINQ to entities model with Table Per Hierarchy inheritance. I have a query over the base type, and I want to do specific type-dependent logic. For example:

<pre><code>IQueryable&lt;BaseType&gt; base = ...

// this works fine
var result = base.Select(b =&gt; b is DerivedType1 ? 1 : 2).ToList();

// this doesn't compile to SQL
var result2 = base.Select(b =&gt; b is DerivedType1 ? ((DerivedType1)b).DerivedProperty : null).ToList();
</code></pre>

Is there any way to do something like this without processing IQueryables of each derived type separately:

<pre><code>// I'd rather not do this:
var resultA = base.OfType&lt;DerivedType1&gt;().Select(d =&gt; d.DerivedProperty);
var resultB = base.OfType&lt;DerivedType2&gt;().Select(d =&gt; default(int?));
var result = resultA.Concat(resultB).ToList();
</code></pre>

Casting to a derived type in a LINQ to Entities query with Table Per Hierarchy inheritance

数据库

我有一个LINQ到实体模型与表每个层次结构继承。我有一个基类型的查询，我想做一个特定的依赖于类型的逻辑。例如：IQueryable<BaseType> base = ...// this works finevar result = base.Select(b => b is DerivedType1 ? 1 : 2)...

问在具有每个层次结构的表继承的LINQ to Entities查询中强制转换为派生类型
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