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POEntity Framework - casting property on null object doesn't throw an exception?
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  1. POEntity Framework - casting property on null object doesn't throw an exception?
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    copied!<p>I'm reviewing some legacy code and came across a snippet which seems like it will throw unwanted exceptions. In essence the code (an EntityFramework query) looks like the following:</p> <pre><code>var serviceId = (Guid?) person.Services.FirstOrDefault(s =&gt; s.Name == "foo").Id; bool inService = serviceId.HasValue; </code></pre> <p>That is, a <code>person</code> has multiple services assigned to them, and we're returning the first service whose <code>Name</code> is <code>foo</code>. Then, we get the Id property (a Guid) on that <code>Service</code> instance, and cast it to a nullable Guid. Finally, if that nullable Guid has a value, then the person must be in that service.</p> <p>(Note: this is not how I would choose to write the above, it's just what I'm working with)</p> <p>I have a feeling that this code simply throws exceptions when the person does not belong to a service with the name "foo" (or really, any service at all), because the <code>FirstOrDefault</code> invocation will return a <code>null</code> <code>Service</code> instance, and accessing the <code>Id</code> property will just throw an NPE.</p> <p>I asked the original developer about this snippet, and I was told that doing the following:</p> <pre><code>(T?) entity.&lt;non-existent entity&gt;.SomeProperty </code></pre> <p>Will simply return a null object, instead of throwing an NPE. Also, this type of "safe null handling" occurs with Entity Framework queries.</p> <p>This seems incredibly counter-intuitive, and doesn't even feel like it should be possible. I tried researching this, but I haven't found anything along those lines. Does anyone have any experience with this? I'm 100% happy to find out that I'm wrong and to learn something new, but it does not feel correct to me.</p> <p><em>As an addendum, I did try running the query above in Linqpad by using the EntityFramework connection, and I did indeed generate an NPE when trying to access the null objects property</em> </p>
 

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