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POLinq to entities: new Guid("") for anonymous type creation vs select
 

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    <p>Following my previous question (<a href="https://stackoverflow.com/questions/16146930/only-parameterless-constructors-and-initializers-are-supported-in-linq-to-entiti/16146972?noredirect=1#comment23072925_16146972">Only parameterless constructors and initializers are supported in LINQ to Entities</a>) I'm still having a question. I just want to understand what is going on and why something works in one case and not another.</p> <p>When you want to cast a string parameter (for example a querystring parameter) in a Linq to entities query, you have to use new Guid(request.querystring("param")) instead of Guid.parse(request.querystring("param")). Guid.parse will throw an exception because Linq cannot translate this into SQL.</p> <p>I'm using this technique often in my code and it works.</p> <pre><code>dim lstResult = DB.MyTable.Where(function(f) f.key = new Guid(request.querystring("param"))).toList() </code></pre> <p>But, when I'm trying to create an anonymous type using a Linq query, it will throw an exception:</p> <pre><code>dim lstResult = DB.MyTable.Where(function(f) f.key = new Guid(request.querystring("param"))).Select(function(f) new With { .guid = f.guid, .name = f.name }).toList() </code></pre> <p>The thrown exception is:</p> <blockquote> <p>Only parameterless constructors and initializers are supported in LINQ to Entities</p> </blockquote> <p>What I could (or should) do is declare the Guid parameter beforehand (and that is maybe good practice) and than using it in the query. It will work:</p> <pre><code>dim myGuid = Guid.parse(request.querystring("param")) dim lstResult = DB.MyTable.Where(function(f) f.key = myGuid).Select(function(f) new With { .guid = f.guid, .name = f.name }).toList() </code></pre> <p>So, my question is: why would it work without creating anonymous types and why is the exception raised when trying to create anonymous types? What is the mechanism causing this exception?</p>
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    1. COHave you verified that only the anonymous type select causes this? What about simply selecting f.guid, or using a second Where, etc?
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