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POFastest, cleanest way in linq to exclude elements from other type (+ef)
 

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  1. POFastest, cleanest way in linq to exclude elements from other type (+ef)
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    <p>Assume we have these two classes:</p> <pre><code>class GenericFoo { public Guid ID; ... } class SpecialFoo { public Guid ID; public Guid GenericFooID; ... } </code></pre> <p>GenericFoo is a kind of template class, that SpecialFoos can be created from. </p> <p>Now, I have a <code>DbSet&lt;GenericFoo&gt; g</code> and a <code>DbSet&lt;SpecialFoo&gt; s</code>. Any SpecialFoo.GenericFooID <em>may</em> exist in g, but may also be missing. (The GenericFoo may e.g. have been deleted). The opposite is true as well, of course.</p> <p>What I would like is a call to get the ones that lacks matching GenericFooID, something like:</p> <pre><code>missing = s.Except(g) </code></pre> <p>That doesn't work, since Except only works for same classes. For now I've solved this by using a rather contrived solution:</p> <pre><code>ExistingIds = g.Select(f=&gt;f.ID); missing = s.Where(f =&gt; !ExistingIds.Contains(s.GenericFooID)); </code></pre> <p>One major downside here is that we lose type safety (if someone mistype g and specifies a similar class, there would be no way to check this). I would prefer having something like an <code>IComparer&lt;type1, type2&gt;</code> so that the <code>Except</code> call would work.</p> <p>The other options I've found is </p> <ul> <li>to make a "fake left join" using group join, and just keeping the non matching</li> <li>to convert the first one into a dictionary, hash table etc. just to speed it up</li> <li>attempting to create a Generic->Special converter, and then a IComparer just for the sake of using <code>Except</code></li> </ul> <p>My questions are:</p> <ol> <li>Are there any nicer way to solve this, just talking about linq to objects?</li> <li>What is the fastest way to solve this, in the context of entity framework?</li> </ol>
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    1. USNiklasJ
    1. USNiklasJ
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    1. COSo what, is it LINQ2Objects or EF?
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      1. USIt'sNotALie.
    2. COWell, does it make that much of a difference? L2O for question 1, EF for question 2.
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      1. USNiklasJ
    3. COThen why do you have a DBSet? Also, L2O opens up stuff like MoreLINQ.
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      1. USIt'sNotALie.
 

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