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POProblem with Eager Loading Nested Navigation Based on Abstract Entity (EF CTP5)
 

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  1. POProblem with Eager Loading Nested Navigation Based on Abstract Entity (EF CTP5)
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    <p>I a portion of my EF model that looks like this:</p> <p><img src="https://i.stack.imgur.com/XGvyH.png" alt="enter image description here"></p> <p>Summary:</p> <ul> <li>Location has <strong>many</strong> Posts</li> <li>Post is an <strong>abstract</strong> class</li> <li>Discussion <strong>derives</strong> from <strong>Post</strong></li> <li>Discussions have <strong>many</strong> Comments</li> </ul> <p>Now, the query i'm trying to achieve:</p> <p><strong>Get information about Location Id 1234, including any Discussions and Comments associated with those Discussions.</strong></p> <p>I can get discussions and the comments like this:</p> <pre><code>var discussions = ctx.Posts .OfType&lt;Discussion&gt;() .Include(x =&gt; x.Comments) .ToList(); </code></pre> <p>But i can't seem to get it based on the <strong>Posts</strong> navigation on the <strong>Location</strong> entity.</p> <p>I've tried this:</p> <pre><code>var locationWithDiscussionsAndComments = ctx .Locations .Include(x =&gt; x.Posts .OfType&lt;Discussion&gt;() .Select(y =&gt; y.Comments)) .SingleOrDefault(); </code></pre> <p>Which compiles, but i get the error:</p> <blockquote> <p>System.ArgumentException: The include path expression must refer to a property defined by the entity, optionally also with nested properties or calls to Select. Parameter name: path</p> </blockquote> <p>Any ideas? I could probably go "backwards" from the Posts:</p> <pre><code>var locationWithDiscussionsAndComments = ctx .Posts .Include(x =&gt; x.Location) .OfType&lt;Discussion&gt;() .Include(x =&gt; x.Comments) .Where(x =&gt; x.LocationId == 1234) .Select(x =&gt; x.Location) .ToList(); </code></pre> <p>But that is both hairy and semantically wrong in terms of my repositories (i shouldn't have to go through a post repository to get information about a location).</p> <p>Any ideas?</p> <p><strong>EDIT</strong></p> <p>So after having a bigger think about it, i realized that <code>OfType&lt;T&gt;</code> is a filter operation. As as we know, EF does not support filtering with eager loading. The only options are retrieving <strong>everything</strong>, or using anonymous type projection.</p> <p>No way i can retrieve everything, as there is far too much meta data involved. So i'm attempting the anonymous type projection.</p>
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    1. COYes, after all the Lambda expression in the new *Include* overload is merely a property selector and you can't have any sort of filtering logic in it. Like you mentioned, your best bet is to use anonymous projections here. Are you using DbContext here?
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    2. CO@Morteza - yes, im using `DbContext`, behind a `Repository<T>`, where `T` is an aggregate root, which `Location` and `Post` both are. So seperate repositories.
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    3. COOk, then you can use the new *Query* method to apply filters when explicitly loading related entities (it's not eager loading though) as explained here: http://blogs.msdn.com/b/adonet/archive/2011/01/31/using-dbcontext-in-ef-feature-ctp5-part-6-loading-related-entities.aspx
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