title: simple linq to sql has no supported translation to SQL
body: <p>i have this in my BlogRepository</p>
  
  <pre><code>public IQueryable&lt;Subnus.MVC.Data.Model.Post&gt; GetPosts()
      {
          var query = from p in db.Posts
                      let categories = GetCategoriesByPostId(p.PostId)
                      let comments = GetCommentsByPostId(p.PostId)
                      select new Subnus.MVC.Data.Model.Post
                      {
                          Categories = new LazyList&lt;Category&gt;(categories),
                          Comments = new LazyList&lt;Comment&gt;(comments),
                          PostId = p.PostId,
                          Slug = p.Slug,
                          Title = p.Title,
                          CreatedBy = p.CreatedBy,
                          CreatedOn = p.CreatedOn,
                          Body = p.Body
                      };
          return query;
      }
  </code></pre>
  
  <p>and </p>
  
  <pre><code>public IQueryable&lt;Subnus.MVC.Data.Model.Comment&gt; GetCommentsByPostId(int postId)
      {
          var query = from c in db.Comments
                      where c.PostId == postId
                      select new Subnus.MVC.Data.Model.Comment
                      {
                          Body = c.Body,
                          EMail = c.EMail,
                          Date = c.CreatedOn,
                          WebSite = c.Website,
                          Name = c.Name
                      };
  
          return query;
      }
  
  private IQueryable&lt;Subnus.MVC.Data.Model.Category&gt; GetCategoriesByPostId(int postId)
      {
          var query = from c in db.Categories
                      join pcm in db.Post_Category_Maps on c.CategoryId equals pcm.CategoryId
                      where pcm.PostId == postId
                      select new Subnus.MVC.Data.Model.Category
                      {
                          CategoryId = c.CategoryId,
                          Name = c.Name
                      };
          return query;
      }
  </code></pre>
  
  <p>and when i aplly this filter  </p>
  
  <pre><code>namespace Subnus.MVC.Data
  {
   public static class BlogFilters
   {
      public static IQueryable&lt;Post&gt; WherePublicIs(this IQueryable&lt;Post&gt; qry,bool state)
      {
  
          return from p in qry
                 where p.IsPublic == state
                 select p;
      }
   }
  </code></pre>
  
  <p>}</p>
  
  <p>all this is in the same namespace if that help namespace Subnus.MVC.Data</p>
  
  <p>when i try to do this  </p>
  
  <pre><code>public class BlogService : IBlogService
  {
  ...
      public IList&lt;Post&gt; GetPublicPosts()
      {
           return repository.GetPosts().WherePublicIs(true).ToList();
      }
   ...
   }
  </code></pre>
  
  <p>that is in the namespace Subnus.MVC.Service
  it throws the error  </p>
  
  <pre><code>Method 'System.Linq.IQueryable`1[Subnus.MVC.Data.Model.Comment] GetCommentsByPostId(Int32)' has no supported translation to SQL.
  </code></pre>