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POEntity Framework, Generic Repository Pattern and strange SQL generation
 

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    <p>I've implemented a generic repository for Entity Framework 4. Here's a dumbed down version, where AllAppContainer is the EF4 object context:</p> <pre><code>public class Repository&lt;T&gt; where T : class { protected AllAppContainer objectContext; protected ObjectSet&lt;T&gt; entitySet; public Repository() { objectContext = new AllAppContainer(); entitySet = objectContext.CreateObjectSet&lt;T&gt;(); } public int QueryCount(Func&lt;T, bool&gt; predicate) { int queryCount = entitySet.Count(predicate); return queryCount; } } </code></pre> <p>The one method is QueryCount(), which I want to act as a <strong>select Count(*) ... where</strong> line of SQL (not returning the actual records).</p> <p>Straight-forward? You'd think... First, let's do a non-Repository version of the same thing, performing a count on Item entities:</p> <pre><code>AllAppContainer allAppContainer = new AllAppContainer(); int nonRepCount = allAppContainer.Items.Count(item =&gt; item.Id &gt; 0); </code></pre> <p>SQL Server Profiler says the generated SQL is:</p> <pre><code>SELECT [GroupBy1].[A1] AS [C1] FROM ( SELECT COUNT(1) AS [A1] FROM [dbo].[Items] AS [Extent1] WHERE [Extent1].[Id] &gt; 0 ) AS [GroupBy1] </code></pre> <p>Woo-hoo! Score!</p> <p>Now let's call the same using my Repository QueryCount:</p> <pre><code>Repository&lt;Item&gt; repository = new Repository&lt;Item&gt;(); int repCount = repository.QueryCount(item =&gt; item.Id &gt; 0); </code></pre> <p>Here's the generated SQL:</p> <pre><code>SELECT [Extent1].[Id] AS [Id], [Extent1].[SmallField] AS [SmallField] FROM [dbo].[Items] AS [Extent1] </code></pre> <p>Yep, EF is returning the full set of data, then calling <em>Count()</em> on it in-memory.</p> <p>For fun I tried changing the relevant line in Repository QueryCount to:</p> <pre><code>int queryCount = new AllAppContainer().CreateObjectSet&lt;T&gt;().Count(predicate); </code></pre> <p>and the non-repository line to:</p> <pre><code>int nonRepCount = allAppContainer1.CreateObjectSet&lt;Item&gt;().Count(item =&gt; item.Id &gt; 0); </code></pre> <p>but the generated SQL for each is the same as before.</p> <p>Now why would all this repository-returns-all-matching-records-then-counts be happening, when it doesn't for non-repository? And is there any way to do what I want via my generic repository i.e. count at db. I can't take the in-memory count performance hit.</p>
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