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POAggregating multiple queries into one with EF like this?
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  1. POAggregating multiple queries into one with EF like this?
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    copied!<p>I am using EF 4.0 POCO in my application. <strong>Are there any downsides to retrieving information like this?</strong></p> <p>Given a <code>customerId</code> and a <code>productId</code>, I would like to apply some business rules that require me to fetch lots teeny pieces of information from the database requiring multiple queries. Instead, I could write one query like so:</p> <pre><code>var customerId = 1; var productId = 1; var aggregateQuery = from entry in Customers.Take(0).DefaultIfEmpty() select new { numberOfOrders = SalesOrderHeaders.Where (header =&gt; header.CustomerID == customerId).Count(), canSellProduct = Products.Where(product =&gt; product.ProductID == productId &amp;&amp; product.SellEndDate &gt; DateTime.Now).Count () &gt; 0 //more infromation of this sort, required to enforce business rules }; var informationPacket = aggregateQuery.First(); </code></pre> <p>The <code>Customers.Take(0).DefaultIfEmpty()</code> just gives a way to start the query and <code>Customers</code>, <code>SalesOrderHeaders</code> and <code>Products</code> are EF ObjectQuery instances from the context (This example if from LinqPad). This results in the following SQL:</p> <pre><code>-- Region Parameters DECLARE @p0 Int = 1 DECLARE @p1 Int = 1 DECLARE @p2 DateTime = '2012-04-04 21:02:20.798' DECLARE @p3 Int = 0 -- EndRegion SELECT TOP (1) [t6].[value] AS [numberOfOrders], [t6].[value2] AS [canSellProduct] FROM ( SELECT ( SELECT COUNT(*) FROM [Sales].[SalesOrderHeader] AS [t3] WHERE [t3].[CustomerID] = @p0 ) AS [value], (CASE WHEN (( SELECT COUNT(*) FROM [Production].[Product] AS [t5] WHERE ([t5].[ProductID] = @p1) AND ([t5].[SellEndDate] &gt; @p2) )) &gt; @p3 THEN 1 WHEN NOT ((( SELECT COUNT(*) FROM [Production].[Product] AS [t5] WHERE ([t5].[ProductID] = @p1) AND ([t5].[SellEndDate] &gt; @p2) )) &gt; @p3) THEN 0 ELSE NULL END) AS [value2] FROM ( SELECT NULL AS [EMPTY] ) AS [t0] OUTER APPLY ( SELECT TOP (0) NULL AS [EMPTY] FROM [Sales].[Customer] AS [t1] ) AS [t2] ) AS [t6] </code></pre>
 

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