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POLinq to Entities excessive joins in generated SQL
 

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  1. POLinq to Entities excessive joins in generated SQL
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    <p>I have a .NET Entity Data Model set up with relationships so that I don't need to manually join entities in my LINQ queries. The LINQ query below references another table <strong>CustomerUserField</strong>:</p> <pre><code>from c in Customer.GetCustomer(this.ClientId, intRecordId) select new { c.TitleId, c.FirstName, c.LastName, c.Phone, c.MobilePhone, c.Fax, c.EmailAddress, c.CustomerUserField.Text1, c.CustomerUserField.Text2, c.CustomerUserField.Text3, c.CustomerUserField.Text4, c.CustomerUserField.Text5 }; </code></pre> <p>It looks nice &amp; neat in C#, however the generated SQL creates a separate left outer join for every column in the referenced table:</p> <pre><code>SELECT [Limit1].[C1] AS [C1], [Limit1].[TitleId] AS [TitleId], ... FROM [dbo].[Customer] AS [Extent1] LEFT OUTER JOIN [dbo].[CustomerUserField] AS [Extent2] ON [Extent1].[CustomerId] = [Extent2].[CustomerId] LEFT OUTER JOIN [dbo].[CustomerUserField] AS [Extent9] ON [Extent2].[CustomerUserFieldId] = [Extent9].[CustomerUserFieldId] LEFT OUTER JOIN [dbo].[CustomerUserField] AS [Extent10] ON [Extent2].[CustomerUserFieldId] = [Extent10].[CustomerUserFieldId] LEFT OUTER JOIN [dbo].[CustomerUserField] AS [Extent11] ON [Extent2].[CustomerUserFieldId] = [Extent11].[CustomerUserFieldId] LEFT OUTER JOIN [dbo].[CustomerUserField] AS [Extent12] ON [Extent2].[CustomerUserFieldId] = [Extent12].[CustomerUserFieldId] LEFT OUTER JOIN [dbo].[CustomerUserField] AS [Extent13] ON [Extent2].[CustomerUserFieldId] = [Extent13].[CustomerUserFieldId]... </code></pre> <p>This SQL is very slow, as only 1 left outer join is required. Any ideas how I can change my LINQ to only perform a single join?</p> <p>Thanks in advance!</p> <p>Anthony.</p>
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      1. USJon Limjap
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    1. COI'd check the execution plan before saying this is bad. The plan compilation might understand and only query the CustomerUserField once. Not 100% sure but I've seen things queries like this actually optimize pretty well.
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      1. USjfar
    2. COIt is bad, at least on SQL Server 2008 R2 and earlier. SQL Server will not optimize those excess joins away.
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      1. POLinq to Entities excessive joins in generated SQL
      1. USPeter Radocchia
 

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