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POCheck if value is null, and when it is, execute extra (sub)query
 

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    <p>Is it possible to check for a null value in a LINQ query and when the value is null, that it executes an extra (sub)query, all at once?</p> <p><strong>Explanation</strong></p> <p>I have default buttons declared in my database, with default <em>descriptions</em>. A user can customize these buttons, and these settings are stored in the <code>ButtonLocations</code> table. Now, every button has a standard description and the user can edit this description. When the user edits the description, it is stored in the <code>Descriptions</code> table in my database. When I retrieve all buttons, I first check if a button has a specific description (in <em>buttonlocations</em>, with a left join). If this is not true (so null), I retrieve the default description. </p> <p>Currently I get all my entities with their description and after that I loop through all of them to check if the value is null. This results in multiple queries to the database.</p> <pre><code>var temp = (from bl in context.buttonLocations join b in context.Buttons on bl.ButtonID equals b.ButtonID into buttons from button in buttons.DefaultIfEmpty() join d in context.Descriptions on new { ID = bl.ButtonLocationID, langID = languageID, originID = descriptionOriginID } equals new { ID = d.ValueID, langID = d.LanguageID, originID = d.DescriptionOriginID } into other where bl.ButtonGroupID == buttonGroupId from x in other.DefaultIfEmpty() select new { Button = button, ButtonLocation = bl, Description = x }).ToList(); // Retrieve default descriptions if no specific one is set foreach (var item in temp) { if (item.Description == null) { item.Description = context.Descriptions .FirstOrDefault(x =&gt; x.ValueID == item.Button.ButtonID &amp;&amp; x.LanguageID == languageID &amp;&amp; x.DescriptionOriginID == (short)DescriptionOriginEnum.Button); } } </code></pre>
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