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POEntity Framework - How to load empty children
 

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  1. POEntity Framework - How to load empty children
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    <p>Am getting started using Entity Framework and have run into a problem.</p> <p>Say I have 2 tables in my database. One called Agent that contains an ID and a password and another table called AgentDetail that contains more information about the Agent. However, there might not be a corresponding AgentDetail record for every Agent record.</p> <p>I have these 2 classes to represent those 2 tables:</p> <pre><code>public class Agent { public string AgentId { get; set; } public string Password { get; set; } public virtual AgentDetail AgentDetail { get; set; } } public class AgentDetail { public string AgentDetailId { get; set; } public string AgentName { get; set; } public string Postcode { get; set; } } </code></pre> <p>Using EF I can add data to the database OK. I can also retrieve data OK when there is a corresponding record in both tables.</p> <pre><code> var agents = from a in context.Agents select a; return View(agents.ToList()); </code></pre> <p>However I get a NullReferenceException in my view when rendering values within AgentDetail if that record doesn't exist in the AgentDetail table.</p> <p>Now that's totally expected as there is no AgentDetail record.</p> <p>My question is how do I get EF to create an AgentDetail with empty values when the record doesn't exist in the table.</p> <p>Can I add an empty child object in the LINQ query - something like:</p> <pre><code> var agents = (from a in rb.Agents select new { AgentId = a.AgentId, Password = a.Password, AgentDetail = a.AgentDetail == null ? new AgentDetail() : a.AgentDetail, }).ToList(); </code></pre> <p>(the above doesn't work however as I get the following message:</p> <p>The entity or complex type 'Models.AgentDetail' cannot be constructed in a LINQ to Entities query.)</p>
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    1. This table or related slice is empty.
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    1. USBrightonDev
    1. USBrightonDev
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    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
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    1. This table or related slice is empty.
    1. COAre you wanting EF to actually create the AgentDetail if one doesn't exist, record so one will be persisted in the database?
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      1. POEntity Framework - How to load empty children
      1. USMark Oreta
    2. COHi Mark, No I'm not bothered about that. I just wanted to know the best way to handle child data that doesnt exist
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      1. POEntity Framework - How to load empty children
      1. USBrightonDev
 

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