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POUsing the ODATA $expand query option with WebAPI and a ViewModel
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  1. POUsing the ODATA $expand query option with WebAPI and a ViewModel
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    copied!<p><a href="https://stackoverflow.com/questions/19323545/odata-expand-dtos-and-entity-framework">This question</a> is very similar but does not give me what I need.</p> <p>I am using Entity Framework 6. My database has two tables, Customers and CustomerTypes. I have created a ViewModel for each. A customer can have a type:</p> <pre><code>public class Customer { public int CustomerID { get; set; } public string CustomerName { get; set; } public CustomerTypeViewModel CustomerType { get; set; } } public class CustomerTypeViewModel { public int CustomerTypeID { get; set; } public string CustomerTypeDescription { get; set; } } </code></pre> <p>I have a Customer controller which exposes an odata action method with a return type of IQueryable:</p> <pre><code>[HttpPost, Queryable(AllowedQueryOptions = AllowedQueryOptions.All)] public IQueryable&lt;CustomerViewModel&gt; GetCustomersMatchingCriteria([FromBody]ODataActionParameters parameters) { var criteria = (CustomerMassUpdateCriteriaViewModel)parameters["Criteria"]; return Common.Customers.GetCustomerMassUpdateCriteriaResults(criteria, ConfigurationManager.AppSettings["CLIENT_ID"]).Select( c =&gt; new CustomerViewModel() { CustomerID = c.CustomerID, CustomerName = c.CustomerName, CustomerType = new CustomerTypeViewModel() { CustomerTypeDescription = c.CustomerType.CustomerTypeDescription } }); } </code></pre> <p>The Common.Customers.GetCustomerMassUpdateCriteriaResults method just returns an IQueryable of Customer, which is the actual entity.</p> <p>The problem is, when calling this controller method with the following query string options:</p> <pre><code>$expand=CustomerType $select=CustomerID,CustomerName,CustomerType/CustomerTypeDescription </code></pre> <p>This exception is thrown:</p> <p><em>The 'ObjectContent`1' type failed to serialize the response body for content type 'application/json; charset=utf-8'.","type":"System.InvalidOperationException"</em></p> <p><em>The argument to DbIsNullExpression must refer to a primitive, enumeration or reference type.</em></p> <p>Removing the $expand option and the associated CustomerType/CustomerTypeDescription property from the $select list produces no error.</p> <p>I feel like I'm missing something obvious, here. Any ideas?</p> <p><strong>1st EDIT:</strong></p> <p>Enumerating the results via the ToList() extension method and returning IEnumerable rather than IQueryable successfully expands the CustomerType navigation property, but my ODATA $select list is no longer respected at the database level. Doesn't that defeat the purpose of using ODATA?</p>
 

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