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POWhy do I have to supply foreign key property values manually (in this situation)?
 

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  1. POWhy do I have to supply foreign key property values manually (in this situation)?
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    <p>When I have a model like this...</p> <pre><code>public class Order { [Key, Column(Order = 1)] public int CustomerId { get; set; } [Key, Column(Order = 2)] public int OrderId { get; set; } public ICollection&lt;OrderItem&gt; Items { get; set; } } public class OrderItem { [Key, Column(Order = 1)] public int CustomerId { get; set; } [Key, Column(Order = 2)] public int OrderId { get; set; } [Key, Column(Order = 3)] public int OrderItemId { get; set; } } </code></pre> <p>...I don't need to supply the foreign key values <code>OrderItem.CustomerId</code> and <code>OrderItem.OrderId</code> manually when I add an <code>Order - OrderItems</code> graph to the database:</p> <pre><code>var order = new Order { CustomerId = 5, OrderId = 1, Items = new List&lt;OrderItem&gt; { // I don't need to set CustomerId and OrderId here new OrderItem { OrderItemId = 12 } } }; context.Orders.Add(order); context.SaveChanges(); </code></pre> <p><code>SaveChanges</code> will generate SQL statements to insert the <code>Order</code> and the <code>OrderItem</code>. For <code>OrderItem</code> it is:</p> <pre><code>exec sp_executesql N'insert [dbo].[OrderItems]([CustomerId], [OrderId], [OrderItemId]) values (@0, @1, @2) ',N'@0 int,@1 int,@2 int',@0=5,@1=1,@2=12 </code></pre> <p>So, the FKs <code>CustomerId</code> and <code>OrderId</code> are correctly set (<code>@0=5</code> and <code>@1=1</code>).</p> <p>However, if I add another relationship to a <code>Customer</code> entity to the model by just adding a navigation property to <code>Order</code>...</p> <pre><code>public Customer Customer { get; set; } </code></pre> <p>...with a <code>Customer</code> class like this...</p> <pre><code>public class Customer { [DatabaseGenerated(DatabaseGeneratedOption.None)] public int CustomerId { get; set; } } </code></pre> <p>...and call the same code like above (assuming that a <code>Customer</code> with <code>CustomerId</code> = <code>5</code> exists in the DB) I get the following SQL:</p> <pre><code>exec sp_executesql N'insert [dbo].[OrderItems]([CustomerId], [OrderId], [OrderItemId]) values (@0, @1, @2) ',N'@0 int,@1 int,@2 int',@0=0,@1=1,@2=12 </code></pre> <p>Almost the same, but the <code>CustomerId</code> is <code>0</code> in this case (<code>@0=0</code>) which results in a foreign key constraint violation for the <code>Order - OrderItem</code> relationship. If a <code>Customer</code> with <code>CustomerId</code> = <code>0</code> would exist and this customer had an <code>Order</code> with <code>OrderId</code> = <code>1</code>, no exception would occur and the <code>OrderItem</code> would have been added to a wrong order which might be worse than an exception.</p> <p>The problem can be fixed by setting the <code>CustomerId</code> (which is part of the FK) in the new <code>OrderItem</code>:</p> <pre><code>Items = new List&lt;OrderItem&gt; { // I don't need to set OrderId here, BUT CustomerId new OrderItem { CustomerId = 5, OrderItemId = 12 } } </code></pre> <p>Or - it can be fixed by attaching the customer with Id <code>5</code> to the context (I have no clue why it works then).</p> <p><strong>Is there a reasonable explanation why I have to supply the FK (or part of the FK in this example) manually or is this a bug?</strong></p> <p>(I have used EF 5.0 with .NET 4.0 for this model.)</p>
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    1. USSlauma
    1. USSlauma
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      1. POWhy do I have to supply foreign key property values manually (in this situation)?
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      1. VTUpMod
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      1. POWhy do I have to supply foreign key property values manually (in this situation)?
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      1. VTUpMod
    1. COThat's pretty weird, I can understand why you would need to set CustomerId it for a *new* customer but it doesn't make a lot of sense that this would change the behavior of how FKs are auto-assigned based on nav properties
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      1. POWhy do I have to supply foreign key property values manually (in this situation)?
      1. USLuke McGregor
    2. COIs there any difference between the generated FK in the database ? this may help http://msdn.microsoft.com/en-us/data/jj591583#relationships
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      1. POWhy do I have to supply foreign key property values manually (in this situation)?
      1. USknaki02
    3. CO@knaki02: No, the FK from `OrderItem` to `Order` is the same (composite FK with (`CustomerId`,`OrderId`)). Only `CustomerId` will become a second FK from `Order` to `Customer`. The database schema is correct and as expected in both cases.
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      1. POWhy do I have to supply foreign key property values manually (in this situation)?
      1. USSlauma
 

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