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POHandling dependent entities when deleting the principal with Entity Framework 5
 

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  1. POHandling dependent entities when deleting the principal with Entity Framework 5
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    <p>Here's the situation in its most simplified form using the EF5 Code-First approach:</p> <pre><code>public abstract class EntityBase&lt;PK&gt; { public PK ID { get; set; } } public class Country : EntityBase&lt;string&gt; { public string Name { get; set; } } public class Address : EntityBase&lt;int&gt; { [Required] public string CountryID { get; set; } public Country Country { get; set; } // ... other address properties ... } </code></pre> <p>The one-to-many relationship between <code>Address</code> and <code>Country</code> is set up with no cascade-delete like so:</p> <pre><code>modelBuilder.Entity&lt;Address&gt;() .HasRequired(a =&gt; a.Country) .WithMany() .HasForeignKey(a =&gt; a.CountryID) .WillCascadeOnDelete(false); </code></pre> <p>Finally, I have a generic base repository class with CRUD methods that call <code>SaveChanges</code> on the underlying DbContext to commit data changes atomically. E.g.:</p> <pre><code>public class EFRepository&lt;T, PK&gt; : IRepository&lt;T, PK&gt; where T : EntityBase&lt;PK&gt; { // // ... other methods ... // public virtual void Delete(T instance) { // ... trigger validations, write to log, etc... _dbContext.Set&lt;T&gt;().Remove(instance); try { _dbContext.SaveChanges(); } catch(Exception ex) { // ... handle the error ... } } } </code></pre> <p><strong>Part 1:</strong></p> <p>Scenario:</p> <pre><code>var countryRepo = new EFRepository&lt;Country&gt;(); var country = countryRepo.Save(new Country() { ID="??", Name="Test Country" }); var addressRepo = new EFRepository&lt;Address&gt;(); var address = addressRepo.Save(new Address() { Country=country }); countryRepo.Delete(country); </code></pre> <p>This should fail due to the existence of a dependent <code>Address</code>. However, afterwards the address ends up with a null in <code>CountryID</code>, which is invalid because <code>Address.CountryID</code> is required, so subsequent <code>SaveChanges</code> calls throw a validation exception unless the address is detached.</p> <p>I expected that when an object is deleted, EF5 will be smart enough to first check for any cascade-delete constraints like the one above and, failing to find any, then proceed to delete the data. But exactly the opposite seems to be the case.</p> <p>Is this a normal behaviour or am I doing something wrong?</p> <p><strong>Part 2:</strong></p> <p>Following a failed <code>SaveChanges</code> call, some <code>Addresses</code> are now in an invalid state in my DbContext and need to be restored to their original values. Of course, I can always do so explicitly for each entity type (<code>Country</code>, <code>State</code>, <code>Order</code>, etc.) by creating specialized repository classes and overriding <code>Delete</code>, but it smells big time. I'd much rather write some general purpose code to gracefully recover related entities after a failed <code>SaveChanges</code> call.</p> <p>It would require interrogating DbContext to get all relationships in which an entity (e.g. <code>Country</code>) is the principal, regardless of whether or not its class defines navigational properties to dependent entities. </p> <p>E.g. <code>Country</code> has no <code>Addresses</code> property, so I need to somehow find in DbContext the definition of the one-to-many relationship between <code>Country</code> and <code>Address</code> and use it to restore all related <code>Addresses</code> to their original values. </p> <p>Is this possible?</p>
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