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POEF 4.1 Code First - duplicate entities in object graph causes exception
 

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    <p>I am getting the following exception when attempting to save my entity:</p> <p><em>"AcceptChanges cannot continue because the object's key values conflict with another object in the ObjectStateManager. Make sure that the key values are unique before calling AcceptChanges."</em></p> <p>I'm creating a 3 tiered application where the data access layer is using EF Code First, and where the client calls the middle tier using WCF. I am therefore unable able to let the context track the entity state when building up an entity on the client.</p> <p>In some situations I am finding that the same entity is contained twice in the object graph. In this situation it fails when I try and set the entity state of the duplicate.</p> <p>For example, I have the following entities: Customer Country Curreny</p> <ol> <li>From the client I create a new instance of a Customer. I then make a service call to get Country instance and assign it to the Customer. The Country instance has an associated Currency.</li> <li>The user can then associate a Currency with the customer. They may well choose the same Currency that's associated with the Country.</li> <li>I make another service call to get this. Thus at this stage we may have two separate instances of the same currency.</li> </ol> <p>So what I end up with are two instance of the same entity in the object graph.</p> <p>When then saving the entity (in my service) I need to tell EF that both Currency entities are not modified (if I don't do this I get duplicates). Problem is that I get the exception above.</p> <p>On saving if I set the Currency instance on Country instance to null, it resolves the problem, but I feel like the code is becoming increasingly messy (due to this and other WCF related EF workarounds I'm having to put in place).</p> <p>Are there any suggestions on how to resolve this in a nicer way?</p> <p>Many thanks for any help in advance. Here's the code:</p> <pre><code>using System; using System.Collections.Generic; using System.Data.Entity.ModelConfiguration; using System.ComponentModel.DataAnnotations; using System.Data.Entity; using System.Linq; namespace OneToManyWithDefault { public class Customer { public int Id { get; set; } public string Name { get; set; } public Country Country { get; set; } public Currency Currency { get; set; } public byte[] TimeStamp { get; set; } } public class Country { public int Id { get; set; } public string Name { get; set; } public Currency Currency { get; set; } public byte[] TimeStamp { get; set; } } public class Currency { public int Id { get; set; } public string Symbol { get; set; } public byte[] TimeStamp { get; set; } } public class MyContext : DbContext { public DbSet&lt;Customer&gt; Customers { get; set; } public DbSet&lt;Currency&gt; Currency { get; set; } public DbSet&lt;Country&gt; Country { get; set; } public MyContext(string connectionString) : base(connectionString) { Configuration.LazyLoadingEnabled = false; Configuration.ProxyCreationEnabled = false; } protected override void OnModelCreating(DbModelBuilder modelBuilder) { modelBuilder.Configurations.Add(new CustomerConfiguration()); modelBuilder.Configurations.Add(new CountryConfiguration()); modelBuilder.Configurations.Add(new CurrencyConfiguration()); base.OnModelCreating(modelBuilder); } } public class CustomerConfiguration : EntityTypeConfiguration&lt;Customer&gt; { public CustomerConfiguration() : base() { HasKey(p =&gt; p.Id); Property(p =&gt; p.Id) .HasColumnName("Id") .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity) .IsRequired(); Property(p =&gt; p.TimeStamp) .HasColumnName("TimeStamp") .IsRowVersion(); ToTable("Customers"); } } public class CountryConfiguration : EntityTypeConfiguration&lt;Country&gt; { public CountryConfiguration() : base() { HasKey(p =&gt; p.Id); Property(p =&gt; p.Id) .HasColumnName("Id") .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity) .IsRequired(); Property(p =&gt; p.TimeStamp) .HasColumnName("TimeStamp") .IsRowVersion(); ToTable("Countries"); } } public class CurrencyConfiguration : EntityTypeConfiguration&lt;Currency&gt; { public CurrencyConfiguration() : base() { HasKey(p =&gt; p.Id); Property(p =&gt; p.Id) .HasColumnName("Id") .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity) .IsRequired(); Property(p =&gt; p.TimeStamp) .HasColumnName("TimeStamp") .IsRowVersion(); ToTable("Currencies"); } } class Program { private const string ConnectionString = @"Server=.\sql2005;Database=DuplicateEntities;integrated security=SSPI;"; static void Main(string[] args) { // Seed the database MyContext context1 = new MyContext(ConnectionString); Currency currency = new Currency(); currency.Symbol = "GBP"; context1.Currency.Add(currency); Currency currency2 = new Currency(); currency2.Symbol = "USD"; context1.Currency.Add(currency2); Country country = new Country(); country.Name = "UK"; country.Currency = currency; context1.Country.Add(country); context1.SaveChanges(); // Now add a new customer Customer customer = new Customer(); customer.Name = "Customer1"; // Assign a country to the customer // Create a new context (to simulate making service calls over WCF) MyContext context2 = new MyContext(ConnectionString); var countries = from c in context2.Country.Include(c =&gt; c.Currency) where c.Name == "UK" select c; customer.Country = countries.First(); // Assign a currency to the customer // Again create a new context (to simulate making service calls over WCF) MyContext context3 = new MyContext(ConnectionString); customer.Currency = context3.Currency.First(e =&gt; e.Symbol == "GBP"); // Again create a new context (to simulate making service calls over WCF) MyContext context4 = new MyContext(ConnectionString); context4.Customers.Add(customer); // Uncommenting the following line prevents the exception raised below //customer.Country.Currency = null; context4.Entry(customer.Country).State = System.Data.EntityState.Unchanged; context4.Entry(customer.Currency).State = System.Data.EntityState.Unchanged; // The following line will result in this exception: // AcceptChanges cannot continue because the object's key values conflict with another // object in the ObjectStateManager. Make sure that the key values are unique before // calling AcceptChanges. context4.Entry(customer.Country.Currency).State = System.Data.EntityState.Unchanged; context4.SaveChanges(); Console.WriteLine("Done."); Console.ReadLine(); } } } </code></pre>
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    1. CO+1 for providing a full example to reproduce your problem, ready for copy-paste-compile-run! You obviously spent significant work to ask this question.
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