的NullReferenceException在EF具有两个导航属性5-6.1.1同一类型 [英] NullReferenceException in EF 5-6.1.1 with two navigation properties to the same type

问题描述

我想开始与我对这个问题的解决方法 - 但我花了几个小时今天找出异常的原因，所以我想我会分享

I'd like to start with that I have a workaround for this issue - but I spent a few hours today figuring out the cause of the exception, so I'd thought I'd share

由于两个实体的域：

public class User
{
    public int Id { get; set; }
    public string Name { get; set; }
}

public class Ticket
{
    public int Id { get; set; }

    public string Name { get; set; }

    public virtual User Owner { get; set; }

    public int? LockedByUserId { get; set; }
    public virtual User LockedByUser { get; set; }

    [Timestamp]
    public byte[] ETag { get; set; }
}

以下配置：

The following configuration:

public class TicketConfiguration : EntityTypeConfiguration<Ticket>
{
    public TicketConfiguration()
    {
        HasRequired(x => x.Owner);

        HasOptional(x => x.LockedByUser)
            .WithMany()
            .HasForeignKey(x => x.LockedByUserId);

        Property(x => x.ETag)
            .IsConcurrencyToken(true);
    }
}

和这个种子：

protected override void Seed(DataContext context)
    {
        var users = context.Set<User>();
        var user = new User
        {
            Name = "Foo"
        };
        users.AddOrUpdate(x => x.Name, user);
        user = users.SingleOrDefault(x => x.Name == "Foo") ?? user;

        var tickets = context.Set<Ticket>();
        tickets.AddOrUpdate(x=>x.Name, new Ticket
        {
            Name = "Bar",
            Owner = user,
        });
    }

我得到一个异常与此：

I get an exception with this:

static void Main()
    {
        var config = new Migrations.Configuration { CommandTimeout = 3600 };
        var migrator = new DbMigrator(config);
        migrator.Update();

        using (var transaction = GetTransaction()) // I've tried with and without transaction
        {
            var context = new DataContext();
            var userId = context.Set<User>().Where(x=>x.Name == "Foo").Select(x=>x.Id).Single();
            var ticket = context.Set<Ticket>().Single(x=>x.Name == "Bar");
            ticket.LockedByUserId = userId;

            context.SaveChanges(); 
            // Exception thrown here 'System.NullReferenceException' 
            //at System.Data.Entity.Core.Objects.DataClasses.RelatedEnd.GetOtherEndOfRelationship(IEntityWrapper wrappedEntity)
            //at System.Data.Entity.Core.Objects.EntityEntry.AddRelationshipDetectedByForeignKey(Dictionary`2 relationships, Dictionary`2 principalRelationships, EntityKey relatedKey, EntityEntry relatedEntry, RelatedEnd relatedEndFrom)
            //at System.Data.Entity.Core.Objects.EntityEntry.DetectChangesInForeignKeys()
            //at System.Data.Entity.Core.Objects.ObjectStateManager.DetectChangesInForeignKeys(IList`1 entries)
            //at System.Data.Entity.Core.Objects.ObjectStateManager.DetectChanges()
            //at System.Data.Entity.Core.Objects.ObjectContext.DetectChanges()
            //at System.Data.Entity.Internal.InternalContext.DetectChanges(Boolean force)
            //at System.Data.Entity.Internal.InternalContext.GetStateEntries(Func`2 predicate)
            //at System.Data.Entity.Internal.InternalContext.GetStateEntries()
            //at System.Data.Entity.Infrastructure.DbChangeTracker.Entries()
            //at System.Data.Entity.DbContext.GetValidationErrors()
            //at System.Data.Entity.Internal.InternalContext.SaveChanges()
            //at System.Data.Entity.Internal.LazyInternalContext.SaveChanges()
            //at System.Data.Entity.DbContext.SaveChanges()
            //at EntityFrameworkFkNull.Program.Main(String[] args) in h:\Projects\Spikes\EntityFrameworkFkNull\EntityFrameworkFkNull\Program.cs:line 27
            //at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
            //at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
            //at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
            //at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
            //at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
            //at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
            //at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
            //at System.Threading.ThreadHelper.ThreadStart()
            transaction.Complete();
        }
    }

获得完整的解决方案，在这里试试自己：<一HREF =https://github.com/mvidacovich/EntityFrameworkFkNull相对=nofollow> https://github.com/mvidacovich/EntityFrameworkFkNull

我相信这是因为门票有两种不同的外键的用户，但被明确配置只是其中之一。

I believe this is because Ticket has two different foreign keys to User but only one of them is explicitly configured.

这会影响EF 5 EF 6至于我。已经测试过自己

This affects EF 5 to Ef 6 as far as I've tested myself.

所以，这引出了一个问题：难道预计EF抛出异常呢？

So, that begs the question: Is it expected that EF throws an exception there?

推荐答案

解决方法是对票务的OWNERID属性。 （见修复分公司在github上解）

The workaround is to have an "OwnerId" property on Ticket. (See fix branch in the solution in github)

所以，票务变为：

public class Ticket
{
    public int Id { get; set; }

    public string Name { get; set; }

    public int? OwnerId { get; set; }
    public virtual User Owner { get; set; }

    public int? LockedByUserId { get; set; }
    public virtual User LockedByUser { get; set; }

    [Timestamp]
    public byte[] ETag { get; set; }
}

和票务的配置更改为：

public class TicketConfiguration : EntityTypeConfiguration<Ticket>
{
    public TicketConfiguration()
    {
        HasRequired(x => x.Owner)
            .WithMany()
            .HasForeignKey(x=>x.OwnerId);

        Property(x => x.OwnerId)
            .HasColumnName("Owner_Id");

        HasOptional(x => x.LockedByUser)
            .WithMany()
            .HasForeignKey(x => x.LockedByUserId);

        Property(x => x.ETag)
            .IsConcurrencyToken(true);
    }
}

现在注意明确OWNERID。
为全（固定的）解决方案，请参阅本： https://github.com/mvidacovich / EntityFrameworkFkNull /树/修复

Notice the explicit OwnerId now. See this for the full (fixed) solution: https://github.com/mvidacovich/EntityFrameworkFkNull/tree/Fix

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