EF7（Core）中同一个表的多个关系

我有这样的模特

public class Question { public string Id { get; set; } = Guid.NewGuid().ToString(); public Answer Answer { get; set; } public List Variants { get; set; } public string CorrectVariantId { get; set; } public Variant CorrectVariant { get; set; } } public class Variant { public string Id { get; set; } = Guid.NewGuid().ToString(); public string QuestionId { get; set; } public Question Question { get; set; } } // mapping modelBuilder.Entity() .HasOne(q => q.CorrectVariant) .WithOne(v => v.Question) .HasForeignKey(q => q.CorrectVariantId); modelBuilder.Entity() .HasOne(v => v.Question) .WithMany(a => a.Variants) .OnDelete(DeleteBehavior.Cascade); 

在我从EF RC1升级到RTM之前，这一function完美无缺。 但现在它抛出： System.InvalidOperationException: Cannot create a relationship between 'Question.Variants' and 'Variant.Question', because there already is a relationship between 'Question.CorrectVariant' and 'Variant.Question'. Navigation properties can only participate in a single relationship. System.InvalidOperationException: Cannot create a relationship between 'Question.Variants' and 'Variant.Question', because there already is a relationship between 'Question.CorrectVariant' and 'Variant.Question'. Navigation properties can only participate in a single relationship.

如果没有从Question模型中删除Variants属性，是否有解决此问题的方法？

Answer 1

这是RC1中的一个错误/不受欢迎的行为，它已得到修复。

你应该创建另一个属性，比如说另一个关系的SecondQuestion。

 public class Question { public string Id { get; set; } = Guid.NewGuid().ToString(); public List Variants { get; set; } public string CorrectVariantId { get; set; } public Variant CorrectVariant { get; set; } } public class Variant { public string Id { get; set; } = Guid.NewGuid().ToString(); public string QuestionId { get; set; } public Question Question { get; set; } public Question SecondQuestion { get; set; } } 

你的DbContext：

 protected override void OnModelCreating(ModelBuilder modelBuilder) { modelBuilder.Entity() .HasOne(q => q.CorrectVariant) .WithOne(v => v.SecondQuestion) .HasForeignKey(q => q.CorrectVariantId); modelBuilder.Entity() .HasOne(v => v.Question) .WithMany(a => a.Variants).HasForeignKey(x => x.QuestionId).OnDelete(DeleteBehavior.SetNull); base.OnModelCreating(modelBuilder); } 

如何使用它：

 using (var myDb = new MyDbContext()) { var variantFirst = new Variant(); var variantSecond = new Variant(); var question = new Question(); variantFirst.Question = question; variantSecond.SecondQuestion = question; myDb.Variants.Add(variantFirst); myDb.Variants.Add(variantSecond); myDb.SaveChanges(); } 

Answer 2

万一有人会遇到这个问题。 这是更优雅的解决方案

 public class Question { public Guid Id { get; private set; } public IReadOnlyList Variants { get; private set; } public Guid CorrectVariantId { get; private set; } public Guid? AnsweredVariantId { get; private set; } public bool IsAnswerCorrect => CorrectVariantId == AnsweredVariantId; public bool IsAnswered => AnsweredVariantId != null; } public class Variant { public Guid Id { get; private set; } public Guid QuestionId { get; private set; } public string HiddenUserLogin { get; private set; } public User HiddenUser { get; private set; } } // mapping mb.Entity() .HasMany(q => q.Variants) .WithOne() .HasForeignKey(nameof(Variant.QuestionId)) .IsRequired() .OnDelete(DeleteBehavior.Cascade); mb.Entity() .HasOne(typeof(Variant)) .WithOne() .HasForeignKey(nameof(Question.AnsweredVariantId)) .IsRequired(false) .OnDelete(DeleteBehavior.Restrict); // EF creates Unique Index for nullable fields mb.Entity() .HasIndex(q => q.AnsweredVariantId) .IsUnique(false); // create index instead of FK hence the cyclic dependency between Question and Variant mb.Entity() .HasIndex(q => q.CorrectVariantId) .IsUnique();