无法跟踪实体类型“ TestType”的实例，因为已经跟踪了具有相同键的该类型的另一个实例

Question

尝试执行以下操作时，出现以下异常：

    context.Entry(testType).State = EntityState.Modified;


System.InvalidOperationException: The instance of entity type 'TestType' cannot be tracked because another instance of this type with the same key is already being tracked. When adding new entities, for most key types a unique temporary key value will be created if no key is set (i.e. if the key property is assigned the default value for its type). If you are explicitly setting key values for new entities, ensure they do not collide with existing entities or temporary values generated for other new entities. When attaching existing entities, ensure that only one entity instance with a given key value is attached to the context.
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.IdentityMap`1.Add(TKey key, InternalEntityEntry entry)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.IdentityMap`1.Add(InternalEntityEntry entry)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.StartTracking(InternalEntityEntry entry)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.InternalEntityEntry.SetEntityState(EntityState oldState, EntityState newState, Boolean acceptChanges)
   at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.InternalEntityEntry.SetEntityState(EntityState entityState, Boolean acceptChanges)
   at Microsoft.EntityFrameworkCore.ChangeTracking.EntityEntry.set_State(EntityState value)

我没有看到任何代码，其中已经跟踪了另一个具有相同键的TestType实例！

来自数据库的测试类型通过.AsNoTracking();加载.AsNoTracking();

因此，在此代码中的哪里有我具有RemoveRange / AddRange操作的具有相同键的TestType实例？ 那意味着我的TestTypeComparer坏了吗？

我在这里尝试做的是让用户一次性保存已更改/添加/删除的实体：

 public async Task<IEnumerable<TestType>> SaveTestTypesAsync(List<TestType> testTypes, int schoolyearId, int schoolclassId, int subjectId)
        {
            var testTypesFromDatabase = await context.TestTypes
                                          .Include(t => t.Subject)
                                          .Include(s => s.Schoolclass)
                                          .Where(p =>
                                          p.Schoolclass.Id == schoolclassId &&
                                          p.Subject.Id == subjectId)
                                          .AsNoTracking()
                                          .ToListAsync();

            var schoolclass = new Schoolclass { Id = schoolclassId };
            var subject = new Subject { Id = subjectId };
            var schoolyear = new Schoolyear { Id = schoolyearId };
            foreach (var testType in testTypes)
            {
                testType.Schoolclass = schoolclass;
                testType.Subject = subject;
                testType.Schoolyear = schoolyear;
            }

            var testTypesToRemove = testTypesFromDatabase.Except(testTypes, new TestTypeComparer()).ToList();
            context.TestTypes.RemoveRange(testTypesToRemove);

            var testTypesToAdd = testTypes.Where(t => t.Id == 0).ToList();  // 
            context.TestTypes.AddRange(testTypesToAdd);

            var modifiedTestTypesToUpdate = testTypes.Except(testTypesToAdd.Concat(testTypesToRemove).ToList(), new TestTypeComparer()).ToList();
            foreach (var testType in modifiedTestTypesToUpdate)
            {
                context.Entry(testType).State = EntityState.Modified;
            }

            context.Attach(schoolclass);      
            context.Attach(subject);
            context.Attach(schoolyear);

            await context.SaveChangesAsync();

            return await this.GetTestTypesConfigurationAsync(schoolclassId, subjectId);
        }


public class TestTypeComparer : IEqualityComparer<TestType>
{
    public bool Equals(TestType x, TestType y)
    {
        return x.Id == y.Id;
    }

    public int GetHashCode(TestType obj)
    {
        return obj.Id.GetHashCode();
    }
}

public class TestType
    {
        public TestType()
        {
            Tests = new HashSet<Test>();
        }

        public int Id { get; set; }
        public string Name { get; set; }
        public int Weight { get; set; }
        public ISet<Test> Tests { get; set; }
        public Schoolyear Schoolyear { get; set; }  
        public Schoolclass Schoolclass { get; set; }
        public int SchoolclassId { get; set; }
        public Subject Subject { get; set; }
        public int SubjectId { get; set; }
        public int SchoolyearId { get; set; }
    }

任何人都可以帮助我，但我无法找到具有相同密钥的双重跟踪实体。

我只是假设问题与确定我添加/修改/删除的实体有关。

UPDATE

我现在已经在设置State.Modified为所有TestTypesToUpdate之前记录了所有跟踪器更改：

State: Deleted | Type: TestType | Id-Value: 12
State: Unchanged | Type: Schoolclass | Id-Value: 1
State: Unchanged | Type: TestType | Id-Value: 8
State: Unchanged | Type: Subject | Id-Value: 1
State: Deleted | Type: TestType | Id-Value: 13
State: Added | Type: TestType | Id-Value: -2147482647
State: Detached | Type: Schoolclass | Id-Value: 1
State: Added | Type: Schoolyear | Id-Value: 1
State: Detached | Type: Subject | Id-Value: 1
State: Added | Type: TestType | Id-Value: -2147482646

看来是的...已经跟踪了某些实体。 似乎我必须在变更跟踪器上进行其他投资，然后再决定要怎么做。

但我不敢相信我是第一个这样做的人，还没有在Google上找到任何东西。

Answer 1

考虑了多个具有相同键问题的实例后，我再次重新排列了代码，直到再次出现错误为止，我无法将testTypeToUpdate的状态设置为state.Modified，因为SchoolclassId是键的一部分。

好吧...然后我搜索了流畅的迁移结果，发现了这一点：

modelBuilder.Entity<TestType>().HasAlternateKey(x => new { x.Name, x.SchoolclassId, x.SubjectId });

我前一阵子做了（但从未测试过-真可惜-），我认为它的EF6等同于Index Attribute ...因为那是我想要的功能！

然后我用谷歌搜索并创建了一些新的东西：

modelBuilder.Entity<TestType>().HasIndex(p => new { p.Name, p.SchoolclassId, p.SubjectId} ).IsUnique();

现在我有了我想要的！

我还删除了分配给testTypesToRemove的schoolclass，subject和schoolyear实例，这也创建了一些奇怪的东西...

该代码现在可以工作：

   public async Task<IEnumerable<TestType>> SaveTestTypesAsync(List<TestType> testTypes, int schoolyearId, int schoolclassId, int subjectId)
        {
            var testTypesFromDatabase = await context.TestTypes
                                          .Include(t => t.Subject)
                                          .Include(s => s.Schoolclass)
                                          .Where(p =>
                                          p.Schoolclass.Id == schoolclassId &&
                                          p.Subject.Id == subjectId)
                                          .AsNoTracking()
                                          .ToListAsync();

            var schoolclass = new Schoolclass { Id = schoolclassId };
            var subject = new Subject { Id = subjectId };
            var schoolyear = new Schoolyear { Id = schoolyearId };

            // Make the navigation properties available during SaveChanges()
            context.Attach(schoolclass);
            context.Attach(subject);
            context.Attach(schoolyear);

            // DELETE
            var testTypesToRemove = testTypesFromDatabase.Except(testTypes, new TestTypeComparer()).ToList();
            context.TestTypes.RemoveRange(testTypesToRemove);

            // ADD
            var testTypesToAdd = testTypes.Where(t => t.Id == 0).ToList();  // 
            foreach (var testType in testTypesToAdd)
            {
                testType.Schoolclass = schoolclass;
                testType.Subject = subject;
                testType.Schoolyear = schoolyear;
            }
            context.TestTypes.AddRange(testTypesToAdd);

            // UPDATE
            var modifiedTestTypesToUpdate = testTypes.Except(testTypesToAdd.Concat(testTypesToRemove).ToList(), new TestTypeComparer()).ToList();
            foreach (var testType in modifiedTestTypesToUpdate)
            {
                testType.Schoolclass = schoolclass;
                testType.Subject = subject;
                testType.Schoolyear = schoolyear;
            }   
            context.UpdateRange(modifiedTestTypesToUpdate);

            await context.SaveChangesAsync();

            return await this.GetTestTypesConfigurationAsync(schoolclassId, subjectId);
        }