EF Core 已跟踪具有相同 ID 的实体

Question

I can't figure out how to get rid of the error:

The instance of entity type 'Relation' cannot be tracked because another instance with the key value '{Id: 26}' is already being tracked. When attaching existing entities, ensure that only one entity instance with a given key value is attached.

I tried detaching the entities from the context, but even that did not prevent this error from happening. Can someone point out to me what I am doing wrong?

Service:

    private async Task<int> EditAsync(RelationModel model)
    {
        RelationEntity entity = _mapper.ToEntity(model);
        RelationEntity oldRelation = await _relationRepository.GetRelationAsync(entity.Id);
        _relationRepository.UpdateRelation(oldRelation, entity);
        await _relationRepository.SaveAsync();
        return entity.Id;
    }

Repository:

    public void UpdateRelation(Relation oldRelation, Relation relation)
    {
        if (oldRelation != null)
        {
            // Detach
            Context.Entry(oldRelation).State = EntityState.Detached;

            // Delete childs
            if (oldRelation.Person != null && relation.Person == null)
            {
                Context.Persons.Remove(oldRelation.Person);
            }

            if (oldRelation.Customer != null && relation.Customer == null)
            {
                Context.Customers.Remove(oldRelation.Customer);
            }

            if (oldRelation.Supplier != null && relation.Supplier == null)
            {
                Context.Suppliers.Remove(oldRelation.Supplier);
            }

            if (oldRelation.Employee != null && relation.Employee == null)
            {
                Context.Employees.Remove(oldRelation.Employee);
            }

            // Update parent
            Context.Relations.Update(relation); // <-- error occurs
        }
    }

Relation entity:

public class Relation : BaseEntity<int>
{
    public string Code { get; set; }

    public int? PersonId { get; set; }
    public Person Person { get; set; }

    public int? CompanyId { get; set; }
    public Company Company { get; set; }

    public int? CustomerId { get; set; }
    public Customer Customer { get; set; }

    public int? SupplierId { get; set; }
    public Supplier Supplier { get; set; }

    public int? EmployeeId { get; set; }
    public Employee Employee { get; set; }

    public ICollection<RelationRelations> ParentRelations { get; set; }
    public ICollection<RelationRelations> ContactPersons { get; set; }
    public ICollection<RelationContactMethod> ContactMethods { get; set; }
    public ICollection<RelationAddress> Addresses { get; set; }
}

UPDATE

I tried replacing

Context.Relations.Update(relation); 

with

Context.Entry(oldRelation).CurrentValues.SetValues(relation);

but then none of my properties on the Relation entity get updated.

UPDATE 2

When running the following code

Context.Entry(oldRelation).CurrentValues.SetValues(relation);
Context.SaveChanges();

I can see that old relation is updated with the new values, but they aren't being applied to the DB... Why is that?

Answer 1

I am using this code instead of "Update" for many many years, everything always was updated properly and I never had any errors.

It is never good idea trying to use generic code for EF. Try to select this way if you want to update several classes:

 var oldrelation = Context.Relations
.Include(i=> i.Person)
.Include(i=> i.Company)
...
.FirstOrDefault(i=> i.Id=entity.Id);

Replace

 Context.Relations.Update(relation); 

with

Context.Entry(oldRelation).CurrentValues.SetValues(relation);