无法跟踪实体类型“ SalesOrder”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

I am using .net core.

My Goal: I want to be able Edit a SalesOrder just after Creating .

Right now I am able to Create and Edit. But it is throwing an error

The instance of entity type 'SalesOrder' 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 (ie 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.

When I try editing just after creating.

My Save() function:

public class SalesOrdersController : Controller
{
    private readonly ApplicationDbContext _dbContext;
    public SalesOrdersController(ApplicationDbContext dbContext){
        _dbContext = dbContext;
    }
    // ...other Controller actions
    public JsonResult Save([FromBody]SalesOrderViewModel salesOrderViewModel)
    {
        SalesOrder salesOrder = new SalesOrder();
        salesOrder.document_id = salesOrderViewModel.document_id;
        salesOrder.customer = salesOrderViewModel.customer;
        salesOrder.document_status_id = salesOrderViewModel.document_status_id;
        ...
        salesOrder.object_state = salesOrderViewModel.object_state;

        _dbContext.Entry(salesOrder).State = Helpers.ConvertState(salesOrder.object_state);
        _dbContext.SaveChanges();

        salesOrderViewModel.document_id = salesOrder.document_id;
        salesOrderViewModel.object_state = ObjectState.Unchanged;
        return Json(new { salesOrderViewModel });
    }
}

And a function to update states depending on the request:

public static EntityState ConvertState(ObjectState objectState){
    switch (objectState){
        case ObjectState.Added:
            return EntityState.Added;
        case ObjectState.Modified:
            return EntityState.Modified;
        case ObjectState.Deleted:
            return EntityState.Deleted;
        default:
            return EntityState.Unchanged;
    }
}

I understand that it is a problem with refreshing the entity state just after creating. How can I resolve that error?

Answer 1

You said you understand the problem... so the solution is to get the original entity from the database and update its properties directly and then update it itself. I mean what you need to do is to avoid calling

    context.Update(entity);

Where entity is the object in your model.

So One solution would be something like the following which I agree it may not the best way of solving it.

Let's assume you are using generic repository (which is harder than non generic because you do not know the fields beforehand)

public void Edit(TBusinessObject entity)
        {

        var originalEntity = context.Set<TBusinessObject>().AsNoTracking().FirstOrDefault(r => r.Id.Equals(entity.Id));
        EntityEntry<TBusinessObject> original = context.Entry(originalEntity);
        EntityEntry<TBusinessObject> client = context.Entry(entity);
        foreach (var property in original.OriginalValues.Properties)
        {
            var dbMember = original.Member(property.Name);
            var clientMember = client.Member(property.Name);
            if(!property.IsPrimaryKey() && dbMember.CurrentValue != clientMember.CurrentValue && clientMember.CurrentValue!= null)
            {
                dbMember.CurrentValue = clientMember.CurrentValue;
                dbMember.IsModified = true;
            }
        }
        context.Update(originalEntity);
        context.SaveChanges(true);
    }

Again, This code could be optimized and it would be way simpler if it was not a generic repository, where you know the names and the types of the fields.

Update 1: I found out that EF.Core although not yet fully fledged with all the features that were supported by EF6. Yet it is somehow leaned towards the modern development practices.. The example that you posted was all about using EF.Core to implement the traditional repository mentality. If you switch to use UnitOfWork or CQRS you will not face these problems, changes like updates and CRUS in general will be smooth like never before. I am passing an object to the context, and the context itself is able to figure out to what table it belongs and how to handle it. Therefore I recommend changing the way you choose to utilize EF.Core

Try this simplest implementation:

public void Commit()
{
    using (var context = new ApplicationDbContext())
    {
            context.UpdateRange(Changed);
            context.AddRange(Added);
            context.RemoveRange(Deleted);

            context.SaveChanges();
            ClearAllChanges();
    }
}

Where "Changed, Added, Deleted" are just lists where you might consider AsynchronousBags