Edit: Original answer used Find
instead of Local.SingleOrDefault
. It worked in combination with @Juan’s Save
method but it could cause unnecessary queries to database and else
part was probably never executed (executing the else part would cause exception because Find already queried the database and hadn’t found the entity so it could not be updated). Thanks to @BenSwayne for finding the issue.
You must check if an entity with the same key is already tracked by the context and modify that entity instead of attaching the current one:
public override void Update(T entity) where T : IEntity {
if (entity == null) {
throw new ArgumentException("Cannot add a null entity.");
}
var entry = _context.Entry<T>(entity);
if (entry.State == EntityState.Detached) {
var set = _context.Set<T>();
T attachedEntity = set.Local.SingleOrDefault(e => e.Id == entity.Id); // You need to have access to key
if (attachedEntity != null) {
var attachedEntry = _context.Entry(attachedEntity);
attachedEntry.CurrentValues.SetValues(entity);
} else {
entry.State = EntityState.Modified; // This should attach entity
}
}
}
As you can see the main issue is that SingleOrDefault
method needs to know the key to find the entity. You can create simple interface exposing the key (IEntity
in my example) and implement it in all your entities you want to process this way.