Mapping a DTO to an Entity with Automapper

automapper, c#, entity-framework

Solution

.Attach() my mapped Entity and set the state to modified?

public ActionResult EditEntity(EntityDto model)
{
    var entity = Mapper.Map<Entity>(model);
    context.Set<Entity>().Attach(entity); // (or context.Entity.Attach(entity);)
    context.Entry<Entity>(entity).State = System.Data.EntityState.Modified;
    context.SaveChanges();
    return View(model);
}

Where is your context instantiated? You should do that in your EditEntity action imo.

public ActionResult EditEntity(EntityDto model)
{
    using(var context = new MyContext())
    {
        var entity = Mapper.Map<Entity>(model);
        context.Set<Entity>().Attach(entity); // (or context.Entity.Attach(entity);)
        context.Entry<Entity>(entity).State = System.Data.EntityState.Modified;
        context.SaveChanges();
        return View(model);
    }
}

Problem

I have an Entity Framework POCO with the following structure. ``` public class Entity { public virtual int Id { get; set; } public virtual string Name { get; set; } } ``` I've created a Data Transfer Object for this entity to be used by my views. ``` public class EntityDto { public int Id { get; set; } public string Name { get; set; } } ``` Now, I have the following mapping code in my Global.asax file. ``` Mapper.CreateMap<Entity, EntityDto>(); Mapper.CreateMap<EntityDto, Entity>(); // not sure whether I need this as well? ``` Everything is working fine, I pass the DTO to my views OK and I can create a new instance of `Entity` from my `EntityDto` model. The problem arises when I try to edit my `Entity`; I'm aware this is down to AutoMapper losing the Entity Key that EF creates to track changes to the object, but having read through a few sources there doesn't seem to be a definitive solution. Here is the action I'm using to edit my entity. ``` public ActionResult EditEntity(EntityDto model) { var entity = context.Entities.Single(e => e.Id == model.Id); entity = Mapper.Map<EntityDto, Entity>(model); // this loses the Entity Key stuff context.SaveChanges(); return View(model); } ``` Now, what do I do to solve this? Can I: - Somehow tell AutoMapper to `.Ignore()` the Entity Key properties? - Get AutoMapper to copy out the Entity Key properties? - `.Attach()` my mapped `Entity` and set the state to modified? Any help always appreciated.

Original source