c# - Force Automapper to use ConstructUsing even if nested entity is already created -

please suppose domain

public class customer : entity {     public int id { get; set; }     public string name { get; set; }      public image photo { get; set;}     public int photoid { get; set; } }  public class image : entity {     public int id { get; set; }     public byte[] content { get; set; } } 

now suppose models

public class customermodel : entitymodel {     public int id { get; set; }     public string name { get; set; }      public imagemodel photo { get; set;}     public int photoid { get; set; } }  public class imagemodel : entitymodel {     public int id { get; set; }     public byte[] content { get; set; } } 

suppose have customer on database, attached dbcontext:

customer = {     id : 1,     name : "alexandre",     photoid: 13,     photo : {         id: 13,         content: abc     } } 

and model (posted user browser):

customermodel = {     id : 1,     name : "alexandre",     photoid: 0,     photo : {         id: 0,         content: xyz     } } 

so, how can see, user creates new photo (id == 0) not still saved database, , replace on entity.

the problem : if call

mapper.map(customermodel, customer) 

automapper map customermodel.photo customer.photo, instead of creates new one, , entity framework raise exception because can't change pk of image object.

also, can't

customer.photo = null  

before map objects because mapping generics, , base classes not knows structure of these objects. big application many entities, don't want execute code every nested property on every entity.

so need more genereic...

what want: automapper must knows these photos not same (by comparing ids) , creates new 1 instead of replace same.

is possible?

this map forces creation of new image object accordingly id comparison:

mapper.createmap<customermodel, customer>()     .beforemap((src, dest) =>          dest.photo = dest.photo.id != src.photo.id ? new image() : dest.photo); 

edit: more generic approach:

mapper.createmap<customermodel, customer>().beforemap(action); mapper.createmap<foomodel, foo>().beforemap(action);  private static void action(entitymodel src, entity dest) {     //get actual object properties via reflection, compare, re-create... }