asp.net mvc - Entity framework inserts new record to navigation table inappropriately -

i'm facing issue when inserting records many many navigation property,

i have these models

//modelbase public class modelbase {     [key]     public long id { get; set; } }  //book public class book : modelbase {     public string title { get; set; }     public virtual icollection<author> authors { get; set; }     public virtual icollection<publishedbook> publishedbooks { get; set; } }  //author public class author : modelbase {     public string name { get; set; }     public virtual icollection<book> books { get; set; } } 

and dtos called bookdto , authordto transfer data between layers

from controller fill data dtos , call create method (which in separate layer) save data database,

bookdto bookdto = new bookdto() {     id = model.id,     title = model.title,     authors = model.authorids.select(c => new authordto { id = c }).tolist() }  using (servicefactory facory = new servicefactory()) {     factory.book.create(bookdto); } 

in create method map dtos pocos using valueinjector

public void create(bookdto bookdto) {     book book = new book();     book.injectfrom<deepcloneinjection>(bookdto);     bookrepository.add(book);     unitofwork.commit(); } 

and calls add method in genaric repository base

public virtual void add(t entity) {     dbset.add(entity); } 

this inserts data books table , bookauthors tables appropriately inserts new record authors table if pass authors has existing authorids book.authors controller.

any idea how fix this?

you missing attach existing authors context. so:

public void create(bookdto bookdto) {     book book = new book();     book.injectfrom<deepcloneinjection>(bookdto);     foreach (var author in book.authors)         authorrepository.attach(author);     bookrepository.add(book);     unitofwork.commit(); } 

where generic attach methods implemented calling dbset.attach(entity);. assuming repositories (authorrepository , bookrepository) share same context instance. otherwise above won't work.

the fact authorid exists in database doesn't matter. ef doesn't check if id exists query first. if call add on object graph of detached entities tries insert whole graph generating insert statements parent , children. attaching children turn off insert statements those.