Thx for taking the time to read this. I've been looking for an answer to this problem for a week already and I'm running out of ideas... This is the scenario:
The model:
public class Parent{
public Guid Id {get;set;}
public virtual ICollection<Child> ChildCollection{ get; set; }
}
public class Child {
public Guid Id {get;set;}
public string Name{get;set}
}
On Model creating:
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Entity<Parent>()
.HasMany(c => c.ChildCollection)
.WithMany()
.Map(x =>
{
x.ToTable("ParentToChildMapping");
x.MapLeftKey("ParentId");
x.MapRightKey("ChildId");
});
}
Now the problem:
If I have a Parent object with a Child object in the collection and try to add a new object of same id to the child collection the DbContext doesn't "detect" the change and doesn't add a new entry in the mapping table. But if I add a new Child (that doesn't exist in the collection) it does get added ok.
For Example:
{
var childId = Guid.Parse("cbd5bccc-b977-4861-870d-089994958cdf");
var parent = new Parent { ChildCollection = new HashSet<Child>() };
var context = new DBContext();
var child = context.Childs.Single(c=>c.Id=childId);
parent.ChildCollection.Add(child);
context.Parents.Add(parent);
context.SaveChanges();
}
Then:
{
var childId = Guid.Parse("cbd5bccc-b977-4861-870d-089994958cdf");
var context = new DBContext();
var parent = dbContext.Parents.Include(p=>p.ChildCollection).Single(p=>p.Id=parentId); // The id saved in the point before.
var child = context.Childs.Single(c=>c.Id=childId);
parent.ChildCollection.Add(child);
// At this point parent.ChildCollection.Count() = 2
context.SaveChanges();
}
The count of the collection is 2, which is fine. But save changes doesn't add the item. If I retrieve it back from the db using context again, it only returns 1 element in the collection.
Any thoughts are wellcome.
You're trying to add the same child to a parent twice, and this won't work. If you were successful, you would end up with something like the following in the database:
which is not allowed for a relational database, because (ParentId, ChildId) is the primary key of ParentToChildMapping, and two rows in a table cannot have the same primary key.