What is the best way to remove entities from an untracked child collection

[e-davidson]

What is the best way to remove a child entities from an untracked entity that came from a web application?
If I want to avoid fetching the missing children just for the sake of removing them, I'd need to write the sql manually.

string sql = $@"Delete from {tableName}   where Id not in ({String.Join(",",parent.children.select(child=> child.Id)) })   and {foreignKeyColumn} = {parent.Id} ";
await _context.Database.ExecuteSqlCommandAsync(sql); 

The issue with that method is
A. Now I need an extra call to the database.
B. Its no longer a transaction when I call SaveChanges(). I now must use _context.Database.BeginTransaction().
C. I'm not getting any help generating the sql.

Proposals.

Have an Context.Entry(parent).UpdateCollection(e=> e.child) method.
That will update and remove the missing child items on SaveChanges().

Or

Add a DbSet RemoveRange Overloaded method DbSet.RemoveRange(Expression<Func<T,bool>> predicate ) that can be compiled to sql and run on the server side. So you can do

myDbSet.RemoveRange(e=> e.ParentId == Id && !e.Parent.Children.Select(c=> c.Id).Contains(e.Id) )

This way I don't have to write sql and I'm avoiding an unnecessary call to the database.

[ajcvickers]

@e-davidson This issue and the ideas you propose are being tracked by #5536 (better support for disconnected entities) and #795 (set-based updates). Closing this as a duplicate of those issues.

[jzabroski]

@ajcvickers oy vey.... I think you should close #5536 and create a new ticket with clear scenarios. How is anyone supposed to contribute to such unwieldy tickets?

Here is one possible ticket:

• Update Cascade Delete documentation's delete scenario table to explain interaction with lazy loading and proxies - ticketed here: Update Cascade Delete documentation's delete scenario table to explain interaction with lazy loading and proxies EntityFramework.Docs#844

Note, this wouldn't solve any problems, just call out unaddressed gaps in the API which can catch people by surprise, as well as educate Microsoft on clear product gaps, by looking at features as Orthogonal Arrays of pairwise feature interactions.

[jzabroski]

I created a pull request to start refactoring the documentation, so it will be clearer which scenarios result in run time exceptions, here: dotnet/EntityFramework.Docs#810