How to remove items without round trip - asp.net-mvc

Question

Code
var items = await ctx.Cartitems.Where((c) => c.Cartid == GetCartId() && c.Toodeid == product).ToListAsync();
ctx.Cartitems.RemoveRange(items);
await ctx.SaveChangesAsync();
Removes product from shopping cart in EF Core.
It isseus to commands to database: SELECT and DELETE.
How to remove items from database so that only single command is sent to server ?
ASP.NET 5 MVC Core application using EF Core with Npgsql

Answer 1

If you have the CartItemIds, or the IDs that make up a composite PK, then you can short-cut the delete operations by attaching a stub cart ID and marking it for deletion. Depending on the lifetime scope of your DbContext and where this call sits, you many need to check each one against the local DbContext cache before attaching.
So, assuming your UI can pass a collection of CartItemIds to flush:
// This looks for any locally loaded cart items. We will remove these rather than
// attaching stubs which would raise an exception. This doesn't hit the DB.
var localCachedCartItems = _context.CartItems.Local
.Where(x => cartItemIds.Contains(x.CartItemId))
.ToList();
// Get the IDs to exclude from the Id list to create stubs.
var localCachedCartItemIds = localCachedCartItems
.Select(x => x.CartItemId)
.ToList();
// Build stubs for the remaining cart items.
var cartItemsToRemove = cartItemIds.Except(localCachedCartItemIds)
.Select(id => new CartItem { CartItemId = id })
.ToList();
foreach(var stub in cartItemsToRemve)
{
_context.Attach(stub);
_context.Entity(stub).State = EntityState.Deleted;
}
_context.SaveChanges();
If you are using locally scoped DbContexts (I.e. /w using blocks) then you can skip the Local check and just create the stubs:
using(var context = new AppDbContext())
{
var cartItemsToRemove = cartItemIds
.Select(id => new CartItem { CartItemId = id })
.ToList();
foreach(var stub in cartItemsToRemve)
{
_context.Attach(stub);
_context.Entity(stub).State = EntityState.Deleted;
}
context.SaveChanges();
}

Answer 2

Entity Framework primarily works as a change tracker, that records changes to tracked entities which are then executed and committed when calling SaveChanges. But in order to track changes like a removal, it needs to actually track those entities first. And for that, it needs to query those from the database to know which entities actually exist.
If you only want to delete entities by their primary identifier, then you could use some low-level stuff by attaching fake entities to the change tracker and then removing those, which causes EF to delete the objects from the database. Things like this require some more internal knowledge though and are not really easy to understand. So I’d recommend you to avoid approaches like these.
What you can do is use an extension that offers bulk updates on top of Entity Framework. These will usually go aroud the change tracker (meaning that the changes are executed immediately) and do not require you to load the entities into the context first. There are a few libraries that do this:
Entity Framework Extensions, a paid library with advanced functionality.
Entity Framework Plus, the free community version of EF Extensions. (GitHub)
EFCore.BulkExtensions