Why should you care?

Placing an ShopNest order must insert Order and OrderItems together; SaveChangesAsync is the atomic batch boundary for that graph.

See it live — copy this example

Paste into a .NET project with EF Core packages, then run with LocalDB/SQL Server (dotnet ef / dotnet run).

var order = new Order
{
    CustomerId = 12,
    OrderDate = DateTime.UtcNow,
    Items =
    {
        new OrderItem { ProductId = 3, Quantity = 1, UnitPrice = 799 },
        new OrderItem { ProductId = 7, Quantity = 2, UnitPrice = 299 }
    }
};
_context.Orders.Add(order);
await _context.SaveChangesAsync(); // parent INSERT then children with FK

What happened?

• Add marks the whole graph Added.
• EF inserts Order first to obtain identity Id, then OrderItems referencing OrderId — one transaction by default.

Practice next

1. Save a parent with two children in one call and capture SQL log order.
2. Break a required FK intentionally and read DbUpdateException details.
3. Avoid SaveChangesAsync inside loops — batch once per business operation.
4. Wrap SaveChangesAsync in an explicit transaction and commit manually to see equivalence.
5. Set order.OrderDate in UTC and verify datetime column in SSMS after save.

Remember

SaveChangesAsync wraps commands in a transaction. Parent-child inserts respect FK order automatically. One save per use case improves throughput.

ShopNest checkout commit

Checkout adds Order plus line items then calls SaveChangesAsync once before payment capture.

Outcome: Customers never get charged for orders missing line items in the database.