Why should you care?

ShopNest order reports need customer name beside order total — joins fetch related data in one round trip when shaped correctly.

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 report = await (
    from o in _context.Orders
    join c in _context.Customers on o.CustomerId equals c.Id
    where o.OrderDate >= start && o.OrderDate < end
    orderby o.OrderDate descending
    select new OrderSummaryDto
    {
        OrderId = o.Id,
        CustomerEmail = c.Email,
        Total = o.Items.Sum(i => i.Quantity * i.UnitPrice)
    }).Take(100).ToListAsync();

What happened?

• join syntax pairs Orders and Customers on Id.
• Nested Sum on Items may translate to subquery or join depending on model — inspect ToQueryString.

Practice next

1. Prefer navigation joins when relationships exist.
2. Compare Include vs Select projection join cost.
3. Filter both sides early in Where before join.
4. Rewrite join syntax using o.Customer navigation in Select.
5. Left join pattern with DefaultIfEmpty for customers without orders.

Remember

Joins combine entities in LINQ or SQL. Navigation properties simplify many joins. Project to DTO to control join shape.

ShopNest finance export

Finance team exports last hundred orders with customer email via LINQ join.

Outcome: Single query CSV export instead of N+1 customer lookups.