Loading related data: eager, explicit, lazy — Entity Framework (EF6 & EF Core)

8. Loading related data: eager, explicit, lazy

Intermediate★ Must knowLesson 8 of 15

csharp

// Eager loading
var orders = await db.Orders
    .Include(o => o.Customer)
    .Include(o => o.Lines.Where(l => l.Qty > 0))      // filtered include (EF 5)
        .ThenInclude(l => l.Product)
    .AsSplitQuery()                                     // avoid cartesian explosion with multiple collections
    .ToListAsync();

// Explicit loading
var customer = await db.Customers.FirstAsync(c => c.Id == id);
await db.Entry(customer).Collection(c => c.Orders).LoadAsync();
await db.Entry(order).Reference(o => o.Customer).LoadAsync();

// Lazy loading (opt-in): Microsoft.EntityFrameworkCore.Proxies + UseLazyLoadingProxies(); virtual navigations

	When loaded	Risk
Eager (`Include`)	Same query	Cartesian explosion with several collections → `AsSplitQuery`
Explicit	When you call `Load`	Extra round trips, but controlled
Lazy	On first access of navigation	N+1 queries, hidden DB calls, serialisation loops