Filtering on Include in EF Core

Finally, this feature has been implemented. It'll be available in the next preview.

Supported operations:

• Where
• OrderBy(Descending)/ThenBy(Descending)
• Skip
• Take

Some usage examples (from the original feature request):

Only one filter allowed per navigation, so for cases where the same navigation needs to be included multiple times (e.g. multiple ThenInclude on the same navigation) apply the filter only once, or apply exactly the same filter for that navigation.

customers
    .Include(c => c.Orders.Where(o => o.Name != "Foo")).ThenInclude(o => o.OrderDetails)
    .Include(c => c.Orders).ThenInclude(o => o.Customer)

or

customers
    .Include(c => c.Orders.Where(o => o.Name != "Foo")).ThenInclude(o => o.OrderDetails)
    .Include(c => c.Orders.Where(o => o.Name != "Foo")).ThenInclude(o => o.Customer)

Another important note:

Collections included using new filter operations are considered to be loaded.

That means that if lazy loading is enabled, addressing customers.Orders from the last example won't trigger a reload of the entire Orders collection.

On the other hand, if other Orders are loaded into the same context, more of them may get added to a customers.Orders collection because of relationship fixup. (I didn't verify that yet, but it seems inevitable because of how EF's change tracker works).