Does RavenDb's `Include` support constructing a document id, not just selecting one? - ravendb

Question

This code here is not working as expected. Specifically, it seems the calls to Include are not causing any extra documents to be added to the session. Thus, the Loads are each costing a full db hit. This is RavenDb 3.5.
I couldn't find examples that actually use Include this way. They all seem to emit a "selector" that is used to find a member on the document, and that member holds the literal document id to include. Whereas I am constructing the document id and returning it as a string.
session.Query<Coil>()
.Include(c => nameof(CoilState) + "/" + id)
.Include(c => nameof(CoilExt) + "/" + id)
.Include(c => nameof(Material) + "/" + c.MaterialCode)
.Where(c => c.CoilId == id)
.ToList()
.Select(c =>
Coil_Dto.ToCoilDto(
c
, session.Load<CoilState>(nameof(CoilState) + "/" + c.CoilId)
, session.Load<CoilExt>(nameof(CoilExt) + "/" + c.CoilId)
, session.Load<Material>(nameof(Material) + "/" + c.MaterialCode)
)
)
.SingleOrDefault()
My question is: can Include be used in this way? If not, is there some way to achieve that "include" functionality using my constructed ids?

Answer 1

It sounds like you want to use Lazy, rather than Include.
Include
The .Include method should be passed the name of a property on your object(s) which contains an ID.
// Good:
// Note that StateId, ExtId, and MaterialId are all properties on our Coil class.
session.Query<Coil>()
.Include(c => c.StateId)
.Include(c => c.ExtId)
.Inclide(c => c.MaterialId);
// Bad:
session.Query<Coil>
.Include(c => "CoilStates/123")
.Include(c => "CoilExts/456")
.Include(c => "Materials/789")
In short, make sure your .Include calls are passed the name of properties on the Coil class. Those properties should contain string values which are IDs of other documents. Then they'll all be loaded in a single trip to the database.
Lazy
If Include doesn't make sense for your scenario, but you still want to load disparate objects in a single DB call, use the lazy API
// Lazily load the coil. No DB trip yet.
var lazyCoil = session.Query<Coil>()
.Where(...)
.Lazily();
// Lazily load a CoilState. No DB trip yet.
var lazyCoilState = session.Advanced.Lazily.Load<CoilState>("CoilStates/123");
// Lazily load a Material. Still no DB trip.
var lazyMaterial = session.Advanced.Lazily.Load<Material>("Materials/456");
// Grab one of the values. This will fetch all lazy loaded items in 1 trip.
var coil = lazyCoil.Value;
// Grab the other values. No DB trip needed; they're already loaded!
var coilState = lazyCoilState.Value;
var material = lazyMaterial.Value;