"Traditional" one-to-many Query with RavenDB - node.js

Question

I know the include-feature of RavenDB. It allows me to fetch a referenced document right away in one roundtrip to the database. But my problem is: The document i fetch in the first place is not including a reference to the "other" documents. But the "other" documents have references to the current document.
Imagine a setup where we have sites across the world. Each site may trigger various alarms. Each alarm has a reference to the site via siteId.
Now i would like to get a list of all the sites including all alarms. But it looks like, this is not possible with RavenDB? Since include only accepts a "path" in the site-Document which holds an id (or an array of ids) to the referenced document.
This could be solved by providing an array of alarmIds within the site'-document and referencing this array in include. But in contrast to a lot of examples featuring stuff like an orderwithlineItemswhere the order is a self contained thing, mysite` will be running for years, collecting alarms anywhere between 0 and a million. Which seems to be a bad idea to me.
Of course i could go the other way round: Query all alarms and include the sites via sitesId. But this would not return a site that has zero alarms.
So is this just a design error on my side? To i misunderstand something? Or is it just not possible to do this in one query and prevent a "n+1 query"?

Answer 1

public class A
{
public string Id { get; set; }
}
public class B
{
public string Id { get; set; }
public string A { get; set; }
}
public class MultiMapIndex : AbstractMultiMapIndexCreationTask<MultiMapIndex.Result>
{
public class Result
{
public string Id { get; set; }
public IEnumerable<string> Bs { get; set; }
}
public MultiMapIndex()
{
AddMap<A>(items => from a in items
select new Result {Id = a.Id, Bs = new string[0]});
AddMap<B>(items => from b in items
select new Result {Id = b.A, Bs = new[] {b.Id}});
Reduce = results => from result in results
group result by result.Id
into g
select new Result {Id = g.Key, Bs = g.SelectMany(r => r.Bs)};
}
}
[Fact]
public async Task TestCase()
{
using var store = GetDocumentStore();
await new MultiMapIndex().ExecuteAsync(store);
using (var session = store.OpenAsyncSession())
{
await session.StoreAsync(new B {A = "a/1"}, "b/0");
await session.StoreAsync(new A(), "a/1");
await session.StoreAsync(new A(), "a/2");
await session.SaveChangesAsync();
}
WaitForIndexing(store);
using (var session = store.OpenAsyncSession())
{
var results = await session.Query<MultiMapIndex.Result, MultiMapIndex>()
.Include(r => r.Bs)
.ToArrayAsync();
var before = session.Advanced.NumberOfRequests;
var bs = session.LoadAsync<B>(results[0].Bs);
Assert.Equal(before, session.Advanced.NumberOfRequests);
}
}

Answer 2

If you do choose to query all Alarms, as you mention,
then you can create a Map-Reduce index on the Alarms collection which will group-by the Sites.
Then you can query this Map-Reduce index and know per Site the count of Alarms it has or doesn't have...
https://demo.ravendb.net/demos/csharp/static-indexes/map-reduce-index