I have two IMongoCollections holding documents of type Person and Animal respectively.
public class Person
{
public Guid PersonId { get; set; } = Guid.NewGuid();
public Guid PetId { get; set; }
}
public class Animal
{
public Guid AnimalId { get; set; } = Guid.NewGuid();
public bool IsMammal { get; set; }
}
...
Animal bootsTheMonkey = new Animal() { IsMammal = true };
Person doraTheExplorer = new Person() { PetId = bootsTheMonkey.AnimalId };
I am trying to write a query which finds "all persons whose pets are mammals".
var query =
from pDoc in PersonDocumentCollection.AsQueryable()
where !pDoc.PetId.Equals(Guid.Empty)
join aDoc in AnimalDocumentCollection.AsQueryable() on pDoc.PetId equals aDoc.AnimalId
where aDoc.IsMammal
select pDoc;
Though this query is incorrect evidenced by the error message
$project or $group does not support {document}.
From searching it looks like this error comes about from the use of where aDoc.IsMammal, more specifically the use of the aDoc within/after the join (Based on this SO question). Though I am not entirely sure if that is the issue.
Overall I am trying to join two IMongoCollections where the first's documents have a field whose value is the BsonId of a document from another collection. Then once joined I would like to first the documents from the first collection on the values of fields in the second.
You could try to do something like this (assuming allPeople is a list of all your Person objects and allAnimals is all your Animal objects):
var query = allPeople
.Join(allAnimals,
p => p.PetId,
a => a.AnimalId,
(p, a) => new { P = p, A = a })
.Where(PA => PA.A.IsMammal == true);