Consider the following object structure stored as documents:
public class Foo
{
public string Id { get; set; }
public ICollection<FooBar> Bars { get; set; }
// ...
}
public class FooBar
{
public string BarId { get; set; }
// ...
}
Using a LINQ-style query with the driver I can Find all Foo that contain a FooBar BarId like this:
var foos = await m_fooCollection.Find( f => f.Bars.Any( fb => fb.BarId == "123") ).ToListAsync();
How can I achieve this same query using the FilterDefinitionBuilder instead of the in-line LINQ on Find?
The query you need to perform uses the $elemMatch query operator.
So, this query using a lambda expression
var findFluent = collection.Find(f => f.Bars.Any(fb => fb.BarId == "123"));
Is equivalent to this query using the FilterDefinitionBuilder:
var findFluent = collection.Find(Builders<Foo>.Filter.ElemMatch(
foo => foo.Bars,
foobar => foobar.BarId == "123"));