[CSHARP-780] Support natural descending sort in LINQ Created: 18/Jul/13  Updated: 26/Jan/23  Resolved: 26/Jan/23

Status: Closed
Project: C# Driver
Component/s: Linq
Affects Version/s: None
Fix Version/s: None

Type: New Feature Priority: Minor - P4
Reporter: Zaid Masud Assignee: Robert Stam
Resolution: Done Votes: 0
Labels: None
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified


 Description   

I believe there's no way to do a $natural descending sort using LINQ, which can be useful for capped collections. A $natural ascending sort is the default sort order, so supporting this is not strictly necessary.

Suggest a new OrderNaturalDescneding LINQ extension method to support this scenario.



 Comments   
Comment by Robert Stam [ 26/Jan/23 ]

As far as I know there is no way to force a natural sort (ascending or descending) in the middle of an aggregation pipeline, which in turn means there would be no way to translate a custom LINQ expression that attempted to specify a natural sort in the middle of a LINQ expression.

The closest thing I can think of is that you could specify an index hint that would affect the input to the pipeline. This hint is not part of the pipeline, but is an index hint to the aggregation command.

You could do this in C# like this:

var collection = CreateCollection();
var options = new AggregateOptions { Hint = new BsonDocument("$natural", -1) };
 
var queryable =
    collection.AsQueryable(options)
    .Take(1);

Which would result in the following command being sent to the server:

{ "aggregate" : "C", "pipeline" : [{ "$limit" : NumberLong(1) }], "hint" : { "$natural" : -1 }, "cursor" : { } }

Generated at Wed Feb 07 21:37:48 UTC 2024 using Jira 9.7.1#970001-sha1:2222b88b221c4928ef0de3161136cc90c8356a66.