Summary

Driver Version: 2.21.0; No issue up to 2.20.0;

MongoDB Version: 6.0.10

 

When projecting a search result to the Id field of a nested document, the top-level Id field is returned.

See the following (simplified) example.

Expected: subDocumentId contains the value of the Id field of SubDocument.

Actual: subDocumentId contains the value of the Id field of Document.

Up to driver version 2.20.0, this works as expected.

 

public class BusinessLogic
{
    public async Task<ObjectId> GetSubDocumentId()
   

{         var subDocumentId = await _dbContext.Documents.Find(d => d.Status == status)                 .Project(d => d.PairedSwitchingDevice.Id)                 .FirstOrDefaultAsync();         return subDocumentId;     }

}

public class Document

{     [BsonId]     public ObjectId Id \{ get; set; }

    [BsonElement("Status")]
    public string Status { get; set; }

    [BsonElement("SubDocument")]
    public SubDocument SubDocument { get; set; }
}

public class SubDocument

{     [BsonElement("Id")]     public ObjectId Id \{ get; set; }

}