Summary

When using IMongoCollection<T>` to do a find and project a property from a document, the resulting data will be null,

Versions

As far as I can tell, this starts in 2.19.x, this affects the Linq V3 adapter only.

How to Reproduce

Start by defining a schema, example:

^{class Point {} 

     ^{public int X { get; set; }}

      ^      ^{^public int Y { get; set; }}

^}

Then create an IMongoCollection<Point>(omitting this for brevity), the following code is where things start getting weird.

If I do a simple .Find(...).ToList(), the results will be properly serialized into points exactly as I entered them, however, try to project just X or just Y, and you'll get the default values (0 in this case).

Example code

^{collection.Find(point => point.X == 90).Project(point => point.X).ToList()}

Regardless of  your data, this will return a list of 0s. The underlying query is correctly formatted into something like "find({ "X" : 90 }, { "_v" : "$X", "_id" : 0 })", however, the results are missing the actual X points.