Based on old memories since I’ve been working in mongo lately, after making the UDT on the db side, you make a data table that has the same name, namespace (ie dbo/public), and the same schema as the UDT (better if that could be generated) and populate it in code. Then you execute the db query with the UDT type as a parameter.

This is better for a few reasons, including not building up a string, but also having the same text means that each query didn’t need to be re-parsed and can reuse execution plans. If the query text isn’t an exact match, it gets that whole pipeline each time.