I thought about doing exactly what you suggested, where a query could access deeper properties with a syntax like "model.cost", but ultimately decided against it because I didn't like the complexity that would necessitate.

As for arrays, I usually opt for joining the string and then doing an "includes" query. e.g. ["sm", "md", "lg"] -> "sm,md,lg" and then you could write a query like "size *= md". Obviously this approach has its disadvantages though.

I'm definitely open to rethinking both of these if that's a common enough want/need.