I need this also to finish my project with a special movie database.
Another solution could be a separate data collection to cross reference other collections.
This is not working for now, cause you can not access the cross referenced collections “datas”. 
More on this: Many to Many Relationship? - #3 by Shotster - CMS - Forum | Webflow
webflow has the potential to be a awesome made pioneer in webdesign and creating webpages. but there are still some very important features missing => e.g. every big database needs advanced search functionalities otherwise it gets useless with to many datasets stored.
go for it Webflow Team 
i 
for more features!