How to mak noSQL representations of big SQL tables with many relationships (postgres)

Hey guys, I need a little help.

I want to generate noSQL representation (document representation) of some postgres tables with many realtionships between them. Each table have more han 100k rows.

In a example where I have an user table and one culture table (Many to many), when I make a select of one user with join culture, for each user I get 500 rows in culture.

You know some ETL or thecnique that help me with kind of problem?