Sure they are! MikroORM uses simple queries to fetch relationships so that each database table is queried once instead of complex joining. I believe that the problem you are talking about is when using complex aggregations to imitate SQL joins, which is not the case here.
Take a look here for example of how populating relationships work: b4nan.github.io/mikro-orm/nested-p...
One note about performance - there are 4 test suites testing entity manager, one for each driver, and the mongo driver one runs about 2-3x faster than mysql/postgres (sqlite one is of course fastest).
Ahh I overlooked that in the docs! I shall take this one on a spin then :) awesome Project by the way!
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