Required ID field in Data API Schema

Is it common practice to leave _id field NOT required in Data API model schema?

I expected that _id field will get generated on insert process in db, but that is not a case of Data API if Required is CHECKED! Do I even need a schemas on Data API at all?

ps. In Device Sync schemas all my _id fields are marked Required and inserts get validated without a problems (_id generated upon insert process).