db={"sites":[{"_id":{"$oid":"5e607b4743e2640056467509"},"title":"Example.com","url":"http://example.com","pages":[{"$oid":"5de543144a90390055a71df7"}],"createdAt":{"$date":{"$numberLong":"1583381319365"}},"updatedAt":{"$date":{"$numberLong":"1657263777867"}}}],"pages":[{"_id":{"$oid":"5de543144a90390055a71df7"},"translated":true,"mediaBlocks":[{"$oid":"60a5e0e89030f50037cb6671"},],"title":"Some page on Example.com","uri":"http://example.com/somepage","createdAt":{"$date":{"$numberLong":"1652302986085"}},"updatedAt":{"$date":{"$numberLong":"1658981812449"}},}],"mediablocks":[{"_id":{"$oid":"60a5e0e89030f50037cb6671"},"status":"translated","normalizedText":"some text from example.com","rawText":"Some text from example.com","createdAt":{"$date":{"$numberLong":"1573479155826"}},"updatedAt":{"$date":{"$numberLong":"1574252856156"}}}]}

db.sites.aggregate([{$lookup:{from:"pages",localField:"pages",foreignField:"_id",as:"pages",pipeline:[{$lookup:{from:"mediablocks",localField:"mediaBlocks",foreignField:"_id",as:"mediaBlocks"}}]}}])