Database
db={"Artwork":[{slug:"s1",title:"Artwork 1"},{slug:"s2",title:"Artwork 2"},{slug:"s3",title:"Artwork 3"}],"UserInteraction":[{uid:"uid1",action:"LIKED",targetType:"ARTWORK",targetKey:"SLUG",targetValue:"s1",created:100},{uid:"uid1",action:"LIKED",targetType:"ARTWORK",targetKey:"SLUG",targetValue:"s3",created:130},{uid:"uid1",action:"LIKED",targetType:"GALLERY",targetKey:"CODE",targetValue:"g3",created:140}]}
Query
db.Artwork.aggregate([{$match:{}},/** completely unsure about how to use $lookup here* to add the "created" value for the user "uid1"* for each artwork's slug here.*/])