Database
db={"users":[{roleId:ObjectId("507f1f77bcf86cd799439011")},{roleId:ObjectId("507f1f77bcf86cd799439012")}],"courses":[{name:"Course 1",relationRoleCourses:[{userRoleId:"507f1f77bcf86cd799439012"}]},{name:"Course 2",relationRoleCourses:[{userRoleId:ObjectId("507f1f77bcf86cd799439011")}]}]}
Query
db.users.aggregate([{$lookup:{from:"courses",localField:"roleId",foreignField:"relationRoleCourses.userRoleId",as:"courses"}}])