How correctly aggregate and lookup mongo data to models

Question

Consider two collections:

• users (can be both, organizer and participant in other meetings)
• meetings

For the sake of simplicity, I show here only the basic data, in my code i have emails, passwords, etc.

User (easier part)

{ "_id": "ObjectId('user0_id')", "username": "Paul" }

and model:

type User struct {
    Id primitive.ObjectID `bson:"_id" json:"id,omitempty"`
    Username string `json:"username"`
}

Meeting:

{ 
  "_id": "ObjectId('meeting0_id')", 
  "organizer": "ObjectId('user0_id')", 
  "participants": [ "ObjectId('user1_id')", "ObjectId('user2_id')", "ObjectId('user3_id')"]
}

and model:

type Meeting struct {
    Id primitive.ObjectID `bson:"_id" json:"id,omitempty"`
    Organizer primitive.ObjectID `json:"organizer"`
    Participants []primitive.ObjectID  `json:"participants,omitempty"
}

Everything works if I extract only the basic data from mongo, but it seems ineffective... Because if I want to present this data in a readable form, I can't use only ObjectID, but with mongo "$lookup" I would like to get more data about users right away.

Another problem, in some cases I need a different dataset. Once to show a list I need only the name of the users assigned to the meeting. However, in the case of data administration or sending notifications, I need more (all?) User data.

How to correctly (what are the best practices) to store data like this in Go models?

Create one super-struct "meeting" with all possible data? Eg.with Participants []User instead of ID's ?

But what next? Get a complete set of data from the database each time, then filter it on the code side? Or filter on mongo side, but in most cases almost all fields in struct will be empty (eg. LastPasswordChangeDate in simple meeting participants list). Especially since there may be more "lookup" data, e.g. meeting place, invitations, etc., etc. How finally save this super struct to two collections?

P.S. Create different models for different "views" of meetings seems super stupid...