Is a Select() done against a key in the table's struct? - go-gorm

Question

I have a database where one of the tables is managed through
type Token struct {
gorm.Model
Value string
User User
UserID uint
}
At some point, I am trying to retrieve all the elements in that table, but limited to only one field (Users). When doing the query without the Select(), I get everything as expected:
var tokens []Token
db.
Preload("User").
// Select("User").
Find(&tokens)
An extract from the output:
(...)
{
"ID": 27,
"CreatedAt": "2022-03-11T20:24:01.0505503+01:00",
"UpdatedAt": "2022-03-11T20:24:01.0505503+01:00",
"DeletedAt": null,
"Value": "admintoken",
"User": {
"ID": 27,
"CreatedAt": "2022-03-11T20:24:01.0521975+01:00",
"UpdatedAt": "2022-03-11T20:24:01.0521975+01:00",
"DeletedAt": null,
"UserName": "admin",
"UserType": {
"ID": 0,
"Name": "",
"UserID": 0
}
}
}
(...)
Since I only want to get the "User" object, I tried
var tokens []Token
db.
Preload("User").
Select("User").
Find(&tokens)
but now the output is empty.
What should the Select() be against?

Answer 1

To select all Users that have at least one token you could use the following query:
var users []User
db.Where("id IN (?)","SELECT DISTINCT(user_id) FROM tokens").Find(&users)

Answer 2

I don't think Preload is a good option since it would do 2 queries to retrieve the result, why do 2 queries if you can retrieve expected result in only 1 query
To retrieve users who has token code can be updated as below:
var users []User
db.Table("users").Select("users.id, users.name").Joins("inner join tokens on tokens.user_id = users.id").Find(&users)
rows, err := db.Table("users").Select("users.id, users.name").Joins("inner join tokens on tokens.user_id = users.id").Rows()
for rows.Next() {
...
}