Gorm belongs to does not return relations

I have these models

    type Message struct {
gorm.Model
UserID  uint `json:"userId"`
User    userModels.User
Content string `json:"content"`
}
type Receiver struct {
gorm.Model
UserID    uint `json:"userId"`
User      userModels.User
FirstName string `json:"firstName"`
LastName  string `json:"lastName"`
Email     string `json:"email"`
Address   string `json:"address"`
Phone     string `json:"phone"`
}
type Delivery struct {
gorm.Model
Message      Message   `json:"message"`
MessageID    uint      `json:"messageId"`
Receiver     Receiver  `json:"Receiver"`
ReceiverID   uint      `json:"receiverId"`
DeliveryDate time.Time `json:"deliveryDate"`
Sent         bool      `json:"sent"`
}

I insert some Delivery in the database with certain MessageID and ReceiverID. When I query that certain Delivery I expect to get the regarding message with the id of MessageID, and a Receiver of id ReceiverID.
But what I get is a Delivery with both empty Message and Receiver objects.

this is what I get:

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 {
"ID": 2,
"CreatedAt": "2021-08-26T04:44:33.366628+04:30",
"UpdatedAt": "2021-08-26T04:44:33.366628+04:30",
"DeletedAt": null,
"message": {
"ID": 0,
"CreatedAt": "0001-01-01T00:00:00Z",
"UpdatedAt": "0001-01-01T00:00:00Z",
"DeletedAt": null,
"userId": 0,
"User": {
"ID": 0,
"CreatedAt": "0001-01-01T00:00:00Z",
"UpdatedAt": "0001-01-01T00:00:00Z",
"DeletedAt": null,
"firstName": "",
"lastName": "",
"email": "",
"password": "",
"country": "",
"dateOfBirth": "0001-01-01T00:00:00Z",
"rank": "",
"gender": "",
"plan": ""
},
"content": ""
},
"messageId": 2,
"Receiver": {
"ID": 0,
"CreatedAt": "0001-01-01T00:00:00Z",
"UpdatedAt": "0001-01-01T00:00:00Z",
"DeletedAt": null,
"userId": 0,
"User": {
"ID": 0,
"CreatedAt": "0001-01-01T00:00:00Z",
"UpdatedAt": "0001-01-01T00:00:00Z",
"DeletedAt": null,
"firstName": "",
"lastName": "",
"email": "",
"password": "",
"country": "",
"dateOfBirth": "0001-01-01T00:00:00Z",
"rank": "",
"gender": "",
"plan": ""
},
"firstName": "",
"lastName": "",
"email": "",
"address": "",
"phone": ""
},
"receiverId": 1,
"deliveryDate": "2021-08-25T05:18:27.950457+04:30",
"sent": false
}

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While I expect it to return the message with the messageId I specified and also the receiver

When I query that certain Delivery

how do you do?

if you uses Preload
db.Preload("Message").Preload("Receiver").First(&d3)

you will get the deltial of Receiver and message like

if you don't uses Preload
what you get is a Delivery with both empty Message and Receiver objects.

if you only need messageId and receiverID
you should change the Message Message to Message *Message and Receiver Receiver to Receiver *Receiver

if you uses Preload -> same to above

if you don't uses Preload -> Receiver and Message will be nil

follow is all test code and debug info:

type User3 struct {
gorm.Model
Name      string
}
type Message struct {
gorm.Model
UserID  uint `json:"userId"`
User    *User3
Content string `json:"content"`
}
type Receiver struct {
gorm.Model
UserID    uint `json:"userId"`
User      *User3
FirstName string `json:"firstName"`
LastName  string `json:"lastName"`
Email     string `json:"email"`
Address   string `json:"address"`
Phone     string `json:"phone"`
}
type Delivery struct {
gorm.Model
Message      *Message   `json:"message"`
MessageID    uint      `json:"messageId"`
Receiver     *Receiver  `json:"Receiver"`
ReceiverID   uint      `json:"receiverId"`
DeliveryDate time.Time `json:"deliveryDate"`
Sent         bool      `json:"sent"`
}
func main() {
db := config.CreateMysql()
db.AutoMigrate(Delivery{})
d := Delivery{Message: &Message{User: &User3{Name: "a"}, Content: "hello b~"}, Receiver: &Receiver{User: &User3{Name: "b"}}, DeliveryDate: time.Now(), Sent: false}
db.Create(&d)
d2 := Delivery{}
db.First(&d2)
fmt.Printf("%v\n", d2)
d3 := Delivery{}
db.Preload("Message").Preload("Receiver").First(&d3)
fmt.Printf("%v\n", d3)
}

ps: above user is nil, if you want preload nested associations, uses follow:
.Preload("Message.User")
https://gorm.io/docs/preload.html