Using a pointer for a foreign-key related field yields unexpected behavior when selecting multiple values #5414
Description
Your Question
Suppose you have database models as follows:
package storage
type Country struct {
ID string `json:"id" gorm:"type:uuid"`
Name string `json:"name"`
Code string `json:"code"`
}
type City struct {
ID string `json:"id" gorm:"type:uuid"`
Name string `json:"name"`
Code *string `json:"code"`
CountryId string `json:"country_id"`
Country *Country `json:"country" gorm:"references:ID"`
IATA *string `json:"iata"`
Latitude *string `json:"latitude"`
Longitude *string `json:"longitude"`
}
The city should have a pointer to a Country model to make it easier to understand whether Country has been joined (in sql) or not (e.g. if city.Country == nil {panic("for whatever reason")} )
The problem appears when I try to get the list of all cities:
package example
var cities []storage.City
tx.Joins("Country").Find(&cities)
Here, all the cities have been fetched from DB nicely, but the countries became the same in all the cities.
If I print out cities I get the following:
OUTPUT:
[
{
ID:51e415ab-4301-4268-9345-deed6b1d72f6
Name:Bergen
Code:0xc0004d6ec0
CountryId:0bd3890c-b6b7-4b27-8071-55c8f64562bb
Country:{
ID:f4e819b2-5c1a-43f9-bfa1-fe56b6ee173e
Name:Tschechien
Code:CZ
}
SkyScannerId:0xc0004d6ee0
IATA:0xc0004d6ef0
Latitude:0xc0004d6f00
Longitude:0xc0004d6f10
},
{
ID:2468c7f0-0275-4bff-8b7e-4e87bfa63604
Name:Banská Bystrica
Code:0xc0004d6bc0
CountryId:00ba76d3-9591-4d45-a39d-f554375d790f
Country:{
ID:f4e819b2-5c1a-43f9-bfa1-fe56b6ee173e
Name:Tschechien
Code:CZ
}
SkyScannerId:<nil>
IATA:<nil>
Latitude:0xc0004d6c00
Longitude:0xc0004d6c10
},
{
ID:75501988-3c80-4ef9-8081-73d20cbcc29b
Name:Prag
Code:0xc0004d6a60
CountryId:f4e819b2-5c1a-43f9-bfa1-fe56b6ee173e
Country:{
ID:f4e819b2-5c1a-43f9-bfa1-fe56b6ee173e
Name:Tschechien
Code:CZ
}
SkyScannerId:0xc0004d6a90
IATA:0xc0004d6aa0
Latitude:0xc0004d6ac0
Longitude:0xc0004d6ad0
}
]
Please pay attention to Country field of the outputs. In the ACTUAL OUTPUT all the cities have the same country. I think this has something to do with the pointer.
I got EXPECTED OUTPUT when I removed the pointer from Country (so *Country became Country without *). But I would like to get the same output with the pointer (*Country).
Also, please do not pay attention to the values printed out in other fields. My main focus is the Country field.
The document you expected this should be explained
Expected answer
What I expected to get is:
EXPECTED OUTPUT
[
{
ID:51e415ab-4301-4268-9345-deed6b1d72f6
Name:Bergen
Code:0xc0004d6ec0
CountryId:0bd3890c-b6b7-4b27-8071-55c8f64562bb
Country:{
ID:0bd3890c-b6b7-4b27-8071-55c8f64562bb
Name:Norwegen
Code:NO
}
SkyScannerId:0xc0004d6ee0
IATA:0xc0004d6ef0
Latitude:0xc0004d6f00
Longitude:0xc0004d6f10
},
{
ID:2468c7f0-0275-4bff-8b7e-4e87bfa63604
Name:Banská Bystrica
Code:0xc0004d6bc0
CountryId:00ba76d3-9591-4d45-a39d-f554375d790f
Country: {
ID:00ba76d3-9591-4d45-a39d-f554375d790f
Name:Slovakei
Code:SK
}
SkyScannerId:<nil>
IATA:<nil>
Latitude:0xc0004d6c00
Longitude:0xc0004d6c10
},
{
ID:75501988-3c80-4ef9-8081-73d20cbcc29b
Name:Prag
Code:0xc0004d6a60
CountryId:f4e819b2-5c1a-43f9-bfa1-fe56b6ee173e
Country:{
ID:f4e819b2-5c1a-43f9-bfa1-fe56b6ee173e
Name:Tschechien
Code:CZ
}
SkyScannerId:0xc0004d6a90
IATA:0xc0004d6aa0
Latitude:0xc0004d6ac0
Longitude:0xc0004d6ad0
}
]