Gorm with golang: Preload does not work as expected - go

Question

I have following structs
type Employee struct {
EmployeeID int64 `gorm:"primary_key;column:employee_id"`
EmployeeCode string `gorm:"column:employee_code"`
FirstName string `gorm:"column:first_name"`
LastName string `gorm:"column:last_name"`
DesignationID int64 `gorm:"column:designation_id;"`
Designation *Designation
}
type Designation struct {
DesignationID int64 `gorm:"primary_key;column:designation_id"`
DesignationName string `gorm:"column:designation_name"`
}
func GetEmployee(id int64) (*Employee, error) {
db := connection.GetConn() //get connection
defer db.Close()
employee := &Employee{}
err := db.Model(employee).Preload("Designation").Find(employee).Error
return employee, err
}
In the tables I have following records:
employee :
employee_id | employee_code | first_name | last_name | designation_id
1 | EMP1 | Raj | Mane | 1
designation:
designation_id | designation_name
1 | Engineer
The employee.designation_id is marked as foreign key referring to designation table
When I call the function GetEmployee, it returns error saying can't preload field Designation for model.Employee
I have referred many questions related to Preload but none of the solution has worked. I think only difference between the other working cases is the primary id column name. Can anyone suggest what is happening and what am I missing here?

Answer 1

In GORM default foreign key uses owner’s type name plus its primary key.
GORM provides a way to customize the foreign key, for example:
type Employee struct {
EmployeeID int64 `gorm:"primary_key;column:employee_id"`
EmployeeCode string `gorm:"column:employee_code"`
FirstName string `gorm:"column:first_name"`
LastName string `gorm:"column:last_name"`
DesignationID int64 `gorm:"column:designation_id;"`
Designation *Designation `gorm:"foreignkey:DesignationID"`
}

Answer 2

Just simply change your variable name from DesignationID to DesignationDesignationID. It will work. As per document ForignKey must be TABLE_NAME + PRIMARY_KEY_NAME so here table is DESIGNATION and primary key DESIGNATIONID
type Employee struct {
EmployeeID int64 `gorm:"primary_key;column:employee_id"`
EmployeeCode string `gorm:"column:employee_code"`
FirstName string `gorm:"column:first_name"`
LastName string `gorm:"column:last_name"`
DesignationDesignationID int64
Designation *Designation
}
type Designation struct {
DesignationID int64 `gorm:"primary_key;`
DesignationName string `gorm:"column:designation_name"`
}