Gorm Associations BeforeCreate Callback not working as expected - go

Question

I have Customer struct
type Customer struct {
Model
Email string `json:"email,omitempty"`
Addresses []Address
}
func (c *Customer) BeforeCreate() (err error) {
if err := c.GenerateID(); err != nil {
return err
}
return c.Marshal()
}
And Address struct
type Address struct {
Model
CustomerID string
Address1 string
}
func (a *Address) BeforeCreate() error {
// The ID is still generated, but the insert query has no `id` in it
if err := a.GenerateID(); err != nil {
return err
}
return nil
}
Model struct
type Model struct {
ID string `gorm:"primary_key;type:varchar(100)"`
CreatedAt time.Time
UpdatedAt time.Time
DeletedAt *time.Time `sql:"index"`
}
func (model *Model) GenerateID() error {
uv4, err := uuid.NewV4()
if err != nil {
return err
}
model.ID = uv4.String()
return nil
}
A Customer:
customer := &model.Customer{
Email: "a",
Addresses: []model.Address{
{
Address1: "abc street",
},
},
}
if err := gormDb.Create(customer).Error; err != nil {
return nil, err
}
I got an error: Error 1364: Field 'id' doesn't have a default value for the Address object
But if I remove the Address associations, things work. And the customer's Id is generated.
customer := & model.Customer{
Email: "a",
//Addresses: []model.Address{
//{
//Address1: "abc street",
//},
//},
}
How can I keep the Address associations and insert both successfully, and still using this ID-generation mechanism?

Answer 1

You can use scope.SetColumn to set a field’s value in BeforeCreate hook
func (a *Address) BeforeCreate(scope *gorm.Scope) error {
scope.SetColumn("ID", uuid.New())
return nil
}
Ref: https://v1.gorm.io/docs/create.html#Setting-Field-Values-In-Hooks

Answer 2

You should use tx.Statement.SetColumn to set a field value in GORM hooks e.g. BeforeCreate. Following is the sample implementation.
func (s Product3) BeforeCreate(tx *gorm.DB) (err error) {
tx.Statement.SetColumn("Price", s.Price+100)
return nil
}
Reference implementation link for GORM Github repo
https://github.com/go-gorm/gorm/blob/ac722c16f90e0e0dffc600c7f69e791c110d788c/tests/hooks_test.go#L306-L309
Reference link from GORM docs
https://gorm.io/docs/update.html#Change-Updating-Values