GORM: Create() with different Input and Output Structs - go-gorm

Question

Is it possible in GORM to give Create() a Struct A as input and store the result in Struct B?
I haven't found anything suitable in the documentation or on the internet.
The background is as follows:
I let Postgres create the fields id, createdAt and updatedAt - therefore they should not be part of the input Struct A (quasi the DTO/DAO).
However, in the result of Create() these fields are then present - so they should be parsed into Struct B, which contains all the fields of the table.
Problem if id, createdAt and updatedAt are not explicitly set:
Go initialises fields of structs that are not explicitly defined with default values, depending on the data type (0, nil etc.).
For the id of type UUIDv4, the value is then 00000000-0000-0000-0000000000.
Apparently this passed value then overwrites Postgres' gen_random_uuid() value for the id column.
Once this works fine, then a duplicyte key error occurs.
createdAt and updatedAt, on the other hand, seem to be generated correctly by Postgres, although I have found Go's default values there as well.
Thank you!
PS: Of course, I could simply create a UUID and give it to the database, but I am basically interested in whether or not my intention can be realised with GORM.

Answer 1

You don't need two separate structs, you can use your model to insert/fetch. One way of doing it is to embed gorm.Model, which will embed
// gorm.Model definition
type Model struct {
ID uint `gorm:"primaryKey"`
CreatedAt time.Time
UpdatedAt time.Time
DeletedAt gorm.DeletedAt `gorm:"index"`
}
Embedding into User struct.
type User struct {
gorm.Model
Name string
Age int
}
// equals
type User struct {
ID uint `gorm:"primaryKey"`
CreatedAt time.Time
UpdatedAt time.Time
DeletedAt gorm.DeletedAt `gorm:"index"`
Name string
Age int
}
Now creating records
user := User{Name: "randomname", Age: 18}
result := db.Create(&user) // pass pointer of data to Create
user.ID // returns inserted data's primary key
user.CreatedAt // returns inserted data's created at key
user.UpdatedAt // returns inserted data's updated at key
Embedding gorm.Model is optional, you can embed it or add the fields to the struct directly or you can create your own struct to embed.
Even if at the time of insert those fields [updatedAt, createdAt] are empty or not part of the input struct, the result will return whatever that is there in database. If the createdAt or updatedAt are created by postgres and nonEmpty it will be returned.
update :- We can use default values
type HasUuidPkey struct {
ID uuid.UUID `gorm:"primaryKey;default:gen_random_uuid()"`
Name string
CreatedAt time.Time
}
Playground example