Auto generate UUID before create with GORM + Postgres + Go Gin + Graphql - postgresql

Question

Is there any way to auto generate UUID with GORM while saving the object in DB in go?
I am having experience with ROR migrations, where ID would be auto generated and PK by default.
Here is my code
Todo.go
package model
type Todo struct {
ID string `json:"id"`
Text string `json:"text"`
Done bool `json:"done"`
}
schema.resolvers.go
func (r *mutationResolver) CreateTodo(ctx context.Context, input model.NewTodo) (*model.Todo, error) {
db, _ := database.connect()
defer db.Close()
todo := &model.Todo{
Text: input.Text,
ID: fmt.Sprintf("%d", rand.Int()), // I don't want to provide ID like this
}
db.Create(&todo)
...
}
models_gen.go
# GraphQL schema example
#
# https://gqlgen.com/getting-started/
type Todo {
id: ID!
text: String!
done: Boolean!
}
input NewTodo {
text: String!
userId: String!
}
type Mutation {
createTodo(input: NewTodo!): Todo!
}
Any help would be really appreciated.

Answer 1

Assuming you're using gorm v2, you can use hooks to achieve this. The documentation about hooks is here
In particular, you can have a look at the BeforeCreate hook. Applied on a model, it provides a container for a function to be run before the creation in the database as its name state.
The GORM documentation also provides an example to generate a UUID when we create a user entity in a database with Gorm, which seems to be what you're looking for:
func (u *User) BeforeCreate(tx *gorm.DB) (err error) {
u.UUID = uuid.New()
if !u.IsValid() {
err = errors.New("can't save invalid data")
}
return
}

Answer 2

GORM Hooks is the most obvious solution to generate UUID when creating an object.
func (t *Todo) BeforeCreate(tx *gorm.DB) (err error) {
t.ID = uuid.New().String()
return
}
But if you want to generate UUID for every object, you could define a base struct and embed it into object structs.
type Base struct {
ID string `json:"id"`
}
func (b *Base) BeforeCreate(tx *gorm.DB) (err error) {
b.ID = uuid.New().String()
return
}
type Todo struct {
Base
Text string `json:"text"`
Done bool `json:"done"`
}
type User struct {
Base
Name string `json:"name"`
}
Or just use the GORM plugin next to generate UUID for objects.
import "github.com/invzhi/next"
plugin := NewPlugin()
// register uuid generate function
plugin.Register("uuid", func(_, zero bool) (interface{}, error) {
if !zero {
return nil, SkipField
}
return uuid.New().String()
})
_ = db.Use(plugin)
type Todo struct {
ID string `gorm:"type:varchar(20);column:id;next:uuid"` // next:uuid meaning generate uuid when create
Text string `gorm:"type:varchar(100);column:text`
Done bool `gorm:"type:boolean;column:done`
}
type User struct {
ID string `gorm:"type:varchar(20);column:id;next:uuid"` // next:uuid meaning generate uuid when create
Name string `gorm:"type:varchar(100);column:name"`
}