How to reference a composite primary key in GORM? - go-gorm

Question

Golang's GORM library supports composite primary keys. But how to reference them from related models?
For example, suppose I have a User and a Note model:
type User struct {
OrganizationID uint `gorm:"primaryKey; not null"`
Name string `gorm:"primaryKey; not null"`
}
type Note struct {
ID uint `gorm:"primaryKey; not null"`
OrganizationID uint `gorm:"not null"`
UserName string `gorm:"not null"`
User User
}
The auto migrator creates the notes table like this, which fails:
CREATE TABLE "notes" ("id" bigserial NOT NULL,"user_name" text NOT NULL,"organization_id" bigint NOT NULL,PRIMARY KEY ("id"),
CONSTRAINT "fk_notes_user" FOREIGN KEY ("user_name") REFERENCES "users"("name"))
But I want it to do this instead:
CONSTRAINT "fk_notes_user" FOREIGN KEY ("user_name", "organization_id") REFERENCES "users"("name", "organization_id")
How can I accomplish this?

Answer 1

You can use ForeignKey and References tags. They are mentioned in the docs, although in the reversed (One-to-Many) context.
type User struct {
OrganizationID uint `gorm:"primaryKey; not null"`
Name string `gorm:"primaryKey; not null"`
}
type Note struct {
ID uint `gorm:"primaryKey; not null"`
OrganizationID uint `gorm:"not null"`
UserName string `gorm:"not null"`
User User `gorm:"ForeignKey:OrganizationID,UserName;References:OrganizationID,Name"`
}
AutoMigrate will generate the following sql:
CREATE TABLE `users` (`organization_id` integer NOT NULL,`name` text NOT NULL,PRIMARY KEY (`organization_id`,`name`))
CREATE TABLE `notes` (`id` integer NOT NULL,`organization_id` integer NOT NULL,`user_name` text NOT NULL,PRIMARY KEY (`id`),CONSTRAINT `fk_notes_user` FOREIGN KEY (`organization_id`,`user_name`) REFERENCES `users`(`organization_id`,`name`))