Gorm: String primary keys and associations

[gchaincl]

My models uses random strings as Primery Key which is generated using _BeforeCreate_ callback. Everything works, but when I try to persist an Object with its Associations I'm getting this error:

[0.71ms]  INSERT INTO "hands" ("id","name") VALUES ('75','left') RETURNING "hands"."id"
pq: null value in column "id" violates not-null constraint
pq: null value in column "id" violates not-null constraint
[1.46ms]  INSERT INTO "fingers" ("hand_id","name") VALUES ('75','a') RETURNING "fingers"."id"

So it seem that GORM is not assigning the ID to Fingers when performing the INSERT

This is a sample code that reproduce the issue:

package main

import (
    "fmt"
    "math/rand"
    "time"

    "github.com/jinzhu/gorm"
    _ "github.com/lib/pq"
)

func randomString() string {
    rand.Seed(time.Now().UnixNano())
    return fmt.Sprintf("%d", rand.Intn(100))
}

type Finger struct {
    ID     string `gorm:"primary_key"`
    HandID string
    Name   string
}

func (f *Finger) BeforeCreate() error {
    r := randomString()
    f.ID = r
    return nil
}

type Hand struct {
    ID      string `gorm:"primary_key"`
    Name    string
    Fingers []Finger
}

func (h *Hand) BeforeCreate() error {
    r := randomString()
    h.ID = r
    return nil
}

func main() {
    db, _ := gorm.Open("postgres", "user=postgres sslmode=disable")
    db.Debug().AutoMigrate(&Hand{}, &Finger{})

    h := &Hand{
        Name: "left",
        Fingers: []Finger{
            Finger{Name: "a"}, Finger{Name: "b"},
        },
    }
    db.Debug().Create(h)
}

I'm I doing something wrong?

[jinzhu]

Hi @gchaincl

It needs to be written like this:

func (h *Hand) BeforeCreate(scope *gorm.Scope) error {
    scope.SetColumn("ID", randomString())
    return nil
}

In callbacks, if you want to update any columns to database, has to use SetColumn, this wasn't documented before, will add this to the v1 release.

Thank you.

[mlemnaru]

Please reopen this issue as it is not fixed , nor is it documented anywhere. I've just spent a whole day on this.

I had a function very similar to this one:

func (h *Hand) BeforeCreate() error {
    h.ID = someRandomID
    return nil
}

Having to set the value via scope.setColumn is not documented anywhere , just referenced in some places , but no clear indication on why you should do it that way.

Having the function applied to a pointer made me think that I am supposed to modify that object , as if that object was the final object that will get sent to the DB. That was confusing.

Thanks
Mircea