Custom sum column on a relation

[thecampagnards]

Hello,

I have an issue doing a custom sum column on a relation, here an example:

type A struct {
    bun.BaseModel `bun:"table:a,alias:a"`
    ID            uint `bun:"id,pk,autoincrement"`
    Bs            []B  `bun:"rel:has-many,join:id=a_id"`
}

type B struct {
    bun.BaseModel `bun:"table:b,alias:b"`
    ID            uint `bun:"id,pk,autoincrement"`
    Value         int  `bun:",notnull"`
    AID           uint `bun:"a_id"`
}

type AWithValues struct {
    A      `bun:",extend"`
    Values int // I want to sum Bs.Value there
}

func main() {
    db := bun.NewDB(sql.OpenDB(pgdriver.NewConnector(pgdriver.WithDSN(os.Getenv("POSTGRESQL_ADDON_URI")))), pgdialect.New())

    _, _ = db.NewCreateTable().
        Model((*A)(nil)).
        Exec(context.Background())

    _, _ = db.NewCreateTable().
        Model((*B)(nil)).
        ForeignKey(`("a_id") REFERENCES "a" ("id") ON DELETE CASCADE`).Exec(context.Background())

    db.NewInsert().Model(&A{}).Exec(context.Background())
    db.NewInsert().Model(&B{
        AID:   1,
        Value: 1,
    }).Exec(context.Background())
    db.NewInsert().Model(&B{
        AID:   1,
        Value: 2,
    }).Exec(context.Background())

    db.AddQueryHook(bundebug.NewQueryHook(bundebug.WithVerbose(true)))

    var a AWithValues
    if err := db.
        NewSelect().
        Model(&a).
        TableExpr("b AS b").
        Group("a.id").
        ColumnExpr(`SUM(b.value) AS a__values, a.*`).
        Relation("Bs").
        Scan(context.Background()); err != nil {
        fmt.Println(err)
    }
    fmt.Println(a)
}

I got this:

{{{} 19 []} 3}

It works but I don't have anymore Bs and if I remove TableExpr it doesnt work anymore. I don't see what I'm doing wrong, do you have any idea ? Thx