问如何在Gorm中附加多对多关系，而不颠倒已存在的关联行？

EN

type A struct {
    ID int `gorm:"primaryKey"`
    Bs []B `gorm:"many2many:a_bs;"`
}

type B struct {
    ID int `gorm:"primaryKey"`
    As []A `gorm:"many2many:a_bs;"`
}

a1 := A{}
db.Create(&a1)

a2 := A{}
db.Create(&a2)

INSERT INTO "as" DEFAULT VALUES RETURNING "id"
INSERT INTO "as" DEFAULT VALUES RETURNING "id"

b := B{
    As: []A{a1, a2},
}
db.Create(&b)

INSERT INTO "as" ("id") VALUES (3),(4) ON CONFLICT DO NOTHING RETURNING "id"
INSERT INTO "a_bs" ("b_id","a_id") VALUES (3,3),(3,4) ON CONFLICT DO NOTHING
INSERT INTO "bs" DEFAULT VALUES RETURNING "id"

b := B{}
db.Create(&b)
db.Model(&b).Association("As").Append([]A{a1, a2})