Allow modification of null values

[enzofoucaud]

Describe the feature

Allow me to updates non zero value

Motivation

map[string]interface{} is complicated to use when you have complex structures like :

type Component struct {
	gorm.Model
	FamilyID               uint
	Name                   string
        ...

	// Relationships
	1 []1 `gorm:"ForeignKey:ComponentID;constraint:OnUpdate:CASCADE"`
	2 []2 `gorm:"ForeignKey:ComponentID;constraint:OnUpdate:CASCADE"`
	3 []3 `gorm:"ForeignKey:ComponentID;constraint:OnUpdate:CASCADE"`
	4 []4 `gorm:"ForeignKey:ComponentID;constraint:OnUpdate:CASCADE"`
	5 []5 `gorm:"ForeignKey:ComponentID;constraint:OnUpdate:CASCADE"`
        ...

	// Relationships others
	10 []10 `gorm:"ForeignKey:ComponentID;constraint:OnUpdate:CASCADE"`
	11 []11 `gorm:"ForeignKey:ComponentID;constraint:OnUpdate:CASCADE"`
}

Related Issues

#3901

Description

maybe add :

• gorm:"allowzero"

maybe fix :

• Select(*) before Update or Updates