ReferenceSchema *Schema
	References      []*Field
	OnDelete        string
	OnUpdate        string
}

func (constraint *Constraint) GetName() string { return constraint.Name }

func (constraint *Constraint) Build() (sql string, vars []interface{}) {
	sql = "CONSTRAINT ? FOREIGN KEY ? REFERENCES ??"
	if constraint.OnDelete != "" {
		sql += " ON DELETE " + constraint.OnDelete
	}

	if constraint.OnUpdate != "" {