main.go

package main

import (
	"database/sql/driver"
	"encoding/json"
	"fmt"
	"time"

	"github.com/jinzhu/gorm"
	_ "github.com/jinzhu/gorm/dialects/postgres"
)

var DB *gorm.DB
var dberr error

type Date struct {
	time.Time
}

type CustomerBroker struct {
	gorm.Model
	StartDate Date `gorm:"type:date,column:start_date" json:"start_date"`
	EndDate   Date `gorm:"type:date,column:end_date" json:"end_date"`
}

func (d *Date) UnmarshalJSON(b []byte) (err error) {
	if b[0] == '"' && b[len(b)-1] == '"' {
		b = b[1 : len(b)-1]
	}

	// take care of null..
	if len(b) == 0 || string(b) == "null" {
		d.Time = time.Time{}
		return
	}

	d.Time, err = time.Parse("2006-01-02", string(b))
	return
}

func (d Date) Scan(b interface{}) (err error) {
	// switch b.(type) {
	// case nil:
	// 	d.Time = time.Time{}
	// case string:
	// 	d.Time, err = time.Parse("2006-01-02", b.(string))
	// }
	return
}

func (d Date) Value() (driver.Value, error) {
	// check if the date was not set..
	if d.Time.IsZero() {
		return nil, nil
	}
	return d.Time.Format("2006-01-02"), nil
}

func init() {
	DB, dberr = gorm.Open("postgres", "host=127.0.0.1 port=5432 user=admin dbname=repl_test sslmode=disable")
	if dberr != nil {
		panic(dberr)
	}
}

func main() {
	record := CustomerBroker{}
	data := []byte(`{"start_date": "2019-05-29", "end_date": null}`)
	err := json.Unmarshal(data, &record)
	if err != nil {
		panic(err)
	}
	DB.Create(&record)
	fmt.Println(DB.Error)
}