周末线上出现一个问题，3月份的订单没有算出来，从数据库表数据上看，订单数据已经是完成状态，但数据为空。
业务上的逻辑是，每天会计算上个月的订单和当月的订单和。一月的订单周期是一个有1日12点到下个月的1日12点。
如前当3月31日，上个月的周期是2月1日12点到3月1日12点；本月的周期是3月1点12到当前时间点。
逻辑在处理上个月的订单时用了 AddDate
lastMonth := time.AddDate(0, -1, 0).Format("200601")
问题就出现在这里。 当前时间是3月31时，time.AddDate(0, -1, 0) 之后，是 20240302 ，还是3月份，并不符合预期。
如下代码：
package main
import (
"fmt"
"time"
)
func main() {
today := time.Date(2024, 2, 29, 0, 0, 0, 0, time.Local)
nextDay := today.AddDate(0, -1, 0)
fmt.Printf("today :%v nextDay :%+v \n", today.Format("20060102"), nextDay.Format("20060102"))
today = time.Date(2024, 3, 31, 0, 0, 0, 0, time.Local)
nextDay = today.AddDate(0, -1, 0)
fmt.Printf("today :%v nextDay :%+v \n", today.Format("20060102"), nextDay.Format("20060102"))
today = time.Date(2024, 4, 30, 0, 0, 0, 0, time.Local)
nextDay = today.AddDate(0, -1, 0)
fmt.Printf("today :%v nextDay :%+v \n", today.Format("20060102"), nextDay.Format("20060102"))
today = time.Date(2024, 5, 31, 0, 0, 0, 0, time.Local)
nextDay = today.AddDate(0, -1, 0)
fmt.Printf("today :%v nextDay :%+v \n", today.Format("20060102"), nextDay.Format("20060102"))
today = time.Date(2024, 6, 30, 0, 0, 0, 0, time.Local)
nextDay = today.AddDate(0, -1, 0)
fmt.Printf("today :%v nextDay :%+v \n", today.Format("20060102"), nextDay.Format("20060102"))
today = time.Date(2024, 7, 31, 0, 0, 0, 0, time.Local)
nextDay = today.AddDate(0, -1, 0)
fmt.Printf("today :%v nextDay :%+v \n", today.Format("20060102"), nextDay.Format("20060102"))
today = time.Date(2024, 8, 31, 0, 0, 0, 0, time.Local)
nextDay = today.AddDate(0, -1, 0)
fmt.Printf("today :%v nextDay :%+v \n", today.Format("20060102"), nextDay.Format("20060102"))
today = time.Date(2024, 9, 30, 0, 0, 0, 0, time.Local)
nextDay = today.AddDate(0, -1, 0)
fmt.Printf("today :%v nextDay :%+v \n", today.Format("20060102"), nextDay.Format("20060102"))
today = time.Date(2024, 10, 31, 0, 0, 0, 0, time.Local)
nextDay = today.AddDate(0, -1, 0)
fmt.Printf("today :%v nextDay :%+v \n", today.Format("20060102"), nextDay.Format("20060102"))
today = time.Date(2024, 11, 30, 0, 0, 0, 0, time.Local)
nextDay = today.AddDate(0, -1, 0)
fmt.Printf("today :%v nextDay :%+v \n", today.Format("20060102"), nextDay.Format("20060102"))
today = time.Date(2024, 12, 31, 0, 0, 0, 0, time.Local)
nextDay = today.AddDate(0, -1, 0)
fmt.Printf("today :%v nextDay :%+v \n", today.Format("20060102"), nextDay.Format("20060102"))
}
输出：
today :20240229 nextDay :20240129
today :20240331 nextDay :20240302
today :20240430 nextDay :20240330
today :20240531 nextDay :20240501
today :20240630 nextDay :20240530
today :20240731 nextDay :20240701
today :20240831 nextDay :20240731
today :20240930 nextDay :20240830
today :20241031 nextDay :20241001
today :20241130 nextDay :20241030
today :20241231 nextDay :20241201
其中，如 20240331、20240531、20240731、20241031 这一些时算的上月时间就出错，它依然是本月的时间。
解决这个问题最简单，最快的方式是引用库 https://github.com/Andrew-M-C/go.timeconv
package main
import (
"fmt"
"time"
"github.com/Andrew-M-C/go.timeconv"
)
func main() {
t := time.Date(2019, 1, 31, 0, 0, 0, 0, time.UTC)
nt := t.AddDate(0, 1, 0) // Add one month
fmt.Printf("%v\n", nt) // 2019-03-03 00:00:00 +0000 UTC, not expected
nt = timeconv.AddDate(t, 0, 1, 0)
fmt.Printf("%v\n", nt) // 2019-02-28 00:00:00 +0000 UTC
}
1、令人困惑的 Go time.AddDate https://learnku.com/articles/71760
2、Go time 包中的 AddDate 的逻辑避坑指南 https://cloud.tencent.com/developer/article/1803695