###### tags: `Golang Package`

# Diff
[github](https://github.com/r3labs/diff)

比較兩個相同類型的結構，並回傳所有修改處。

## Usecase 1

	from := &Item{
		ID:     "1293120938",
		Price:  2000,
		Look:   22,
		Status: true,
	}
	to := &Item{
		ID:     "1293120938",
		Price:  1500,
		Look:   30,
		Status: true,
	}

	changelog, _ := diff.Diff(from, to)

結果中列出
Price 2000 -> 1500
Look 22 -> 30

 (diff.Changelog) (len=2 cap=2) {
 (diff.Change) {
  Type: (string) (len=6) "update",
  Path: ([]string) (len=1 cap=1) {
   (string) (len=5) "Price"
  },
  From: (int64) 2000,
  To: (int64) 1500
 },
 (diff.Change) {
  Type: (string) (len=6) "update",
  Path: ([]string) (len=1 cap=1) {
   (string) (len=4) "Look"
  },
  From: (int64) 22,
  To: (int64) 30
 }
}

## Usecase 2
子結構

from := &Item{
		ID:     "1293120938",
		Price:  2000,
		Look:   22,
		Status: true,
		Buyer: &Member{
			Name: "Mask",
			Age:  20,
		},
	}
	to := &Item{
		ID:     "1293120938",
		Price:  2000,
		Look:   22,
		Status: true,
		Buyer: &Member{
			Name: "Krotos",
			Age:  20,
		},
	}

	changelog, _ := diff.Diff(from, to)

返回的結構中指出Buyer、Name

(diff.Changelog) (len=1 cap=1) {
 (diff.Change) {
  Type: (string) (len=6) "update",
  Path: ([]string) (len=2 cap=2) {
   (string) (len=5) "Buyer",
   (string) (len=4) "Name"
  },
  From: (string) (len=4) "Mask",
  To: (string) (len=6) "Krotos"
 }
}

## Usecase 3
將變更的內容更改回from

from := &Item{
		ID:     "1293120938",
		Price:  2000,
		Look:   22,
		Status: true,
		Buyer: &Member{
			Name: "Mask",
			Age:  20,
		},
		Tag:      []int{},
		CreateAt: time.Now(),
	}

	to := &Item{
		ID:     "1293120938",
		Price:  2000,
		Look:   33,
		Status: true,
		Buyer: &Member{
			Name: "krotos",
			Age:  30,
		},
		Tag: []int{1, 2, 3, 4, 5, 8},
	}

	changelog, _ := diff.Diff(from, to, diff.AllowTypeMismatch(true))
	diff.Patch(changelog, &from)
	spew.Dump(from)

(*main.Item)(0xc0000b0240)({
 ID: (string) (len=10) "1293120938",
 Price: (int64) 2000,
 Look: (int64) 33,
 Status: (bool) true,
 Buyer: (*main.Member)(0xc0000aa160)({
  Name: (string) (len=6) "krotos",
  Age: (int) 30
 }),
 Tag: ([]int) (len=6 cap=8) {
  (int) 1,
  (int) 2,
  (int) 3,
  (int) 4,
  (int) 5,
  (int) 8
 },
 CreateAt: (time.Time) 2021-12-16 16:21:25.311424 +0800 CST m=+0.000324751
})

# 結論
原先是想說可以運用在Update上，但是沒傳得值會被當作要更新成空的，運用上限制比較多，可能沒有那麼好用，但如果能用上，可以省去一個欄位一個欄位更改的工。

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