copier

開源倉庫：jinzhu/copier: Copier for golang, copy value from struct to struct and more (github.com)

文檔地址：jinzhu/copier: Copier for golang, copy value from struct to struct and more (github.com)

copier 是一個用於在 go 中進行類型復制的庫，多用於結構體之間的轉換。作者和 gorm 是同一個，它具有以下特點

• 深拷貝
• 復制同名的字段
• 復制切片
• 復制 map
• 復制方法

由於 copier 的復制依賴於反射，所以性能上會有一定的損失。一般這種類型復制的庫分成兩類，一類基於反射，也是就 copier 這種，另一類是基於代碼生成，通過生成類型轉換的代碼，這種方法性能不會造成損失，類似實現的庫有jmattheis/goverter。

安裝

 go get github.com/jinzhu/copier

使用

這個庫使用起來非常簡單，但卻非常的實用。它只對外暴露兩個函數，一個是copier.Copy。

func Copy(toValue interface{}, fromValue interface{}) (err error)

另一個是copier.CopyWithOption，後者可以對復制行為進行一些自定義的配置，在默認情況下不會進行深拷貝。

type Option struct {
  IgnoreEmpty   bool
  CaseSensitive bool
  DeepCopy      bool
  FieldNameMapping []FieldNameMapping
}

func CopyWithOption(toValue interface{}, fromValue interface{}, opt Option) (err error)

下面演示一個不同類型結構體轉換的例子，其中的User和Student結構體是兩個完全不同的類型，沒有任何的關聯。

type User struct {
  Id   string
  Name string
  // 當作為目標結構體時，忽略該字段
  Address string `copier:"-"`
}

type Student struct {
  // 指定字段名
  StudentId   string `copier:"Id"`
  StudentName string `copier:"Name"`
  Address     string
  School      string
  Class       string
}

func main() {
  student := Student{
    StudentId:   "123",
    StudentName: "jack",
    Address:     "usa",
    School:      "MIT",
    Class:       "AI",
  }
  user := User{}
  if err := copier.Copy(&user, &student); err != nil {
    panic(err)
  }
  fmt.Printf("%+v\n", student)
  fmt.Printf("%+v\n", user)
}

輸出

{StudentId:123 StudentName:jack Address:usa School:MIT Class:AI}
{Id:123 Name:jack Address:}

下面看復制切片

func main() {
  student := []Student{
    {
      StudentId:   "123",
      StudentName: "jack",
      Address:     "usa",
      School:      "MIT",
      Class:       "AI",
    },
    {
      StudentId:   "123",
      StudentName: "jack",
      Address:     "usa",
      School:      "MIT",
      Class:       "AI",
    },
  }

  var user []User
  if err := copier.Copy(&user, &student); err != nil {
    panic(err)
  }
  fmt.Printf("%+v\n", student)
  fmt.Printf("%+v\n", user)
}

輸出

[{StudentId:123 StudentName:jack Address:usa School:MIT Class:AI} {StudentId:123 StudentName:jack Address:usa School:MIT Class:AI}]
[{Id:123 Name:jack Address:} {Id:123 Name:jack Address:}]

復制 map

type User struct {
  Id   string
  Name string
  // 當作為目標結構體時，忽略該字段
  Address string `copier:"-"`
}

type Student struct {
  // 指定字段名
  StudentId   string `copier:"Id"`
  StudentName string `copier:"Name"`
  Address     string
  School      string
  Class       string
}

func main() {
  student := Student{
    StudentId:   "123",
    StudentName: "jack",
    Address:     "usa",
    School:      "MIT",
    Class:       "AI",
  }

  src := make(map[string]Student)
  src["a"] = student
  src["b"] = student

  dest := make(map[string]User)

  if err := copier.Copy(&dest, &src); err != nil {
    panic(err)
  }
  fmt.Printf("%+v\n", src)
  fmt.Printf("%+v\n", dest)
}

輸出

map[a:{StudentId:123 StudentName:jack Address:usa School:MIT Class:AI} b:{StudentId:123 StudentName:jack Address:usa School:MIT Class:AI}]
map[a:{Id:123 Name:jack Address:} b:{Id:123 Name:jack Address:}]

自定義

還可以自定義轉換方法，只需要傳入copier.TypeConverter即可

type TypeConverter struct {
  SrcType interface{}
  DstType interface{}
  Fn      func(src interface{}) (dst interface{}, err error)
}

如下所示

type User struct {
  Id   string
  Name string
  // 當作為目標結構體時，忽略該字段
  Address string `copier:"-"`
}

type Student struct {
  // 指定字段名
  StudentId   string `copier:"Id"`
  StudentName string `copier:"Name"`
  Address     string
  School      string
  Class       string
}

func main() {
  student := Student{
    StudentId:   "123",
    StudentName: "jack",
    Address:     "usa",
    School:      "MIT",
    Class:       "AI",
  }

  src := make(map[string]Student)
  src["a"] = student
  src["b"] = student

  dest := make(map[string]User)

  if err := copier.CopyWithOption(&dest, &src, copier.Option{
    IgnoreEmpty:   false,
    CaseSensitive: false,
    DeepCopy:      false,
    Converters: []copier.TypeConverter{
      {
        SrcType: Student{},
        DstType: User{},
        Fn: func(src interface{}) (dst interface{}, err error) {
          s, ok := src.(Student)
          if !ok {
            return User{}, errors.New("error type")
          }
          return User{
            Id: s.StudentId,
          }, nil
        },
      },
    },
    FieldNameMapping: nil,
  }); err != nil {
    panic(err)
  }
  fmt.Printf("%+v\n", src)
  fmt.Printf("%+v\n", dest)
}

輸出

map[a:{StudentId:123 StudentName:jack Address:usa School:MIT Class:AI} b:{StudentId:123 StudentName:jack Address:usa School:MIT Class:AI}]
map[a:{Id:123 Name: Address:} b:{Id:123 Name: Address:}]