Golang中omitempty的作用

前言

Talk is cheap. Show me the code.

TestNotOmitEmpty

TestOmitEmptyWithDefaultValue

testOmitEmptyWithDefaultValueButFatherSet

testOmitEmptyWithNotDefaultValueButFatherSet

前言

在尝试将结构体序列化为 Json 时，你可能会遇到 “omitempty” 标记，本小记就来浅看一下它如何起作用。

先上结论：

基本类型的默认值会被 omit，除了数组。

指针类型为 nil 时会被 omit。

Talk is cheap. Show me the code.

package main
import (
   "encoding/json"
   "errors"
   "fmt"
)
type TestNotOmitEmpty struct {
   Uint8   uint8   `json:"uint8"`
   Uint16  uint16  `json:"uint16"`
   Uint32  uint32  `json:"uint32"`
   Uint64  uint64  `json:"uint64"`
   Int8    int8    `json:"int8"`
   Int16   int16   `json:"int16"`
   Int32   int32   `json:"int32"`
   Int64   int64   `json:"int64"`
   Int     int     `json:"int"`
   Float32 float32 `json:"float32"`
   Float64 float64 `json:"float64"`
   // Complex64     complex64      `json:"complex64"` // json: unsupported type
   // Complex128    complex128     `json:"complex128"` // json: unsupported type
   Byte          byte           `json:"byte"`
   Rune          rune           `json:"rune"`
   Uintptr       uintptr        `json:"uintptr"`
   String        string         `json:"string"`
   StringPointer *string        `json:"stringPointer"`
   Array         [10]int        `json:"array"`
   Slice         []int          `json:"slice"`
   Map           map[int]string `json:"map"`
   // Channel       chan int       `json:"channel"` // json: unsupported type
   Interface interface{} `json:"interface"`
   Error     error       `json:"error"`
}
type TestOmitEmptyWithDefaultValue struct {
   Uint8   uint8   `json:"uint8,omitempty"`
   Uint16  uint16  `json:"uint16,omitempty"`
   Uint32  uint32  `json:"uint32,omitempty"`
   Uint64  uint64  `json:"uint64,omitempty"`
   Int8    int8    `json:"int8,omitempty"`
   Int16   int16   `json:"int16,omitempty"`
   Int32   int32   `json:"int32,omitempty"`
   Int64   int64   `json:"int64,omitempty"`
   Int     int     `json:"int,omitempty"`
   Float32 float32 `json:"float32,omitempty"`
   Float64 float64 `json:"float64,omitempty"`
   // Complex64     complex64      `json:"complex64,omitempty"` // json: unsupported type
   // Complex128    complex128     `json:"complex128,omitempty"` // json: unsupported type
   Byte          byte           `json:"byte,omitempty"`
   Rune          rune           `json:"rune,omitempty"`
   Uintptr       uintptr        `json:"uintptr,omitempty"`
   String        string         `json:"string,omitempty"`
   StringPointer *string        `json:"stringPointer,omitempty"`
   Array         [10]int        `json:"array,omitempty"`
   Slice         []int          `json:"slice,omitempty"`
   Map           map[int]string `json:"map,omitempty"`
   // Channel       chan int       `json:"channel,omitempty"` // json: unsupported type
   Interface interface{} `json:"interface,omitempty"`
   Error     error       `json:"error,omitempty"`
}
func ToStringPointer(s string) *string {
   return &s
}
func main() {
   testOmitEmpty := TestNotOmitEmpty{}
   jsonData, err := json.Marshal(testOmitEmpty)
   if err != nil {
      println(err)
      panic(err)
   }
   fmt.Printf("TestNotOmitEmpty: %s\n", jsonData)
   testOmitEmptyWithDefaultValue := TestOmitEmptyWithDefaultValue{}
   jsonData2, err := json.Marshal(testOmitEmptyWithDefaultValue)
   if err != nil {
      println(err)
      panic(err)
   }
   fmt.Printf("TestOmitEmptyWithDefaultValue: %s\n", jsonData2)
   testOmitEmptyWithDefaultValueButFatherSet := TestOmitEmptyWithDefaultValue{
      Uint8:         0,
      Uint16:        0,
      Uint32:        0,
      Uint64:        0,
      Int8:          0,
      Int16:         0,
      Int32:         0,
      Int64:         0,
      Int:           0,
      Float32:       0,
      Float64:       0,
      Byte:          0,
      Rune:          0,
      Uintptr:       0,
      String:        "",
      StringPointer: nil,
      Array:         [10]int{},
      Slice:         nil,
      Map:           nil,
      Interface:     nil,
      Error:         nil,
   }
   jsonData3, err := json.Marshal(testOmitEmptyWithDefaultValueButFatherSet)
   if err != nil {
      println(err)
      panic(err)
   }
   fmt.Printf("testOmitEmptyWithDefaultValueButFatherSet: %s\n", jsonData3)
   testOmitEmptyWithNotDefaultValueButFatherSet := TestOmitEmptyWithDefaultValue{
      Uint8:         1,
      Uint16:        1,
      Uint32:        1,
      Uint64:        1,
      Int8:          1,
      Int16:         1,
      Int32:         1,
      Int64:         1,
      Int:           1,
      Float32:       1,
      Float64:       1,
      Byte:          1,
      Rune:          1,
      Uintptr:       1,
      String:        "1",
      StringPointer: ToStringPointer(""),
      Array:         [10]int{1},
      Slice:         []int{1},
      Map:           map[int]string{1: "1"},
      Interface:     "1",
      Error:         errors.New("error"),
   }
   jsonData4, err := json.Marshal(testOmitEmptyWithNotDefaultValueButFatherSet)
   if err != nil {
      println(err)
      panic(err)
   }
   fmt.Printf("testOmitEmptyWithNotDefaultValueButFatherSet: %s\n", jsonData4)
}

TestNotOmitEmpty

全部序列化成功。