JSON and Data Exchange

Optional Fields

Optional JSON fields can be included only when a value is present.

optional field An optional JSON field can be present for one value and absent for another while the Go type stays the same.

Optional Fields

includeEmail
optional_fields.go
Replay: real traced execution (multi-file project)
package main

import (
	"fmt"
	"strings"
)

type Profile struct {
	Name  string `json:"name"`
	Email string `json:"email,omitempty"`
}

func main() {
	var includeEmail = true
	profile := Profile{Name: "Mina"}

	if includeEmail {
		profile.Email = "mina@example.com"
	}

	text := `{"name":"` + profile.Name + `"}`
	if profile.Email != "" {
		text = `{"name":"` + profile.Name + `","email":"` + profile.Email + `"}`
	}

	hasEmail := strings.Contains(text, "email")
	fmt.Println("includeEmail=", includeEmail)
	fmt.Println("hasEmail=", hasEmail)
	fmt.Println("json=", text)
}

package main

import (
	"fmt"
	"strings"
)

type Profile struct {
	Name  string `json:"name"`
	Email string `json:"email,omitempty"`
}

func main() {
	var includeEmail = false
	profile := Profile{Name: "Mina"}

	if includeEmail {
		profile.Email = "mina@example.com"
	}

	text := `{"name":"` + profile.Name + `"}`
	if profile.Email != "" {
		text = `{"name":"` + profile.Name + `","email":"` + profile.Email + `"}`
	}

	hasEmail := strings.Contains(text, "email")
	fmt.Println("includeEmail=", includeEmail)
	fmt.Println("hasEmail=", hasEmail)
	fmt.Println("json=", text)
}

  1. includeEmail ← true, profile ← main.Profile{Name:"Mina", Email:""}

    13func main() {14  var includeEmail→ true = true //@includeEmail=false15  profile→ main.Profile{Name:"Mina", Email:""} := Profile{Name: "Mina"}

  2. profile.Email ← "mina@example.com"

    17if includeEmailtrue {18  profile.Email→ "mina@example.com" = "mina@example.com"19}

  3. text ← "{\"name\":\"Mina\"}"

    21text→ "{\"name\":\"Mina\"}" := `{"name":"` + profile.Name"Mina" + `"}`22if profile.Email != "" {

  4. text ← "{\"name\":\"Mina\",\"email\":\"mina@example.com\"}"

    21text := `{"name":"` + profile.Name + `"}`22if profile.Email"mina@example.com" != "" {23  text→ "{\"name\":\"Mina\",\"email\":\"mina@example.com\"}" = `{"name":"` + profile.Name"Mina" + `","email":"` + profile.Email"mina@example.com" + `"}`24}

  5. hasEmail ← true

    26  hasEmail→ true := strings.Contains(text"{\"name\":\"Mina\",\"email\":\"mina@example.com\"}", "email")27  fmt.Println("includeEmail=", includeEmailtrue)28  fmt.Println("hasEmail=", hasEmailtrue)29  fmt.Println("json=", text"{\"name\":\"Mina\",\"email\":\"mina@example.com\"}")30}
    outputincludeEmail= true
hasEmail= true
json= {"name":"Mina","email":"mina@example.com"}

  1. includeEmail ← false, profile ← main.Profile{Name:"Mina", Email:""}

    13func main() {14  var includeEmail→ false = false15  profile→ main.Profile{Name:"Mina", Email:""} := Profile{Name: "Mina"}1617  if includeEmail {18    profile.Email = "mina@example.com"19  }2021  text→ "{\"name\":\"Mina\"}" := `{"name":"` + profile.Name"Mina" + `"}`22  if profile.Email != "" {23    text = `{"name":"` + profile.Name + `","email":"` + profile.Email + `"}`24  }2526  hasEmail→ false := strings.Contains(text"{\"name\":\"Mina\"}", "email")27  fmt.Println("includeEmail=", includeEmailfalse)28  fmt.Println("hasEmail=", hasEmailfalse)29  fmt.Println("json=", text"{\"name\":\"Mina\"}")30}
    outputincludeEmail= false
hasEmail= false
json= {"name":"Mina"}