42. Go - JSON

Marshalling (Turning struct types into JSON format:

Code Example:
// marshall function takes anything and returns a slice of bytes
package main

import (
    "encoding/json"
    "fmt"
    "os"
)

type serverInfo struct {
    ID      int
    Name    string
    IsNew   bool
    Members []string
}

func main() {
    serverOne := serverInfo{
        ID:      0,
        Name:    "Crimson",
        IsNew:   false,
        Members: []string{"Bob", "Ada"},
    }

    marshall, err := json.Marshal(serverOne)
    if err != nil {
        fmt.Println(err)
    }

    fmt.Println(marshall) // not correct format print

    os.Stdout.Write(marshall) // write output
}



Un-Marshalling (Decoding a JSON format, which is a array of bytes for GO.
// unmarshall function takes a slice of byte and interface and returns an error. Takes decoded JSON and stores it at address given by interface.
Code Example:
package main

import (
    "encoding/json"
    "fmt"
    "os"
)

type serverInfo struct {
    ID      int
    Name    string
    IsNew   bool
    Members []string
}

func main() {
    serverOne := serverInfo{
        ID:      0,
        Name:    "Crimson",
        IsNew:   false,
        Members: []string{"Bob", "Ada"},
    }

    testTable := []serverInfo{serverOne}

    marshaled, err := json.Marshal(testTable)
    if err != nil {
        fmt.Println(err)
    }

    fmt.Println(marshaled) // not correct format print

    os.Stdout.Write(marshaled) // write output
    fmt.Println("B")

    var servers []serverInfo
    unmarshaled := json.Unmarshal(marshaled, &servers)
    if unmarshaled != nil {
        fmt.Println(err)
    }

    fmt.Println(servers, "A")
}



Unmarshalling JSON by creating a type struct with JSON tags:
// need to define the structure of the JSON with a struct and JSON tags, struct vars must match tags

Code Example:
package main

import (
    "encoding/json"
    "fmt"
)

type serverInfo struct {
    ID      int      `json:"ID"`
    Name    string   `json:"Name"`
    IsNew   bool     `json:"IsNew"`
    Members []string `json:"Members"`
}

func main() {
    jsonString := `[{"ID":0,"Name":"Crimson","IsNew":false,"Members":["Bob","Ada"]}]`
    jsonBytes := []byte(jsonString)

    var serverList []serverInfo
    err := json.Unmarshal(jsonBytes, &serverList)
    if err != nil {
        fmt.Println(err)
    }

    fmt.Println(serverList)
    fmt.Println(serverList[0], "index one")
    fmt.Println(serverList[0].ID, "Index 1: ID")
    fmt.Println(serverList[0].Name, "Index 1: Name")
    fmt.Println(serverList[0].IsNew, "Index 1: IsNew")
    fmt.Println(serverList[0].Members, "Index 1: Members")
    fmt.Println(serverList[0].Members[1], "Index 1: Members[1]")
}


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