How do I unmarshal this JSON array into a struct slice with Go?

Issue

I have a JSON file like this:

[
  {   

    "namespace": "pulsarNamespace1",
    "name": "pulsarFunction1",
    "tenant": "pulsarTenant1"
  },

  {   

    "namespace": "pulsarNamespace2",
    "name": "pulsarFunction2",
    "tenant": "pulsarTenant1"
  }
]

I am attempting to deserialize/unmarshal this JSON array into a slice of structs, but I’m getting structs with empty (default) values.

When I run my code, it correctly reads my file into a string, but it’s not deserializing the data correctly and just writes empty structs to the console, like this:

[]main.Config{main.Config{namespace:””, tenant:””, name:””},
main.Config{namespace:””, tenant:””, name:””}}

Namespace: Name: %!d(string=)

Namespace: Name: %!d(string=)

Here’s my code in Go:

package main

import (
    "encoding/json"
    "fmt"
    "io"
    "io/ioutil"
    "net/http"
    "os"
) 
// Ignore the unused imports.

type Config struct {
    namespace string `json:"namespace,omitempty"`
    tenant    string `json:"tenant,omitempty"`
    name      string `json:"name,omitempty"`
}

func getConfigs() string {
    b, err := ioutil.ReadFile("fastDeploy_example.json") // just pass the file name
    if err != nil {
        fmt.Print(err)
    }
    str := string(b) // convert content to a 'string'
    fmt.Println(str) // print the content as a 'string'
    return str
}

func deserializeJson(configJson string) []Config {
    jsonAsBytes := []byte(configJson)
    configs := make([]Config, 0)
    err := json.Unmarshal(jsonAsBytes, &configs)
    fmt.Printf("%#v\n", configs)
    if err != nil {
        panic(err)
    }
    return configs
}

func main() {
    // Unmarshal each fastDeploy config component into a slice of structs.
    jsonConfigList := getConfigs()
    unmarshelledConfigs := deserializeJson(jsonConfigList)

    for _, configObj := range unmarshelledConfigs {
        fmt.Printf("Namespace: %s Name: %d\n", configObj.namespace, configObj.name)
    }
}

Moreover, if I understand the purpose of using omitempty, then it shouldn’t even be writing the empty fields. However, it appears that it’s writing them anyway.

How do I correctly deserialize/unmarshal my JSON array into my slice of structs in Golang?

Solution

Export the field names of your struct: Namespace, Tenant, Name, etc., so the unmarshaler can set them via reflection.

Re: omitempty, that’s a tag for the json marshaler. If you marshal your struct to json with empty strings, then those fields will be omitted. If you printf the struct, they will be printed.

Answered By – Burak Serdar

Answer Checked By – Clifford M. (GoLangFix Volunteer)

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