Extracting a deeply nested JSON array from a document

Question

Extracting a deeply nested JSON array from a document

After finding a JSON file named sample.json, I discovered that it contains an array of JSON objects with timestamps, extra data IDs, and event information. Here's a snippet:

[
{
  "time": "2021-01-04T00:11:32.362Z",
  "extra_data": {
    "id": "123"
  },
  "info": "event123"
},
{
  "time": "2021-01-05T00:11:32.362Z",
  "extra_data": {
    "id": "456"
  },
  "info": "event456"
},
{
  "time": "2021-01-06T00:11:32.362Z",
  "extra_data": {
    "id": "789"
  },
  "info": "event789"
}
]

To unmarshal this JSON array effectively, allowing access to the ID and info for each event, I have crafted the following solution:

func main() {

    file, err := ioutil.ReadFile("/Users/janedoe/Downloads/sample.json")
    var events Event
    json.Unmarshal([]byte(file), &events)
    fmt.Println(reflect.TypeOf(events))
    // Accessing values by keys for each event
    fmt.Println("Event123_Time :", events.Timestamp,
            "\nEvent123_ExtraData_Id :", events.ExtraData.Id,
            "\nEvent123_Info :", events.Info)
} 
type Event struct {
    Time string `json:"time"`
    ExtraData ExtraData `json:"extra_data"`
    Info string `json:"info"`
}

type ExtraData struct {
     Id string   `json:"id"`
}

The current output does not display any values, indicating an issue with the marshalling process. How can I rectify this?

json go marshalling unmarshalling

Answer 1

Answer №1

For working with a JSON array, you should declare the variable as an array too:

var events []Event

Instead of just declaring it as a single Event like this:

var events Event

Below is an updated version incorporating this change:

func main() {
    file, err := ioutil.ReadFile("/Users/janedoe/Downloads/sample.json")
    if err != nil {
        panic(err)
    }
    var events []Event
    if err := json.Unmarshal([]byte(file), &events); err != nil {
        panic(err)
    }
    fmt.Println(reflect.TypeOf(events))
    for i, event := range events {
        // Accessing values by keys for each event
        fmt.Println(i, "Event123_Time :", event.Time,
            "\nEvent123_ExtraData_Id :", event.ExtraData.Id,
            "\nEvent123_Info :", event.Info)
    }
}

type Event struct {
    Time      string    `json:"time"`
    ExtraData ExtraData `json:"extra_data"`
    Info      string    `json:"info"`
}

type ExtraData struct {
    Id string `json:"id"`
}

Answer 2

For working with a JSON array, you should declare the variable as an array too:

var events []Event

Instead of just declaring it as a single Event like this:

var events Event

Below is an updated version incorporating this change:

func main() {
    file, err := ioutil.ReadFile("/Users/janedoe/Downloads/sample.json")
    if err != nil {
        panic(err)
    }
    var events []Event
    if err := json.Unmarshal([]byte(file), &events); err != nil {
        panic(err)
    }
    fmt.Println(reflect.TypeOf(events))
    for i, event := range events {
        // Accessing values by keys for each event
        fmt.Println(i, "Event123_Time :", event.Time,
            "\nEvent123_ExtraData_Id :", event.ExtraData.Id,
            "\nEvent123_Info :", event.Info)
    }
}

type Event struct {
    Time      string    `json:"time"`
    ExtraData ExtraData `json:"extra_data"`
    Info      string    `json:"info"`
}

type ExtraData struct {
    Id string `json:"id"`
}

Extracting a deeply nested JSON array from a document

Answer №1

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