Parse JSON with an array in golang

Question

I would like to retrieve all IDs and also the index value.

{
  "results": [
    {
      "ID": "3b72"
    },
    {
      "ID": "d953b1"
    },
    {
      "ID": "8eac"
    },
    {
      "ID": "00b4c"
    },
    {
      "ID": "22360"
    }
  ],
  "index": 10
}

I tried the following but no success ( I am quite new in golang):

var result map[string]interface{}
json.Unmarshal([]byte(body), &result)

ids:= result["results"].(map[string]interface{})

for key, value := range ids{
    fmt.Println(key, value.(string))
}

@Sammy btw, please approve the correct and best answer, because it might be useful for others. They probably face similar problem and doesn't know how to solve it. see more stackoverflow.com/help/someone-answers — novalagung
– novalagung, Commented Oct 15, 2018 at 8:28
Btw there is proably not the correct and best answer, this would imply that any other way would be false which isn't. Better also means readable and maintainable which obviously is better using structs instead of random type casts. — danopz
– danopz, Commented Oct 15, 2018 at 13:04
The question was not about unmarshalling JSON into a struct. Both answers are valid, but there might be a reason OP is using unmarshalling into a map - there's always a possibility that JSON structure is not fixed. That's why I voted for @xpare answer, which exactly answers the question without refactoring and assumptions. However, perfect answer would probably suggest an option of unmarshalling into a struct for convenience, and explain pros and cons of this approach. — Andrejs Cainikovs
– Andrejs Cainikovs, Commented Oct 15, 2018 at 15:50
@danopz btw, I was not trying to say that that my answer is the correct and the best one indeed. I'm just telling OP to approve the best answer from his perspective, and letting him know about the guidelines. because yesterday I saw his profile, I found out that he's rarely approve people answer on his own questions. — novalagung
– novalagung, Commented Oct 16, 2018 at 2:39

novalagung · Accepted Answer · 2018-10-16 00:14:57Z

4

As per your json string, few things need to be fixed. First, the result["results"] property need to be casted as []interface{} because results hold an array data.

ids := result["results"].([]interface{})

Then, on each iteration of ids, variable value (whose type is interface{}) need to be casted into map[string]interface{}, so we will be able to access ID property to get it's value.

for index, value := range ids {
    valueMap := value.(map[string]interface{})
    fmt.Println(index, valueMap["ID"])
}

Working example: https://play.golang.org/p/Pxq6u7q-NAK

As per @Andrejs' answer, if your JSON structure is fixed, then it would be better to use well defined struct on the result (see @danopz's answer). It has better performance and consume less effort interact with it's child.

edited Oct 16, 2018 at 0:14

answered Oct 15, 2018 at 8:13

novalagung

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Comments

danopz · Accepted Answer · 2018-10-15 13:06:40Z

1

You should probably define a struct for the body and unmarshal into this:

var result struct {
    Results []struct{
        ID string `json:"ID"`
    } `json:"results"`
    Index int `json:"index"`
}

err := json.Unmarshal(body, &result)

if err != nil {
    // do something, result may be empty
    return
}

for i, result := range result.Results {
    fmt.Println(i, result.ID)
}

Then you would have access to the values e.g. by calling result.Index or result.Results[0].ID.

Working example: https://play.golang.org/p/j1WpEolQlXV

edited Oct 15, 2018 at 13:06

answered Oct 15, 2018 at 8:12

danopz

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