Golang interface conversion error when trying to iterate through map of json array

Question

I'm having an issue when I'm try to iterate through a map of some json.

The original JSON data looks like this:

"dataArray": [
    {
      "name": "default",
      "url": "/some/url"
    },
    {
      "name": "second",
      "url": "/another/url"
    }
]

the map looks like this:

[map[name:default url:/some/url] map[name:second url:/another/url]]

The code looks like this:

for _, urlItem := range item.(map[string]interface{}){
   do some stuff
}

This normally works when it's a JSON object, but this is an array in the JSON and I get the following error:

panic: interface conversion: interface {} is []interface {}, not map[string]interface {}

Any help would be greatly appreciated

Why not just tag some structs and Unmarshal the JSON the sane way? — RayfenWindspear
– RayfenWindspear, Commented Mar 30, 2017 at 15:39
I would, but sometimes the data is there and other times it isn't so I need to test the data before it goes in. It's a pain, but if there is no data to go in an array then the field that holds the array doesn't exist. — Paul A.T. Wilson
– Paul A.T. Wilson, Commented Mar 30, 2017 at 15:47
You mean the field in the JSON doesn't exist? You can just check for nil in that case. — RayfenWindspear
– RayfenWindspear, Commented Mar 30, 2017 at 15:55

Gujarat Santana · Accepted Answer · 2017-03-30 15:30:56Z

5

The error is :

panic: interface conversion: interface {} is []interface {}, not map[string]interface {}

in your code you're converting item into map[string]interface{} :

for _, urlItem := range item.(map[string]interface{}){
   do some stuff
}

But the actual item is []interface {} : change your covert type to this.

Because as you can see your result data is :

[map[name:default url:/some/url] map[name:second url:/another/url]]

it is an array that has map. not map.

First you can convert your data to []interface{} and then get the index of that and convert it to map[string]interface{}. so an example will look like this :

data := item.([]interface{})
for _,value := range data{
  yourMap := value.(map[string]interface{})
  //name value
  name := yourMap["name"].(string) // and so on
}

edited Mar 30, 2017 at 15:30

answered Mar 30, 2017 at 15:23

Gujarat Santana

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