how to access nested Json key values in Golang

Question

Team, new to Programming. I have data available after unmarshaling the Json as shown below, which has nested Key values. flat key values I am able to access, how do I access nested key values. Here is the byte slice data shown below after unmarshaling —>

tables:[map[name:basic__snatpool_members] map[name:net__snatpool_members] map[name:optimizations__hosts] map[columnNames:[name] name:pool__hosts rows:[map[row:[ry.hj.com]]]] traffic_group:/Common/traffic-group-1

Flat key values I am able to access by using the following code

p.TrafficGroup = m[“traffic_group”].(string)

here is the complete function

func dataToIapp(name string, d *schema.ResourceData) bigip.Iapp {
        var p bigip.Iapp

        var obj interface{}

        jsonblob := []byte(d.Get("jsonfile").(string))
        err := json.Unmarshal(jsonblob, &obj)
        if err != nil {
                fmt.Println("error", err)
        }
        m := obj.(map[string]interface{}) // Important: to access property
        p.Name = m[“name”].(string)
        p.Partition = m[“partition”].(string)

        p.InheritedDevicegroup = m[“inherited_devicegroup”].(string)

}

Please show the raw JSON, and the definition of Iapp. If you know the JSON structure in advance, it's more common to unmarshal directly into a structure. See here. — Mark
– Mark, Commented Jan 22, 2018 at 19:46

Jacob Lambert · Accepted Answer · 2018-01-22 20:17:12Z

Note: This may not work with your JSON structure. I inferred what it would be based on your question but without the actual structure, I cannot guarantee this to work without modification.

If you want to access them in a map, you need to assert that the interface pulled from the first map is actually a map. So you would need to do this:

tmp := m["tables"]
tables, ok := tmp.(map[string]string)
if !ok {
    //error handling here
}

r.Name = tables["name"].(string)

But instead of accessing the unmarshaled JSON as a map[string]interface{}, why don't you create structs that match your JSON output?

type JSONRoot struct {
    Name string `json:"name"`
    Partition string `json:"partition"`
    InheritedDevicegroup string `json:"inherited_devicegroup"`
    Tables map[string]string `json:"tables"` //Ideally, this would be a map of structs
}

Then in your code:

func dataToIapp(name string, d *schema.ResourceData) bigip.Iapp {
    var p bigip.Iapp

    var obj &JSONRoot{}

    jsonblob := []byte(d.Get("jsonfile").(string))
    err := json.Unmarshal(jsonblob, &obj)
    if err != nil {
            fmt.Println("error", err)
    }

    p.Name = obj.Name
    p.Partition = obj.Partition

    p.InheritedDevicegroup = obj.InheritedDevicegroup

    p.Name = obj.Tables["name"]
}

mkopriva · Accepted Answer · 2018-01-22 21:09:23Z

JSON objects are unmarshaled into map[string]interface{}, JSON arrays into []interface{}, same applies for nested objects/arrays.

So for example if a key/index maps to a nested object you need to type assert the value to map[string]interface{} and if the key/index maps to an array of objects you first need to assert the value to []interface{} and then each element to map[string]interface{}.

e.g. (for brevity this code is not guarding against panic)

tables := obj.(map[string]interface{})["tables"]
table1 := tables.([]interface{})[0]
name := table1.(map[string]interface{})["name"]
namestr := name.(string)

However, if it's the case that the json you are parsing is not dynamic but instead has a specific structure you should define a struct type that mirrors that structure and unmarshal the json into that.

Pandemonium · Accepted Answer · 2018-01-22 22:58:44Z

0

All you have to do is repeatedly accessing the map via type-switching or assertion:

for _, table := range m["tables"] {
    switch val := table {
        case string:
                fmt.Println("table is string")
        case int:
                fmt.Println("table is integer")

        // This is your case, since JSON is unmarshaled to type []interface{} and map[string]interface{}
        case []interface{}:
                fmt.Println("table is a slice of interface{}")
                for _, tb := range value {
                        if m, ok := tb.(map[string]interface{}); ok {
                                // Now it's accessible
                                fmt.Println(m["name"])

                        }
                }
        default:
                fmt.Println("unknown type")
        }
}

You might want to handle errors better than this.

To read more, check out my writing from a while ago https://medium.com/code-zen/dynamically-creating-instances-from-key-value-pair-map-and-json-in-go-feef83ab9db2.

edited Jan 22, 2018 at 22:58

answered Jan 22, 2018 at 19:42

Pandemonium

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1 Comment

Sanjay Shitole Over a year ago

thanks I tried this ---> r.Name := m["tables"]["name"] but when I compile it gives error invalid operation: m["tables"]["name"] (type interface {} does not support indexing)

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