Golang JSON Serialization/Deserialization

Question

I have a struct as follows:

type Node struct {
    Name     string
    Children []*Node
    Values   []string
}

I also have a set of json files describing my trees such as:

{
  "something": {
    "someblah": [
      "fluf",
      "glah"
    ],
    "someother": {
      "someotter": [
        "blib",
        "fnar"
      ]
    }
  }
}

How can I deserialize these files into the structs?

All the examples I found seem to require a different structure with named key/value pairs.

For this, the structure is key:

the key is the struct name
the map contents are children
the lists contents are values

I cannot understand how to map this logic into the golang json serializer.

why not unmarshal into map[string]interface{}?

ifnotak
– ifnotak

2019-03-23 22:45:13 +00:00
Commented Mar 23, 2019 at 22:45 — ifnotak
– ifnotak, Commented Mar 23, 2019 at 22:45

score 4 · Accepted Answer · 2019-03-24 20:38:52Z

4

The easiest approach is to decode to map[string]interface{} and convert that to the desired structure:

var m map[string]interface{}
err := json.Unmarshal(data, &m)
if err != nil {
    // handle error
}
node := convert(m, "")

...

func convert(name string, m map[string]interface{}) *Node {
    n := Node{Name: name}
    for k, v := range m {
        switch v := v.(type) {
        case []interface{}:
            nn := Node{Name: k}
            for _, e := range v {
                s, ok := e.(string)
                if !ok {
                    panic(fmt.Sprintf("expected string, got %T", e))
                }
                nn.Values = append(nn.Values, s)
            }
            n.Children = append(n.Children, &nn)
        case map[string]interface{}:
            n.Children = append(n.Children, convert(k, v))
        default:
            panic("unexpected type")
        }
    }
    return &n
}

The convert function panics when it encounters a value of an unexpected type. Depending on the requirements of your application, you may want to ignore these values or return an error.

Run it on the playground.

edited Mar 24, 2019 at 20:38

answered Mar 23, 2019 at 23:04

user5728991

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2 Comments

Wilbert Over a year ago

Thanks, this helped me find the correct solution. However, there seems to be a bug in the example: In the values case, there is no node created and the values are attached to the parent. In the example, each node has either children or values.

user5728991 Over a year ago

@Wilbert See updated answer. It would have been helpful if the question showed an example of the expected result.

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