How to Unmarshal Dynamic JSON Keys into Struct Fields in Go?

Unmarshalling Dynamic JSON Keys into Struct Fields in Go

Dynamic JSON keys can pose a challenge when unmarshalling into structs with static field names. Consider the following JSON configuration file:

{
  "things" :{
    "123abc" :{
      "key1": "anything",
      "key2" : "more"
    },
    "456xyz" :{
      "key1": "anything2",
      "key2" : "more2"
    },
    "blah" :{
      "key1": "anything3",
      "key2" : "more3"
    }
  }
}

To represent this JSON in a Go struct, you can use a map instead of static field names:

type X struct {
    Things map[string]Thing
}

type Thing struct {
    Key1 string
    Key2 string
}

Then, unmarshal the JSON using the json.Unmarshal function:

var x X
if err := json.Unmarshal(data, &x); err != nil {
    // handle error
}

With this approach, the dynamic keys become the keys of the map, allowing you to access the values as needed.

However, if the key must be a member of the Thing struct, you can write a loop to add the key after unmarshalling:

type Thing struct {
    Name string `json:"-"` // add the field
    Key1 string
    Key2 string
}

...

// Fix the name field after unmarshal
for k, t := range x.Things {
    t.Name = k
    x.Things[k] = t
}

This method allows you to have both the key as a field and the dynamic values.

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