Golang dynamically creating member of struct

Question

You will need to use a map (of type map[string]interface{}) to work with dynamic JSON. Here is an example of creating a new map:

// Initial declaration
m := map[string]interface{}{
    "key": "value",
}

// Dynamically add a sub-map
m["sub"] = map[string]interface{}{
    "deepKey": "deepValue",
}

Unmarshalling JSON into a map looks like:

var f interface{}
err := json.Unmarshal(b, &f)

The code above would leave you with a map in f, with a structure resembling:

f = map[string]interface{}{
    "Name": "Wednesday",
    "Age":  6,
    "Parents": []interface{}{
        "Gomez",
        "Morticia",
    },
}

You will need to use a type assertion to access it, otherwise Go won’t know it’s a map:

m := f.(map[string]interface{})

You will also need to use assertions or type switches on each item you pull out of the map. Dealing with unstructured JSON is a hassle.

More information:

https://blog.golang.org/json-and-go
https://godoc.org/encoding/json#Unmarshal

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