JSON key can either be a string or an object

Question

I want to parse some JSON but one key is either a string or an object.

Here is my current struct: https://github.com/PhillippOhlandt/pmtoapib/blob/master/CollectionItemRequest.go#L10

type CollectionItemRequest struct { Url string `json:"url"` Method string `json:"method"` Header []RequestHeader `json:"header"` Body RequestBody `json:"body"` Description string `json:"description"` }

Here the "Url" attribute can not only a string but also an object.

I started to create an own struct for it that covers the object case.

type CollectionItemRequestUrl struct { Raw string `json:"raw"` } type CollectionItemRequest struct { Url CollectionItemRequestUrl `json:"url"` Method string `json:"method"` Header []RequestHeader `json:"header"` Body RequestBody `json:"body"` Description string `json:"description"` }

But then the string version won't work anymore. Is there a way to have both cases working and getting the value via a getter, like request.Url.Get?

EDIT:

Here are the two versions of the JSON:

 "request": { "url": { "raw": "http://localhost:8081/users?per_page=5&page=2", "protocol": "http", "host": [ "localhost" ], "port": "8081", "path": [ "users" ], "query": [ { "key": "per_page", "value": "5", "equals": true, "description": "" }, { "key": "page", "value": "2", "equals": true, "description": "" } ], "variable": [] },

And

"request": { "url": "http://localhost:8081/users/2",

Note: Only subsets, the whole JSON would be too long.

Possible duplicates: stackoverflow.com/questions/18526046/…, stackoverflow.com/questions/44057958/…, stackoverflow.com/questions/47057240/…, stackoverflow.com/questions/40988252/…, stackoverflow.com/questions/11066946/… — Mr_Pink
– Mr_Pink, Commented Jan 17, 2018 at 16:24
The "duplicates" handle much simpler cases where there are different object types or integer/string, etc. But not string/object in a big nested structure. — Phillipp
– Phillipp, Commented Jan 17, 2018 at 16:26
@Phillipp Some of the answers in the questions @JimB linked should work for you. Specifically, a struct with the UnmarshalJSON function should work just fine in this case. — Tulir
– Tulir, Commented Jan 17, 2018 at 16:32

Iain Duncan · Accepted Answer · 2018-01-17 16:51:33Z

Have a type that has a custom unmarshal method that will first unmarshal into an empty interface and then does a type switch on whether it got a string or a map[string]interface{} such as this:

type example struct { URL myURL `json:"url"` } type myURL struct { url string } func (u *myURL) MarshalJSON() ([]byte, error) { return json.Marshal(u.url) } func (u *myURL) UnmarshalJSON(data []byte) error { var raw interface{} json.Unmarshal(data, &raw) switch raw := raw.(type) { case string: *u = myURL{raw} case map[string]interface{}: *u = myURL{raw["raw"].(string)} } return nil } const myStringURL string = `{"url": "http://www.example.com/as-string"}` const myNestedURL string = `{"url": {"raw": "http://www.example.com/as-nested"}}` func main() { var stringOutput example json.Unmarshal([]byte(myStringURL), &stringOutput) fmt.Println(stringOutput) var nestedOutput example json.Unmarshal([]byte(myNestedURL), &nestedOutput) fmt.Println(nestedOutput) }

Runnable in go playground here:

https://play.golang.org/p/I6KC4aXHpxm

Thanks, that works! I was already on the right path with the UnmarshalJSON method but had some problems assigning the value.

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