Parse nested JSON into struct?

Question

I want to parse the following JSON output:

{ "total":5689, "result":{ "6581":{ "percent":37.79, "count":2150 }, "6591":{ "percent":35.31, "count":2009 }, "6601":{ "percent":26.89, "count":1530 } } }

I have read that JSON can be parsed into a struct if the format is known:

package main import ( "encoding/json" "fmt" "os" ) type VoteResult struct { Total int `json:"total"` Result struct { Efid1 struct { Percent float64 `json:"percent"` Count int `json:"count"` } Efid2 struct { Percent float64 `json:"percent"` Count int `json:"count"` } Efid3 struct { Percent float64 `json:"percent"` Count int `json:"count"` } } } func main() { b := []byte(`{"total":5689,"result":{"6581":{"percent":37.79,"count":2150} ,"6591":{"percent":35.31,"count":2009},"6601":{"percent":26.89,"count":1530}}}`) var v VoteResult err := json.Unmarshal(b, &v) if err != nil { fmt.Fprintf(os.Stderr, "%v\n", err) os.Exit(1) } fmt.Println(v) }

Go Playground

This is the output, but something is wrong as the nested structs are not filled with data:

{5689 {{0 0} {0 0} {0 0}}}

What am I doing wrong?

user94559 · Accepted Answer · 2016-07-25 23:10:20Z

The result part of the JSON is a dictionary mapping strings to objects. Try this instead (https://play.golang.org/p/BCNHw-OH2I):

type VoteResult struct { Total int `json:"total"` Result map[string]struct { Percent float64 `json:"percent"` Count int `json:"count"` } }

EDIT

As an alternative, if those strings are truly fixed, you could do this:

type VoteResult struct { Total int `json:"total"` Result struct { Efid1 struct { Percent float64 `json:"percent"` Count int `json:"count"` } `json:"6581"` Efid2 struct { Percent float64 `json:"percent"` Count int `json:"count"` } `json:"6591"` Efid3 struct { Percent float64 `json:"percent"` Count int `json:"count"` } `json:"6601"` } }

Here we've just decided that Efid1 has the JSON key 6591, etc. But I suspect a map of strings to structs is a better fit for the data structure you have.

He's just missing a tag. Changing his data type to something dynamic isn't a good solution to that problem.
@evanmcdonnal I'm not sure what makes you think that. The default JSON tag for Result is result already. Adding a tag shouldn't (and doesn't when I just tried it) make a difference.
yeah you're right, that works fine and my code was wrong, didn't read the post closely enough. Result needs to be a dictionary because the objects have keys. He could do something like what I have but it doesn't really make sense imo (the three inner structs would also need tags and I bet their names change from one response to another).
@evanmcdonnal Yeah, I added an alternative that shows that approach, but as you said, it's probably not the right thing.
Thanks. I could not figure out where the tags for the inner structs should go, I put them after struct but that did not work. However, I like the first example much better as this is more compact and will also work when name of inner structs change.

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