json.Unmarshal returning blank structure

Question

I have a JSON blob that looks like this

{     "metadata":{         "id":"2377f625-619b-4e20-90af-9a6cbfb80040",         "from":"2014-12-30T07:23:42.000Z",         "to":"2015-01-14T05:11:51.000Z",         "entryCount":801,         "size":821472,         "deprecated":false     },     "status":[{          "node_id":"de713614-be3d-4c39-a3f8-1154957e46a6",          "status":"PUBLISHED"     }] } 

and I have a little code to transform that back into go structs

type Status struct {     status string     node_id string }  type Meta struct {     to string     from string     id string     entryCount int64     size int64     depricated bool }  type Mydata struct {     met meta     stat []status }  var realdata Mydata err1 := json.Unmarshal(data, &realdata) if err1 != nil {     fmt.Println("error:", err1) } fmt.Printf("%T: %+v\n", realdata, realdata) 

but what I see when I run this is just a zeroed structure

main.Mydata: {met:{to: from: id: entryCount:0 size:0 depricated:false} stat:[]} 

I tried allocating the struct first but that also didn't work, I'm not sure why its not producing values, and its not returning an error

Answer 1

Your struct fields are not exported. This is because they start with a lowercase letter.

EntryCount // <--- Exported entryCount // <--- Not exported 

When I say "not exported", I mean they are not visible outside of your package. Your package can happily access them because they are scoped locally to it.

As for the encoding/json package though - it cannot see them. You need to make all of your fields visible to the encoding/json package by making them all start with an uppercase letter, thereby exporting them:

type Status struct {     Status  string     Node_id string }  type Meta struct {     To         string     From       string     Id         string     EntryCount int64     Size       int64     Depricated bool }  type Mydata struct {     Metadata  Meta     Status []Status } 

See it working on the Go Playground here

You should also reference the Golang specification for answers. Specifically, the part that talks about Exported Identifiers.