JSON to struct conversion

Question

This is the struct I have:

type Resource struct {
    Name string `json:"name"`
    Ranges struct {
        Range []struct {
            Begin int `json:"begin"`
            End   int `json:"end"`
        } `json:"range"`
    } `json:"ranges,omitempty"`
    Role string `json:"role,omitempty"`
    Type string `json:"type"`
    Scalar Scalar `json:"scalar,omitempty"`
}

I don't know how to make fields in the JSON not null. For example, struct Range like that:

{
    "name": "cpus",
    "ranges": {
        "range": null
    },
    "type": "SCALAR",
    "scalar": {
        "value": 1
    }
}, {
    "name": "mem",
    "ranges": {
        "range": null
}

Please create Minimal, Complete, and Verifiable example. Post the json that you want to unmarshal — Himanshu
– Himanshu, Commented Mar 3, 2018 at 18:27
Either allocate the value of the Range field so that it isn't nil, or add ,omitempty to the json tag so that the json property is omitted if the Range field is nil. See here: play.golang.org/p/GWWm5yAP7lU — mkopriva
– mkopriva, Commented Mar 3, 2018 at 18:40
You can also define a type that will implement the json.Marshaler interface and have it decide how it's gonna be marshaled if it's empty or nil. play.golang.org/p/UJK5cjkctIw — mkopriva
– mkopriva, Commented Mar 3, 2018 at 21:06

CallMeLoki · Accepted Answer · 2018-03-03 20:04:37Z

0

a way to do that is assign range as *string and then you should compare it with nil or not, if not nil convert it to string and marshall it again

answered Mar 3, 2018 at 20:04

CallMeLoki

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2 Comments

Emil Over a year ago

This doesn't make sense to me

CallMeLoki Over a year ago

the range field you assign with []struct can be pointer to a string

iFreezy · Accepted Answer · 2018-03-05 13:47:23Z

0

That changes struct is resolved my problem:

type Resource struct {
    Name   string  `json:"name"`
    Ranges *Ranges  `json:"ranges,omitempty"`
    Role   string  `json:"role,omitempty"`
    Type   string  `json:"type"`
    Scalar *Scalar `json:"scalar,omitempty"`
}

answered Mar 5, 2018 at 13:47

iFreezy

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Comments

Zak · Accepted Answer · 2018-03-06 08:40:10Z

assuming that you want to marshal the structs in your question and get a json output that looks like this:

  {
    "name": "cpus",
    "ranges": {
      "range": []
    },
    "type": "SCALAR",
    "scalar": {
      "value": 1
    }
  },
  {
    "name": "mem",
    "ranges": {
      "range": []
    }
  }

In golang slices [] are a reference type, that are backed by an array. You can read up on the internals of slices here: https://blog.golang.org/go-slices-usage-and-internals

Basically the reason that you are getting null in the output is because you have not instantiated the slice, the slice is essentially a pointer, and that pointer is nil.

Create a new empty slice, like []Range{} and assign that to the field in Resource that is currently null in the json, and instead of a nil pointer, you will have an empty slice that will be marshalled as [] and not null.

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