CODEWITHSUNDEEP
go
Ratatouille
Ratatouille

Reputation: 1492

create array of struct from by decoding a JSON file in go

All I looking to do is to create an array of struct Response from a json encoded file.

the file that contains json data looks like this.

cat init.txt

{"events": [{"action":"cpr","id":69,"sha1":"abc","cpr":"cpr_data0"},{"action":"cpr","id":85,"sha1":"def","cpr":"cpr_data1"}]}

The way I have gone about approaching this is

But somehow when I inspect the Value they all look 0 or empty

map[events:[{ 0 } { 0 }]

What is wrong with the approach mentioned above.

type Response struct {
  action string `json:"action"`
  id     int64  `json:"id"`
  sha1   string `json:"sha1"`
  cpr    string `json:"cpr"`
}

func main() {
  file, err := os.Open("init.txt")
  if err != nil {
    fmt.Println(err)
    os.Exit(1)
  }
  var response map[string][]Response
  err = json.NewDecoder(file).Decode(&response)
  if err != nil {
    fmt.Println(err)
    os.Exit(1)
  }

  var responseArray []Response
  responseArray = response["events"]
  for _, responseStruct := range responseArray {
    fmt.Println("id =", responseStruct.id)
    fmt.Println("action =", responseStruct.action)
    fmt.Println("sha1 = ", responseStruct.sha1)
    fmt.Println("cpr =", responseStruct.cpr)
    fmt.Println("==========")
  }
  fmt.Println(response)
}

Well If I modify the struct to look like this it works

type Response struct {
  Action string `json:"action"`
  ID     int64  `json:"id"`
  Sha1   string `json:"sha1"`
  Cpr    string `json:"cpr"`
}

So my question is this how the stuff would work, can't I get the above code to work in the way it is?

Upvotes: 0

Views: 1891

Answers (2)

David Maze
David Maze

Reputation: 159875

Go has the notion of public and private fields in objects, and the only distinction is whether they start with an initial capital letter or not. This applies to not just code modules but also the reflect package and things that use it. So in your initial version

type Response struct {
  action string `json:"action"`
  ...
}

nothing outside your source package, not even the "encoding/json" module, can see the private fields, so it can't fill them in. Changing these to public fields by capitalizing Action and the other field names makes them visible to the JSON decoder.

Upvotes: 2

avertocle
avertocle

Reputation: 621

Lowercase struct elements in golang are private, Hence json decoder (which is an external package) can't access them. Its able to create the struct object but not able to set values. They appear zero because they 0 is default value.

Upvotes: 0

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