unmarshal json array into go struct (array is in the middle of the JSON string

Question

I am new to Go. I am working with a weather API. I have commented out the sections that cause the error. I have seen several other links that have a similar problem, however none of them seem to have the array in the middle of the JSON string. I'm sure there is a way to define the struct with a slice. I can't seem to get get the syntax to allow it. Here is where I'm stuck:

package main

import (
    "encoding/json"
    "fmt"
    "io/ioutil"
    "log"
    "net/http"
)

// WeatherData struct to collect data from the API call
type WeatherData struct {
    Wind Wind
    Sys  Sys
    // Weather Weather
    Name string `json:"name"`
}

////////////// ERROR when unmarshalling this struct /////////
// Weather provides basic weather info
// type Weather struct {
//  ID      int    `json:"id"`
//  Descrip string `json:"description"`
//  Icon    string `json:"icon"`
// }
/////////////////////////////////////////////////////////////

// Sys includes sunrise, sunset, country, etc.
type Sys struct {
    Country string `json:"country"`
}

// Wind struct to get specific wind characteristics
type Wind struct {
    Speed  float64 `json:"speed"`
    Degree float64 `json:"deg"`
    Gust   float64 `json:"gust"`
}

func main() {
    res, getErr := http.Get("http://api.openweathermap.org/data/2.5/weather?zip=REMOVED,us&appid=REMOVEDBUTWILLPOSTJSONData")
    if getErr != nil {
        log.Fatalln("http.Get error: ", getErr)
    }
    defer res.Body.Close()
    body, readErr := ioutil.ReadAll(res.Body)
    if readErr != nil {
        log.Fatalln("Read Error: ", readErr)
    }
//////////// UNABLE TO UNMARSHAL the array that passes through here ////
    var data WeatherData
    if err := json.Unmarshal(body, &data); err != nil {
        panic(err)
    }

    fmt.Println("Wind gusts: ", data.Wind.Gust)
    fmt.Println("Wind speed: ", data.Wind.Speed)
    fmt.Println("Wind degrees: ", data.Wind.Degree)

    fmt.Println("Country is: ", data.Sys.Country)
    fmt.Println("City is: ", data.Name)

///////////////// CAN'T ACCESS Description...or anything in Weather
// fmt.Println("Country is: ", data.Weather.Descrip) // cannot access due to this portion being inside an array

}



/////////////////THIS IS THE JSON DATA THAT IS AVAILABLE ///////////
{
  "coord": {
    "lon": -97.31,
    "lat": 32.94
  },
  "weather": [  // CAN'T ACCESS THIS CORRECTLY
    {
      "id": 800,
      "main": "Clear",
      "description": "clear sky",
      "icon": "01d"
    }
  ],
  "base": "stations",
  "main": {
    "temp": 306.46,
    "pressure": 1014,
    "humidity": 55,
    "temp_min": 306.15,
    "temp_max": 307.15
  },
  "visibility": 16093,
  "wind": {
    "speed": 5.1,
    "deg": 150,
    "gust": 7.2
  },
  "clouds": {
    "all": 1
  },
  "dt": 1499120100,
  "sys": {
    "type": 1,
    "id": 2597,
    "message": 0.0225,
    "country": "US",
    "sunrise": 1499081152,
    "sunset": 1499132486
  },
  "id": 0,
  "name": "Fort Worth",
  "cod": 200
}

Additional Links I have viewed with a very similar problem, but solutions don't quite fit my scenario: stackoverflow.com/questions/40626125/… — Logan Wood
– Logan Wood, Commented Jul 4, 2017 at 0:59
This link appears the closest, but I don't know how to create a custom unmarshaller as per their solution description... stackoverflow.com/questions/42377989/… — Logan Wood
– Logan Wood, Commented Jul 4, 2017 at 1:00
UPDATE: It still isn't working, but I have changed: type WeatherData struct { Wind Wind Sys Sys Weather []Weather ////////// this results in the values showing up, but I seem to lose the ability to identify the values based on their keys Name string json:"name"` }` — Logan Wood
– Logan Wood, Commented Jul 4, 2017 at 1:11

jeevatkm · Accepted Answer · 2017-07-04 01:21:22Z

6

You have to define slice of Weather struct in WeatherData.

Uncomment Weather struct and update WeatherData struct to following.

// WeatherData struct to collect data from the API call
type WeatherData struct {
    Wind    Wind      `json:"wind"`
    Sys     Sys       `json:"sys"`
    Weather []Weather `json:"weather"`
    Name    string    `json:"name"`
}

Please have a look on example code: https://play.golang.org/p/4KFqRuxcx2

answered Jul 4, 2017 at 1:21

jeevatkm

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3 Comments

Logan Wood Over a year ago

Thank you for trying to help, but I have been able to do that and get the chunk of array data, however I still can't call an individual key/value for something like data.Weather.Descrip it returns error that it is undefined. I've also tried adding the type []map[string]interface{} which works to give me all key/value pairs, but I still can't call them. You can see my change here: link

jeevatkm Over a year ago

You need to access slice/array values via index, see here: link.

Logan Wood Over a year ago

It works! Thank you so much. I had even gotten as far as accessing the whole thing by index 0, but didn't realize I could do dot notation on top of that. Thanks again!

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