Accessing fields in nested structs

Question

How do I reference a field in the "AllData" struct below from the main "Forecast" struct? e.g if I wanted to reference "TemperatureMax from Forecast -> Daily?

type AllData struct {
    Time                       float64 `json:"time"`
    Summary                    string  `json:"summary"`
    Icon                       string  `json:"icon"`
    TemperatureMin             float64 `json:"temperatureMin"`
    TemperatureMinTime         float64 `json:"temperatureMinTime"`
    TemperatureMax             float64 `json:"temperatureMax"`
}

type HourlyData struct {
    Summary string        `json:"summary"`
    Icon    string        `json:"icon"`
    Data    []CurrentData `json:"data"`
}

type DailyData struct {
    Summary string    `json:"summary"`
    Icon    string    `json:"icon"`
    Data    []AllData `json:"data"`
}

type Forecast struct {
    Latitude  float64     `json:"latitude"`
    Longitude float64     `json:"longitude"`
    Timezone  string      `json:"timezone"`
    Offset    int         `json:"offset"`
    Currently CurrentData `json:"currently"`
    Hourly    HourlyData  `json:"hourly"`
    Daily     DailyData   `json:"daily"`
    Flags     Flags       `json:"flags"`
}

DailyData.Data is an array, what exactly are you trying to do? — leeor
– leeor, Commented Sep 22, 2015 at 21:25
hi - this mirrors the way the json feed is structured when you pull from forecast.io ( weather forecast). the goal is to eventually access any of the available variables in a fronted visualization. I can't print out any of the values in AllData at this point e.g when using fmt.Printf — user2022284
– user2022284, Commented Sep 22, 2015 at 21:48
Can you include the JSON sample and how you are trying to use it with these data structures? That will help us provide more specific guidance. — MDrollette
– MDrollette, Commented Sep 22, 2015 at 22:07

Carl Veazey · Accepted Answer · 2015-09-22 22:20:30Z

4

You can access an AllData field from a Forecast struct by providing an index into the Data slice in DailyData. Consider this stripped-down example of your question:

package main

import "fmt"

type AllData struct {
    Summary string
}

type DailyData struct {
    Data []AllData
}

type Forecast struct {
    Daily DailyData
}

func main() {
    a := AllData{"summary"}
    s := []AllData{a}
    d := DailyData{s}
    f := Forecast{d}

    val := f.Daily.Data[0].Summary

    fmt.Println(val)
}

In main, we read the Summary field from the AllData struct at index 0 of the DailyData's Data slice. This prints summary to the console.

Optionally, we could access multiple AllData structs by ranging over the slice in DailyData:

func main() {
    a1 := AllData{"summary1"}
    a2 := AllData{"summary2"}
    a3 := AllData{"hello"}
    s := []AllData{a1, a2, a3}
    d := DailyData{s}
    f := Forecast{d}

    for _, val := range f.Daily.Data {
        fmt.Println(val.Summary)
    }
}

The above prints:

summary1
summary2
hello

edited Sep 22, 2015 at 22:20

answered Sep 22, 2015 at 22:10

Carl Veazey

18.4k8 gold badges69 silver badges82 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

user2022284 Over a year ago

Carl - this is great. the first option is closer to what I am looking to do - i.e access the variables in AllData individually ( vs. spitting it all out in a range like in the second option). However, this implies I have to setup variables like this for EACH item in AllData - and there are quite a few - I abbreviated it here for clarity.

Carl Veazey Over a year ago

I'm sorry then I don't really understand what you're trying to do, could you edit your question to specify what you mean beyond accessing the struct members?

Collectives™ on Stack Overflow

Accessing fields in nested structs

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related