Golang mapstructure not working as expected

Question

I am trying to decode a map[string]interface{} to a struct, but the "hours" field is not getting populated. I am using https://github.com/mitchellh/mapstructure for decoding. This is the struct:

BusinessAddRequest struct {
        Name       string `json:"name"`
        Phone      string `json:"phone"`
        Website    string `json:"website,omitempty"`
        Street     string `json:"street"`
        City       string `json:"city"`
        PostalCode string `json:"postalCode"`
        State      string `json:"state"`
        Hours []struct {
            Day                 string `json:"day"`
            OpenTimeSessionOne  string `json:"open_time_session_one,omitempty"`
            CloseTimeSessionOne string `json:"close_time_session_one,omitempty"`
            OpenTimeSessionTwo  string `json:"open_time_session_two,omitempty"`
            CloseTimeSessionTwo string `json:"close_time_session_two,omitempty"`
        } `json:"hours"`
        Cuisine []string `json:"cuisine,omitempty"`
        BusinessID int `json:"businessId,omitempty"`
        AddressID  int `json:"addressId,omitempty"`
        UserID     int `json:"userId,omitempty"`
}

And this is the example data:

{
    "name": "Agave ...",
    "phone": "(408) 000-000",
    "street": "Abcd",
    "city": "San",
    "postalCode": "90000",
    "state": "CA",
    "hours": [
      {
        "day": "monday",
        "open_time_session_one": "10:00",
        "close_time_session_one": "21:00"
      }
    ],
    "cuisine": [
      "Mexican, tacos, drinks"
    ],
    "userId": 1
}

All fields are getting populated except "hours".

Answer 1

It could be that you're decoding multiple times into the same BusinessAddRequest variable. Note this doesn't work well when you have structure elements that are slices or maps (this applies BOTH to the mapstructure package and to encoding/json as well!). Always use an empty new variable. If the repetition happens in a loop, declare the variable that you decode to in the loop body (it will be a new copy every time you run through the loop).

package main

import "encoding/json"
import "fmt"
import "github.com/mitchellh/mapstructure"

/* (your struct declaration not quoting it to save space) */

func main() {
    var i map[string]interface{}

    config := &mapstructure.DecoderConfig{
        TagName: "json",
    }

    plan, _ := ioutil.ReadFile("zzz")
    var data []interface{}
    /*err :=*/ json.Unmarshal(plan, &data)
    for j := 0; j < len(data); j++ {
        i = data[j].(map[string]interface{})
        var x BusinessAddRequest /* declared here, so it is clean on every loop */
        config.Result = &x
        decoder, _ := mapstructure.NewDecoder(config)
        decoder.Decode(i)
        fmt.Printf("%+v\n", x)
    }
}

(note I had to use a DecoderConfig with TagName="json" to be able to use your structure definition, which is tagged with "json:" and not "mapstructure:").

If this doesn't help, please check your own code and try to find a minimal example similar to what I posted here that reproduces your problem and add it to the question.