Insert arrays into json object in golang

Question

I am processing data from a text file with go and would like to ouput a json record like this:

[{
        "ship": "RMS Titanic",
        "crew": [{
            "name": "Captain Smith"
        }, {
            "name": "First Officer Murdoch"
        }],
        "passengers": [{
            "name": "Jack Dawson"
        }, {
            "name": "Rose Dewitt Bukater"
        }]
    },
    {
        "ship": "ship2",
        "crew": [{
            "name": "crew 1"
        }, {
            "name": "crew 2"
        }],
        "passengers": [{
            "name": "passenger 1"
        }, {
            "name": "passenger 2"
        }]
    }
]

Here is a snippet from my code:

package main

import (
        "fmt"
        "encoding/json"
)

func main() {
        var crew []map[string]string
        var passengers []map[string]string

        s1 := map[string]string{ "name": "RMS Titanic"}
        j1, _ := json.Marshal(s1)
        fmt.Printf("j1: %s\n", string(j1))

        s2 := map[string]string{ "name": "Captain Smith" }
        crew = append(crew, s2)
        s2 = map[string]string{ "name": "First Officer Murdoch" }
        crew = append(crew, s2)
        j2, _ := json.Marshal(crew)
        fmt.Printf("j2: %s\n", string(j2))

        s3 := map[string]string{ "name": "Jack Dawson"}
        passengers = append(passengers, s3)
        s3 = map[string]string{ "name": "Rose Dewitt Bukater" }
        passengers = append(passengers, s3)

        j3, _ := json.Marshal(passengers)
        fmt.Printf("j3: %s\n", string(j3))

        s4 :=  map[string]string{"crew": string(j2), "passengers": string(j3)}
        j4, _ := json.Marshal(s4)
        fmt.Printf("j4: %s\n", string(j4))

}

Output:

j1: {"name":"RMS Titanic"}
j2: [{"name":"Captain Smith"},{"name":"First Officer Murdoch"}]
j3: [{"name":"Jack Dawson"},{"name":"Rose Dewitt Bukater"}]
j4: {"crew":"[{\"name\":\"Captain Smith\"},{\"name\":\"First Officer Murdoch\"}]","passengers":"[{\"name\":\"Jack Dawson\"},{\"name\":\"Rose Dewitt Bukater\"}]"}

I am processing the ship data in j1, the crew data in j2 and the passengers data in j3.

I have managed to merge j2 and j3 together into j4, but the quotation mark s are escapaded, how un-escape the quotation marks ?

How to insert j1 data in there so the output match the json output I wish for ?

This 3rd party lib might be of great help to you: github.com/icza/dyno (disclosure: I'm the author). — icza
– icza, Commented Mar 18, 2018 at 13:32

janos · Accepted Answer · 2018-03-18 06:28:55Z

1

The solution is not to unescape the string, but to marshal the complete structure you want to serialize to JSON, for example:

ship1 := map[string]interface{}{
    "ship": "RMS Titanic",
    "crew": crew,
    "passengers": passengers,
}

ship1Json, err := json.Marshal(ship1)
if err != nil {
    panic(err)
}

fmt.Println("ship1:", string(ship1Json))

Another example with two ships in a slice:

ship2 := map[string]interface{}{
    "ship": "ship2",
    "crew": crew,
    "passengers": passengers,
}

ships := []map[string]interface{}{ship1, ship2}

shipsJson, err := json.Marshal(ships)
if err != nil {
    panic(err)
}

fmt.Println("ships:", string(shipsJson))

The result is easier to see if we print the JSON indented:

indented, err := json.MarshalIndent(ships, "", "  ")
if err != nil {
    panic(err)
}

fmt.Println(string(indented))

Giving:

[
  {
    "crew": [
      {
        "name": "Captain Smith"
      },
      {
        "name": "First Officer Murdoch"
      }
    ],
    "passengers": [
      {
        "name": "Jack Dawson"
      },
      {
        "name": "Rose Dewitt Bukater"
      }
    ],
    "ship": "RMS Titanic"
  },
  {
    "crew": [
      {
        "name": "Captain Smith"
      },
      {
        "name": "First Officer Murdoch"
      }
    ],
    "passengers": [
      {
        "name": "Jack Dawson"
      },
      {
        "name": "Rose Dewitt Bukater"
      }
    ],
    "ship": "ship2"
  }
]

2 Comments

tjoe Over a year ago

Thank you, very good ! Is there a way to insert s1 directly in ship1 ? I tried ship1 := map[string]interface{}{ s1, "crew": crew,"passengers": passengers} but I got and error missing key in map literal.

janos Over a year ago

@tjoe ship1 := map[string]interface{}{ "ship": s1, "crew": crew,"passengers": passengers}

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