Adding outer tag to resulting JSON when marshalling a slice of structs

Question

I struggle with adding an outer tag to my marshaled JSON struct. Here is my example:

package main

import (
    "encoding/json"
    "fmt"
    "log"
    "time"
)

type tObj struct {
    ModTime time.Time `json:"mTime"`
    Name    string    `json:"mName"`
}

func main() {
    var objs []tObj
    objs = append(objs, getItem("first"))
    objs = append(objs, getItem("second"))

    json, err := json.MarshalIndent(objs, "", "    ")
    if err != nil {
        log.Fatal(err)
    }
    fmt.Println(string(json))
}

func getItem(name string) tObj {
    var t tObj
    t.ModTime = time.Now()
    t.Name = name
    return t
}

So far so good, this gives me something like this:

[{
        "mTime": "2020-06-26T21:29:52.148663+02:00",
        "mName": "first"
    },
    {
        "mTime": "2020-06-26T21:29:52.148666+02:00",
        "mName": "second"
    }
]

All i want is to add an outer tag to the resulting JSON, like this:

{
    "objects": [{
            "mTime": "2020-06-26T21:29:52.148663+02:00",
            "mName": "first"
        },
        {
            "mTime": "2020-06-26T21:29:52.148666+02:00",
            "mName": "second"
        }
    ]
}

I tried to add a json annotation directly to the struct type, but that did not work. What is the easiest way to accomplish this?

Answer 1

You are no longer marshaling an array, you are marshaling an object. You can achieve this by:

json, err := json.MarshalIndent(map[string]interface{}{"objects":objs}, "", "    ")

Answer 2

I struggle with adding an outer tag to my marshaled JSON struct. Here is my example:

package main

import (
    "encoding/json"
    "fmt"
    "log"
    "time"
)

type tObj struct {
    ModTime time.Time `json:"mTime"`
    Name    string    `json:"mName"`
}

func main() {
    var objs []tObj
    objs = append(objs, getItem("first"))
    objs = append(objs, getItem("second"))

    json, err := json.MarshalIndent(objs, "", "    ")
    if err != nil {
        log.Fatal(err)
    }
    fmt.Println(string(json))
}

func getItem(name string) tObj {
    var t tObj
    t.ModTime = time.Now()
    t.Name = name
    return t
}

So far so good, this gives me something like this:

[{
        "mTime": "2020-06-26T21:29:52.148663+02:00",
        "mName": "first"
    },
    {
        "mTime": "2020-06-26T21:29:52.148666+02:00",
        "mName": "second"
    }
]

All i want is to add an outer tag to the resulting JSON, like this:

{
    "objects": [{
            "mTime": "2020-06-26T21:29:52.148663+02:00",
            "mName": "first"
        },
        {
            "mTime": "2020-06-26T21:29:52.148666+02:00",
            "mName": "second"
        }
    ]
}

I tried to add a json annotation directly to the struct type, but that did not work. What is the easiest way to accomplish this?