如何在Golang中创建词典列表？

Question

I'm newbie with Golang.

I want to create a list of dictionaries with resizable capability (this is not static) with append some dict to the list, finally write it on a file, but I confused.

I want something like that:

[
 {"port": 161, "timeout": 1, "sleep_time": 5, "metrics": [
  {"tag_name": "output_current", "id": 3},
  {"tag_name": "input_voltage", "id": 2}
 ]},
 {"port": 161, "timeout": 1, "sleep_time": 4, "metrics": [
   {"tag_name": "destructor", "id": 10}
 ]}
]

---

[UPDATE]:

What is the .append() Python equivalent in Go language something like that?

list_ = []
dict_ = {"key": val}
list_.append(dict_)

I found the answer to this section ([UPDATE]) by borrowing this answer:

type Dictionary map[string]interface{}
data := []Dictionary{}
dict1 := Dictionary{"key": 1}
dict2 := Dictionary{"key": 2}
data = append(data, dict1, dict2)

Answer 1

If you need the data to be stored in a dictionary, using a combination of slice and map[string]interface{} is enough.

In this example below, I created a new type called Dictionary, to avoid writing too many map[string]interface{} syntax on composite literals.

type Dictionary map[string]interface{}

data := []Dictionary{
    {
        "metrics": []Dictionary{
            { "tag_name": "output_current", "id": 3 },
            { "tag_name": "input_voltage", "id": 2 },
        },
        "port":       161,
        "timeout":    1,
        "sleep_time": 5,
    },
    {
        "metrics": []Dictionary{
            { "tag_name": "destructor", "id": 10 },
        },
        "port":       161,
        "timeout":    1,
        "sleep_time": 4,
    },
}

---

But I suggest, if your data structure is fixed, then define a struct instead. Below is an another example using same dataset but in struct object:

type Metric struct {
    TagName string `json:"tag_name"`
    ID      int    `json:"id"`
}

type Data struct {
    Port      int      `json:"port"`
    Timeout   int      `json:"timeout"`
    SleepTime int      `json:"sleep_time"`
    Metrics   []Metric `json:"metrics"`
}

data := []Data{
    Data{
        Port:      161,
        Timeout:   1,
        SleepTime: 5,
        Metrics: []Metric{
            Metric{TagName: "output_current", ID: 3},
            Metric{TagName: "input_voltage", ID: 2},
        },
    },
    Data{
        Port:      161,
        Timeout:   1,
        SleepTime: 4,
        Metrics: []Metric{
            Metric{TagName: "destructor", ID: 10},
        },
    },
}

---

Update 1

To be able to write the data in json file, the data need to be converted into json string first. Use json.Marshal() to do the conversion from map data (or struct object data) to json string, in []byte type.

buf, err := json.Marshal(data)
if err !=nil {
    panic(err)
}

err = ioutil.WriteFile("fileame.json", buf, 0644)
if err !=nil {
    panic(err)
}

Then use ioutil.WriteFile() to write it into file.

---

If you somehow need to print the json string, cast the buf into string type first.

jsonString := string(buf)
fmt.Println(jsonString)

Statements above will generate output below:

[{"port":161,"timeout":1,"sleep_time":5,"metrics":[{"tag_name":"output_current","id":"3"},{"tag_name":"input_voltage","id":"2"}]},{"port":161,"timeout":1,"sleep_time":4,"metrics":[{"tag_name":"destructor","id":"10"}]}]