是否有可能在杜松子酒绑定的 json 中消失 scope？

Question

I'm writing an api server with gin-gonic.

And I got in trouble that associated with marshaling json.

For example, I have a Structure likes below.

type Foo struct {
    Value     float32 `json:"value"`
    Injection interface{}
}

And I wrote down some fields in run time and send response.

r.GET("/ping", func(c *gin.Context) {

    var foo = &Foo{
        Value: 19.8,
        Injection: map[string]interface{}{
            "unit": "C",
            "constraints": map[string]interface{}{
                "min": 18,
                "max": 30,
            },
        },
    }

    c.JSON(200, foo)
})

As a result, I can see this json response.

{
    "value": 19.8,
    "Injection": {
        "constraints": {
            "max": 30,
            "min": 18
        },
        "unit": "C"
    }
}

But if I want to have likes below, what can I do?

{
    "value": 19.8,
    "constraints": {
        "max": 30,
        "min": 18
    },
    "unit": "C"
}

I tried to assign all field in run time, It's work properly in first time, but after add many many fields I met hell gate.

So I can say It's similar problem <Fragment> tag in React.

ps. sorry I can't sure the title is correspond with my mean.

Answer 1

You can use the map directly instead of Foo .

r.GET("/ping", func(c *gin.Context) {
    var data = map[string]interface{}{
        "value": 19.8,
        "unit":  "C",
        "constraints": map[string]interface{}{
            "min": 18,
            "max": 30,
        },
    }

    c.JSON(200, data)
})

If you need something more generic you could have Foo implement the json.Marshaler interface and have the implementation marshal the two values separately and then just "merge" the results manually.

type Foo struct {
    Value     float32     `json:"value"`
    Injection interface{} `json:"-"`
}

func (f *Foo) MarshalJSON() ([]byte, error) {
    type tmp Foo
    out1, err := json.Marshal((*tmp)(f))
    if err != nil {
        return nil, err
    }
    out2, err := json.Marshal(f.Injection)
    if err != nil {
        return nil, err
    }

    out1[len(out1)-1] = ','           // replace the '}' at the end with ','
    out2 = out2[1:]                   // drop the leading '{'
    return append(out1, out2...), nil // merge
}

Note the above assumes that Injection holds a value that will be marshaled into a json object , if the value is a scalar, or a slice type, you'll need to handle those cases differently.

https://play.golang.com/p/kYIu6HnqVIp