如何解组不一致的JSON字段，该字段可以是字符串*或*字符串数组? [英] How to Unmarshal an inconsistent JSON field that can be a string *or* an array of string?

问题描述

我在解组一些我无法控制的Json时遇到了麻烦. 在一个字段中，有99％的时间是字符串，但偶尔是数组.

I am having trouble Unmarshalling some Json I don't have control over. There is one field that 99% of the time is a string but occasionally is an array.

type MyListItem struct {
    Date  string `json:"date"`
    DisplayName       string `json:"display_name"`
}

type MyListings struct {
    CLItems []MyListItem `json:"myitems"`
}

var mylist MyListings
err = json.Unmarshal(jsn, &mylist)
if err != nil {
    fmt.Print("JSON:\n%s\n error:%v\n", string(jsn),err)
    return
}

Json如下:

{       
    "date": "30 Apr",
    "display_name": "Mr Smith"
},
{
    "date": "30 Apr",
    "display_name": ["Mr Smith", "Mr Jones"],
}

错误:json:无法将数组解组到字符串类型的Go结构字段MyListItem.display_name

error: json: cannot unmarshal array into Go struct field MyListItem.display_name of type string

推荐答案

使用 json.RawMessage 捕获变化的字段.

Use json.RawMessage to capture the varying field.

使用json-"名称对解码器隐藏DisplayName字段.顶级JSON解码后，应用程序将填充此字段.

Use the json "-" name to hide the DisplayName field from decoder. The application will fill this field after the top-level JSON is decoded.

type MyListItem struct {
    Date           string          `json:"date"`
    RawDisplayName json.RawMessage `json:"display_name"`
    DisplayName    []string        `json:"-"`
}

解组顶级JSON:

var li MyListItem
if err := json.Unmarshal(data, &li); err != nil {
    // handle error
}

根据原始数据的类型取消对显示名称的编组:

Unmarshal the display name depending on the type of the raw data:

if len(li.RawDisplayName) > 0 {
    switch li.RawDisplayName[0] {
    case '"':
        if err := json.Unmarshal(li.RawDisplayName, &li.DisplayName); err != nil {
            // handle error
        }
    case '[':
        var s []string
        if err := json.Unmarshal(li.RawDisplayName, &s); err != nil {
            // handle error
        }
        // Join arrays with "&" per OP's comment on the question.
        li.DisplayName = strings.Join(s, "&")
    }
}

游乐场示例

将以上内容合并到for循环中以处理MyListings:

Incorporate the above into a for loop to handle MyListings:

var listings MyListings
if err := json.Unmarshal([]byte(data), &listings); err != nil {
    // handle error
}
for i := range listings.CLItems {
    li := &listings.CLItems[i]
    if len(li.RawDisplayName) > 0 {
        switch li.RawDisplayName[0] {
        case '"':
            if err := json.Unmarshal(li.RawDisplayName, &li.DisplayName); err != nil {
                // handle error
            }
        case '[':
            var s []string
            if err := json.Unmarshal(li.RawDisplayName, &s); err != nil {
                // handle error
            }
            li.DisplayName = strings.Join(s, "&")
        }
    }
}

游乐场示例

如果数据模型中有多个位置，值可以是字符串或[]字符串，则将逻辑封装为类型可能会有所帮助.在 json.Unmarshaler 接口的实现中解析JSON数据.

If there's more than one place in the data model where a value can be a string or []string, it can be helpful to encapsulate the logic in a type. Parse the JSON data in an implementation of the json.Unmarshaler interface.

type multiString string

func (ms *multiString) UnmarshalJSON(data []byte) error {
    if len(data) > 0 {
        switch data[0] {
        case '"':
            var s string
            if err := json.Unmarshal(data, &s); err != nil {
                return err
            }
            *ms = multiString(s)
        case '[':
            var s []string
            if err := json.Unmarshal(data, &s); err != nil {
                return err
            }
            *ms = multiString(strings.Join(s, "&"))
        }
    }
    return nil
}

像这样使用它:

type MyListItem struct {
    Date        string      `json:"date"`
    DisplayName multiString `json:"display_name"`
}

type MyListings struct {
    CLItems []MyListItem `json:"myitems"`
}

var listings MyListings
if err := json.Unmarshal([]byte(data), &listings); err != nil {
    log.Fatal(err)
}

游乐场示例

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