arrays - 使用 struct 在 Go 中处理空 JSON 数组

Question

在 golang 中追加结构后，我们有结构并得到空值。在下面的结构中找到我在 golang 中的部分代码。

type XmloutRoomRate struct {    
CancellationPolicy Policies `bson:"cancellationPolicy" json:"cancellationPolicy"`
}


type Policies struct {
    Policies []RoomPolicies `bson:"policies" json:"policies"`
}


type RoomPolicies struct {
    Amount            float64 `bson:"amount" json:"amount"`
    DaysBeforeCheckIn int     `bson:"daysBeforeCheckIn" json:"daysBeforeCheckIn"`
} 

cancelPolicyMain := Policies{}
cancelPolicy := RoomPolicies{}

if cancelAmount < 0 {
  cancelPolicy.Amount = cancelAmount
  cancelPolicy.DaysBeforeCheckIn = cancelDay
  cancelPolicyMain.Policies = append(cancelPolicyMain.Policies, cancelPolicy)
}else{
  cancelPolicyMain = agodaPolicies{}
  cancelPolicyMain.Policies = append(cancelPolicyMain.Policies)
}

当数据出现时获得正确的数据结构。

"cancellationPolicy": {
   "policies": [
                {
                  "amount": 5141.58,
                  "daysBeforeCheckIn": 5
                }
              ]
}

但是当数据不可用时获取空值结构。

"cancellationPolicy": {
            "policies": null
           }

我们需要带有空白数组 [] 的实际输出。

"cancellationPolicy": {
            "policies": []
           }

Answer 1

nil slice 值被编码为 JSON null 值。这记录在 json.Marshal() :

Array and slice values encode as JSON arrays, except that []byte encodes as a base64-encoded string, and a nil slice encodes as the null JSON value.

非 nil 空 slice 被编码为空 JSON 数组。所以只需将 Policies.Policies 初始化为一个非 nil 的空 slice ，它就会在输出中为 []:

cancelPolicyMain = Policies{Policies: []RoomPolicies{}}

测试代码:

const cancelDay = 1

for cancelAmount := -500.0; cancelAmount <= 501; cancelAmount += 1000 {
    cancelPolicyMain := Policies{}
    cancelPolicy := RoomPolicies{}

    if cancelAmount < 0 {
        cancelPolicy.Amount = cancelAmount
        cancelPolicy.DaysBeforeCheckIn = cancelDay
        cancelPolicyMain.Policies = append(cancelPolicyMain.Policies, cancelPolicy)
    } else {
        cancelPolicyMain = Policies{Policies: []RoomPolicies{}}
        cancelPolicyMain.Policies = append(cancelPolicyMain.Policies)
    }

    x := XmloutRoomRate{cancelPolicyMain}
    if err := json.NewEncoder(os.Stdout).Encode(x); err != nil {
        panic(err)
    }
}

输出(在 Go Playground 上尝试):

{"cancellationPolicy":{"policies":[{"amount":-500,"daysBeforeCheckIn":1}]}}
{"cancellationPolicy":{"policies":[]}}