英文:
How do I inline fields when marshalling JSON?
问题
我有一个名为MonthYear的类型定义，如下所示：
type MonthYear time.Time
func (my *MonthYear) MarshalJSON() ([]byte, error) {
t := time.Time(*my)
return json.Marshal(&struct {
Month int `json:"month"`
Year int `json:"year"`
}{
Month: int(t.Month()) - 1,
Year: t.Year(),
})
}
我在许多不同的结构体中包含它，例如：
type Event struct {
Name string `json:"name"`
Date MonthYear
}
type Item struct {
Category string `json:"category"`
Date MonthYear
}
如何内联MonthYear类型，以便生成的JSON不包含任何嵌入对象？
我希望结果看起来像{ "name": "party", "month": 2, "year": 2017 }和{ "category": "art", "month": 3, "year": 2016 }，而无需为每个结构体编写MarshalJSON方法。
英文:
I have a type MonthYear defined like
type MonthYear time.Time
func (my *MonthYear) MarshalJSON() ([]byte, error) {
t := time.Time(*my)
return json.Marshal(&struct {
Month int `json:"month"`
Year int `json:"year"`
}{
Month: int(t.Month()) - 1,
Year: t.Year(),
})
}
I'm including it a lot of different structs like
type Event struct {
Name string `json:"name"`
Date MonthYear
}
type Item struct {
Category string `json:"category"`
Date MonthYear
}
How do I inline the MonthYear type so that the resulting JSON does not have any embedded objects?
I want the result to look like { "name": "party", "month": 2, "year": 2017 } and { "category": "art", "month": 3, "year": 2016 } without having to write the MarshalJSON for each of the structs.
答案1
得分: 5
我知道这不是你希望得到的答案，但在encoding/json包添加内联支持之前，你可以使用以下解决方法：
将你的MonthYear定义为一个结构体，例如：
type MonthYear struct {
t time.Time
Month int `json:"month"`
Year int `json:"year"`
}
为了方便创建，可以添加一个可选的构造函数：
func NewMonthYear(t time.Time) MonthYear {
return MonthYear{
t: t,
Month: int(t.Month()) - 1,
Year: t.Year(),
}
}
然后使用嵌入（匿名字段）而不是常规（命名）字段，以在JSON表示中实现“扁平化”/内联化：
type Event struct {
Name string `json:"name"`
MonthYear
}
type Item struct {
Category string `json:"category"`
MonthYear
}
作为额外的好处，你可以直接引用字段，例如Event.Year或Event.Month。
进行测试：
evt := Event{Name: "party", MonthYear: NewMonthYear(time.Now())}
fmt.Println(json.NewEncoder(os.Stdout).Encode(evt), evt.Year)
itm := Item{Category: "Tool", MonthYear: NewMonthYear(time.Now())}
fmt.Println(json.NewEncoder(os.Stdout).Encode(itm))
输出结果（在Go Playground上尝试）：
{"name":"party","month":10,"year":2009}
<nil> 2009
{"category":"Tool","month":10,"year":2009}
<nil>
注意：这里的MonthYear.t时间字段没有起作用（也不会被编组）。如果不需要原始的time.Time，可以将其删除。
英文:
I know this is not the answer you wish to receive, but until inline support is added to the encoding/json package, you may use the following workaround:
Make your MonthYear a struct, e.g.:
type MonthYear struct {
t time.Time
Month int `json:"month"`
Year int `json:"year"`
}
An optional, constructor function for easy creation:
func NewMonthYear(t time.Time) MonthYear {
return MonthYear{
t: t,
Month: int(t.Month()) - 1,
Year: t.Year(),
}
}
And use embedding (anonymous field) instead of a regular (named) field to get "flattened" / inlined in the JSON representation:
type Event struct {
Name string `json:"name"`
MonthYear
}
type Item struct {
Category string `json:"category"`
MonthYear
}
As an extra, you'll be able to refer to fields directly like Event.Year or Event.Month which is nice.
Testing it:
evt := Event{Name: "party", MonthYear: NewMonthYear(time.Now())}
fmt.Println(json.NewEncoder(os.Stdout).Encode(evt), evt.Year)
itm := Item{Category: "Tool", MonthYear: NewMonthYear(time.Now())}
fmt.Println(json.NewEncoder(os.Stdout).Encode(itm))
Output (try it on the Go Playground):
{"name":"party","month":10,"year":2009}
<nil> 2009
{"category":"Tool","month":10,"year":2009}
<nil>
Note: The MonthYear.t time field does not play a role here (it is not marshaled either). You can remove it if the original time.Time is not needed.
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