在GO语言中解析嵌套的JSON对象

huangapple
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英文:

Unmarshalling nested JSON objects in GO

问题

我将一些所有对象共有的属性合并到了一个结构体中。

  1. type Document struct {
  2. 	ID        string    `json:"_id,omitempty"`
  3. 	UpdatedAt time.Time `json:"updatedat"`
  4. 	CreatedAt time.Time `json:"createdat"`
  5. }

我还有一个地址结构体，它不是一个文档。

  1. type Address struct {
  2. 	AddressLine string `json:"addressline,omitempty"`
  3. 	City        string `json:"city,omitempty"`
  4. 	Country     string `json:"country,omitempty"`
  5. 	CityCode    int    `json:"citycode,omitempty"`
  6. }

我的客户结构体是一个文档。它还有一个地址属性。

  1. type Customer struct {
  2. 	Document `json:"document"`
  3. 	Address  Address `json:"address"`
  4. 	Name     string  `json:"name,omitempty"`
  5. 	Email    string  `json:"email,omitempty"`
  6. 	Valid    bool    `json:"valid,omitempty"`
  7. }

来自MongoDB的JSON对象如下所示：

  1. [
  2.     {
  3.         "_id": "6186b4556971a9dbae117333",
  4.         "address": {
  5.             "addressline": "Foo Address",
  6.             "city": "Foo City",
  7.             "citycode": 0,
  8.             "country": "Foo Country"
  9.         },
  10.         "document": {
  11.             "createdat": "0001-01-01T03:00:00+03:00",
  12.             "updatedat": "0001-01-01T03:00:00+03:00"
  13.         },
  14.         "email": "foo@mail.com",
  15.         "name": "Foo Fooster",
  16.         "valid": false
  17.     }
  18. ]

我正在使用以下代码进行解组：

  1. var customerEntity Entities.Customer
  2. json.Unmarshal(customerEntityBytes, &customerEntity)

但是我只能得到以下一行。大多数字段都是空的。

  1. {{ 0001-01-01 00:00:00 +0000 UTC 0001-01-01 00:00:00 +0000 UTC} {   0}   false}

我认为这是由于混合的嵌套结构导致的，所以我为测试目的创建了另一个客户结构体；

  1. import "time"
  3. type AutoGenerated []struct {
  4. 	ID      string `json:"_id"`
  5. 	Address struct {
  6. 		Addressline string `json:"addressline"`
  7. 		City        string `json:"city"`
  8. 		Citycode    int    `json:"citycode"`
  9. 		Country     string `json:"country"`
  10. 	} `json:"address"`
  11. 	Document struct {
  12. 		Createdat time.Time `json:"createdat"`
  13. 		Updatedat time.Time `json:"updatedat"`
  14. 	} `json:"document"`
  15. 	Email string `json:"email"`
  16. 	Name  string `json:"name"`
  17. 	Valid bool   `json:"valid"`
  18. }

突然间整个问题都解决了，我能够访问到所有字段。

总结一下，我无法解组我想要使用的Customer结构体。我需要重写unmarshal方法吗？我也查看了一些重写的示例，但代码非常主观。我在基类中进行的更改将导致我改变unmarshal方法。有什么干净的方法可以解决这个问题吗？

英文:

I combined some properties common to all objects into a struct.

  1. type Document struct {
  2. 	ID        string    `json:"_id,omitempty"`
  3. 	UpdatedAt time.Time `json:"updatedat"`
  4. 	CreatedAt time.Time `json:"createdat"`
  5. }

I also have an address struct, which is not a document.

  1. type Address struct {
  2. 	AddressLine string `json:"addressline,omitempty"`
  3. 	City        string `json:"city,omitempty"`
  4. 	Country     string `json:"country,omitempty"`
  5. 	CityCode    int    `json:"citycode,omitempty"`
  6. }

My customer struct is a document. It also has an address property.

  1. type Customer struct {
  2. 	Document `json:"document"`
  3. 	Address  Address `json:"address"`
  4. 	Name     string  `json:"name,omitempty"`
  5. 	Email    string  `json:"email,omitempty"`
  6. 	Valid    bool    `json:"valid,omitempty"`
  7. }

The JSON object from MongoDB is as follows;

  1. [
  2.     {
  3.         "_id": "6186b4556971a9dbae117333",
  4.         "address": {
  5.             "addressline": "Foo Address",
  6.             "city": "Foo City",
  7.             "citycode": 0,
  8.             "country": "Foo Country"
  9.         },
  10.         "document": {
  11.             "createdat": "0001-01-01T03:00:00+03:00",
  12.             "updatedat": "0001-01-01T03:00:00+03:00"
  13.         },
  14.         "email": "foo@mail.com",
  15.         "name": "Foo Fooster",
  16.         "valid": false
  17.     }
  18. ]

I am using the following code to unmarshal this.

  1. 	var customerEntity Entities.Customer
  2. 	json.Unmarshal(customerEntityBytes, &customerEntity)

But all I can get is the following line. Most fields are empty.

  1. {{ 0001-01-01 00:00:00 +0000 UTC 0001-01-01 00:00:00 +0000 UTC} {   0}   false}

As I thought this was due to the mixed nested structure, I created another customer struct for testing purposes;

  1. import "time"
  3. type AutoGenerated []struct {
  4. 	ID      string `json:"_id"`
  5. 	Address struct {
  6. 		Addressline string `json:"addressline"`
  7. 		City        string `json:"city"`
  8. 		Citycode    int    `json:"citycode"`
  9. 		Country     string `json:"country"`
  10. 	} `json:"address"`
  11. 	Document struct {
  12. 		Createdat time.Time `json:"createdat"`
  13. 		Updatedat time.Time `json:"updatedat"`
  14. 	} `json:"document"`
  15. 	Email string `json:"email"`
  16. 	Name  string `json:"name"`
  17. 	Valid bool   `json:"valid"`
  18. }

All of a sudden the whole problem was fixed and I was able to access it with all fields filled.

In summary, I cannot unmarshal the Custumer struct I want to use. Do I need to override the unmarshall method for this? I've also reviewed the override examples but the codes are very subjective. A change I will make in base classes will cause me to change the unmarshall method. What is the clean way to this?

答案1

得分: 3

始终检查错误。

  1. err = json.Unmarshal(customerEntityBytes, &customerEntity)
  2. if err != nil {
  3.     // json: 无法将数组解组为类型为Entities.Customer的Go值
  4. }

原因是，正如@mkopriva指出的那样-你的JSON是一个数组-而你正在解组为单个结构体。要修复：

  1. var customerEntity []Entities.Customer // 使用切片来捕获JSON数组
  2. err = json.Unmarshal(customerEntityBytes, &customerEntity)
  3. if err != nil { /* ... */ }

你当然可以使用自定义类型，但是通过将其嵌套在你的Document结构体中，你会丢失_id标签。要修复，将其提升到Customer中：

  1. type Document struct {
  2.     //ID        string    `json:"_id,omitempty"`
  3.     UpdatedAt time.Time `json:"updatedat"`
  4.     CreatedAt time.Time `json:"createdat"`
  5. }
  7. type Customer struct {
  8.     ID       string `json:"_id,omitempty"`
  9.     
  10.     // ...
  11. }

工作示例：https://play.golang.org/p/EMcC0d1xOLf

英文:

Always check errors.

  1. err = json.Unmarshal(customerEntityBytes, &customerEntity)
  2. if err != nil {
  3.     // json: cannot unmarshal array into Go value of type Entities.Customer
  4. }

and the reason is, as @mkopriva pointed out - your JSON is an array - and you are unmarshaling to a single struct. To fix:

  1.  var customerEntity []Entities.Customer // use slice to capture JSON array
  2.  err = json.Unmarshal(customerEntityBytes, &customerEntity)
  3.  if err != nil { /* ... */ }

You can certainly use your custom types, but you are losing the _id tag by nesting it in your Document struct. To fix, promote it to Customer:

  1. type Document struct {
  2. 	//ID        string    `json:"_id,omitempty"`
  3. 	UpdatedAt time.Time `json:"updatedat"`
  4. 	CreatedAt time.Time `json:"createdat"`
  5. }
  7. type Customer struct {
  8. 	ID       string `json:"_id,omitempty"`
  9. 	
  10.     // ...
  11. }

Working example: https://play.golang.org/p/EMcC0d1xOLf

huangapple
  • 本文由 发表于 2021年11月7日 02:38:51
  • 转载请务必保留本文链接：https://go.coder-hub.com/69866851.html
  • go
  • unmarshalling
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