为什么在Golang中使用Json Unmarshall时会改变数组类型？

huangapple
go评论109阅读模式
英文:

Why Json Unmarshall changing array type in Golang?

问题

我正在尝试以功能方式填充我的Postgres数据库。在我的情况下，SeedSchema()函数可以接受任何类型的结构体。因此，我定义了一个接口，并创建了用于填充结构体的函数。我尝试过使用泛型和不使用泛型。

当我将任何JSON数组作为字节数组从文件中解组时，json.Unmarshal方法会更改我的结构体的tempMember成员。例如，models.Term变为map[string]interface{}。在此函数之前，我已经使用了unmarshal，并没有遇到这种情况。

这是我的SeedSchema()函数：

  1. func (db *Database) SeedSchema(models ...globals.Seeder[any]) error {
  2. 	var (
  3. 		subjects []globals.Seeder[any]
  4. 		fileByte []byte
  5. 		err      error
  6. 		// tempMember any
  7. 	)
  8. 	if len(models) == 0 {
  9. 		subjects = seederModelList
  10. 	} else {
  11. 		subjects = models
  12. 	}
  13. 	for _, model := range subjects {
  14. 		fileName, tempMember := model.Seed()
  15. 		fmt.Printf("%+v\n", reflect.TypeOf(tempMember)) //1
  16. 		if fileByte, err = os.ReadFile("db/seeds/" + fileName); err != nil {
  17. 			fmt.Println(err)
  18. 			return err
  19. 		}
  20. 		if err = json.Unmarshal(fileByte, &tempMember); err != nil {
  21. 			fmt.Println(err)
  22. 			return err
  23. 		}
  24. 		fmt.Printf("%+v\n", reflect.TypeOf(tempMember)) //2
  26. 	}
  27. 	return nil 
  28. }

第一个打印语句返回[]models.AirportCodes，第二个打印语句返回[]interface{}。

这是我的接口和模型：

  1. func (AirportCodes) Seed() (string, any) {
  2. 	return "airport_codes.json", []AirportCodes{}
  3. }
  5. type Seeder[T any] interface {
  6. 	Seed() (string, T)
  7. 	// Seed(*gorm.DB) error
  8. 	TableName() string
  9. }
  11. seederModelList = []globals.Seeder[any]{
  12. 		m.AirportCodes{},
  13. 		m.Term{},
  14. 	}
英文:

I'm trying to seed my Postgres database as functionally. In my case, SeedSchema() function can take any type struct. So I define a interface and create functions to my structs which will seed. I tried with generics and without.

When I unmarshall any json array from file as byte array, json.Unmarshall method change my tempMember member of struct. Exp, models.Term to map[string]interface{}. I've used unmarshall before this function and I've not seen like this situation.

Here is my SeedSchema() function:

  1. func (db *Database) SeedSchema(models ...globals.Seeder[any]) error {
  2. var (
  3. 	subjects []globals.Seeder[any]
  4. 	fileByte []byte
  5. 	err      error
  6. 	// tempMember any
  7. )
  8. if len(models) == 0 {
  9. 	subjects = seederModelList
  10. } else {
  11. 	subjects = models
  12. }
  13. for _, model := range subjects {
  14. 	fileName, tempMember := model.Seed()
  15. 	fmt.Printf("%+v\n", reflect.TypeOf(tempMember)) //1
  16. 	if fileByte, err = os.ReadFile("db/seeds/" + fileName); err != nil {
  17. 		fmt.Println(err)
  18. 		return err
  19. 	}
  20. 	if err = json.Unmarshal(fileByte, &tempMember); err != nil {
  21. 		fmt.Println(err)
  22. 		return err
  23. 	}
  24. 	fmt.Printf("%+v\n", reflect.TypeOf(tempMember)) //2
  26. }
  27. return nil 
  28. }

First print returns []models.AirportCodes and the second []interface {}.

Here is my interface and model:

  1. func (AirportCodes) Seed() (string, any) {
  2. 	return "airport_codes.json", []AirportCodes{}
  3. }
  5. type Seeder[T any] interface {
  6. 	Seed() (string, T)
  7. 	// Seed(*gorm.DB) error
  8. 	TableName() string
  9. }
  11. seederModelList = []globals.Seeder[any]{
  12. 		m.AirportCodes{},
  13. 		m.Term{},
  14. 	}

答案1

得分: 1

几周后，我一直在寻找解决这个问题的方法，并查看了解组接口和示例。然后，就像icza所说的那样，我开始检查我的代码，了解类型之间的约定，并且我像这样解决了问题。如果你们有比我更好的答案，请添加回答。

数据：

  1. [
  2.     {
  3.         "id":1,
  4.         "name":"Term 1",
  5.         "content": [
  6.             "a1",
  7.             "a2",
  8.             "a3"
  9.         ]
  10.     }
  11. ]

结果：

  1. [{ID:1 Name:Term 1 Content:[a1 a2 a3]}]

UnmarshalJSON 函数：

  1. func (term *Term) UnmarshalJSON(data []byte) error {
  2. 	tempMap := map[string]interface{}{}
  3. 	if err := json.Unmarshal(data, &tempMap); err != nil {
  4. 		return err
  5. 	}
  6. 	*term = Term{
  7. 		Name: tempMap["name"].(string),
  8. 	}
  9. 	if tempMap["content"] != nil {
  10. 		for _, v := range tempMap["content"].([]interface{}) {
  11. 			(*term).Content = append((term).Content, v.(string))
  12. 		}
  13. 	}
  14. 	return nil
  15. }

谢谢你的评论。

英文:

After a few weeks, I have looking for solve this problem and look unmarshaler interfaces and examples. Then Like what icza said, I started to look over the my code that convention between types and I solved like this. If you guys have better answer than mine, please add answer.

Data:

  1. [
  2.     {
  3.         "id":1,
  4.         "name":"Term 1",
  5.         "content": [
  6.             "a1",
  7.             "a2",
  8.             "a3"
  9.         ]
  10.     }
  11. ]

Result:

  1. [{ID:1 Name:Term 1 Content:[a1 a2 a3]}]

UnmarshalJSON Function:

  1. func (term *Term) UnmarshalJSON(data []byte) error {
  2. 	tempMap := map[string]interface{}{}
  3. 	if err := json.Unmarshal(data, &tempMap); err != nil {
  4. 		return err
  5. 	}
  6. 	*term = Term{
  7. 		Name: tempMap["name"].(string),
  8. 	}
  9. 	if tempMap["content"] != nil {
  10. 		for _, v := range tempMap["content"].([]interface{}) {
  11. 			(*term).Content = append((term).Content, v.(string))
  12. 		}
  13. 	}
  14. 	return nil
  15. }

Thank you for comments.

huangapple
  • 本文由 发表于 2022年9月2日 16:27:58
  • 转载请务必保留本文链接：https://go.coder-hub.com/73579783.html
  • go
  • unmarshalling
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