在`json.Marshal()`中指定结构格式。

huangapple
go评论110阅读模式
英文:

Specify struct format in json.Marshal()

问题

我有以下的结构体，用于与一个API进行通信：

  1. type Object struct {
  2.     Id         uint64
  3.     Type       string
  4.     Class      string
  5.     Properties []Property
  6. }
  8. type Property struct {
  9.     Name     string
  10.     DataType string
  11.     Value    interface{}
  12. }

在发送之前，我使用json.MarshalIndent()将结构体转换为JSON，得到的结果如下：

  1. {
  2.     "Id": 15,
  3.     "Type": "Node",
  4.     "Class": "Persona",
  5.     "Properties": [
  6.         {
  7.             "Name": "Nombre",
  8.             "DataType": "text",
  9.             "Value": "Oso"
  10.         },
  11.         {
  12.             "Name": "Edad",
  13.             "DataType": "int",
  14.             "Value": 45
  15.         },
  16.         {
  17.             "Name": "Fecha de Naciemiento",
  18.             "DataType": "date",
  19.             "Value": "1989-09-27T05:30:08-06:00"
  20.         }
  21.     ]
  22. }

我想在进行编组之前格式化Value的值（因为它是interface{}类型，所以需要根据值的类型进行格式化）。

我想到的第一个解决方案是创建一个(Object) encode() string函数或类似的函数，遍历[]Property并格式化值，然后分别对每个属性进行编组，然后使用[]string重建Object，然后对对象进行编组。

是否有内置的方法可以实现这个？如果没有，是否有惯用的方法可以实现这个？

英文:

I have the following structs, which I use to communicate with an API:

  1. type Object struct {
  2. 	Id         uint64
  3. 	Type       string
  4. 	Class      string
  5. 	Properties []Property
  6. }
  8. type Property struct {
  9. 	Name     string
  10. 	DataType string
  11. 	Value    interface{}
  12. }

And I use json.MarshalIndent() to convert my struct into a json before sending it. this gives me something like:

  1. {
  2.        "Id": 15,
  3.        "Type": "Node",
  4.        "Class": "Persona",
  5.        "Properties": [
  6.                {
  7.                        "Name": "Nombre",
  8.                        "DataType": "text",
  9.                        "Value": "Oso"
  10.                },
  11.                {
  12.                        "Name": "Edad",
  13.                        "DataType": "int",
  14.                        "Value": 45
  15.                },
  16.                {
  17.                        "Name": "Fecha de Naciemiento",
  18.                        "DataType": "date",
  19.                        "Value": "1989-09-27T05:30:08-06:00"
  20.                }
  21.        ]
  22. }

I want to format the value value (because it is of type interface{} I need to format it depending on the value type) of the struct Property before marshaling it.

The first solution that occurred to me was to create a (Object) encode() string function or something, that iterates through []Property formatting the values, and marshaling each property separately, then reconstructing the Object with an []string instead of the []Property and then marshaling the object.

Is there any built-in way of doing this? If not, is there any idiomatic way of doing it?

答案1

得分: 1

JSON编码器根据值的实际类型对interface{}值进行编码。你可以通过几种方式来覆盖默认的编码方式。

第一种方式是创建一个包装器来控制值的编码方式，使用Marshaler接口。下面是一个改变整数编码方式的包装器示例：

  1. type Value struct{ Value interface{} }
  3. func (v Value) MarshalJSON() ([]byte, error) {
  4.     switch v := v.Value.(type) {
  5.     case int:
  6.         return []byte(fmt.Sprintf("\"#%d\"", v)), nil
  7.     default:
  8.         return json.Marshal(v)
  9.     }
  10. }

使用方法如下：

  1. prop.Value = Value{45}

playground

第二种方式是在Property类型上实现Marshaler，以覆盖整个属性（包括Value字段）的编码方式。

  1. func (p Property) MarshalJSON() ([]byte, error) {
  2.     var buf bytes.Buffer
  3.     buf.WriteString(`{"Name":`)
  4.     d, err := json.Marshal(p.Name)
  5.     if err != nil {
  6.         return nil, err
  7.     }
  8.     buf.Write(d)
  9.     buf.WriteString(`,"DataType":`)
  10.     d, err = json.Marshal(p.DataType)
  11.     if err != nil {
  12.         return nil, err
  13.     }
  14.     buf.Write(d)
  15.     buf.WriteString(`, "Value":`)
  16.     switch v := p.Value.(type) {
  17.     case int:
  18.         fmt.Fprintf(&buf, "\"#%d\"", v)
  19.     default:
  20.         d, err := json.Marshal(v)
  21.         if err != nil {
  22.             return nil, err
  23.         }
  24.         buf.Write(d)
  25.     }
  26.     buf.WriteString("}")
  27.     return buf.Bytes(), nil
  28. }

playground

英文:

The JSON encoder marshals interface{} values according to the actual type of the value. You can override the default encoding in a couple of ways.

The first is to create a wrapper around values to control how they are encoded using the Marshaler interface. Here's a wrapper that changes how integers are encoded:

  1. type Value struct{ Value interface{} }
  3. func (v Value) MarshalJSON() ([]byte, error) {
  4.   switch v := v.Value.(type) {
  5.   case int:
  6. 	return []byte(fmt.Sprintf("\"#%d\"", v)), nil
  7.   default:
  8. 	return json.Marshal(v)
  9.   }
  10. }

Use it like this:

  1. prop.Value = Value{45}

<kbd>playground</kbd>

A second approach is to implement the Marshaler on the Property type to override how all of the property is marshaled including the Value field.

  1. func (p Property) MarshalJSON() ([]byte, error) {
  2.   var buf bytes.Buffer
  3.   buf.WriteString(`{&quot;Name&quot;:`)
  4.   d, err := json.Marshal(p.Name)
  5.   if err != nil {
  6. 	return nil, err
  7.   }
  8.   buf.Write(d)
  9.   buf.WriteString(`,&quot;DataType&quot;:`)
  10.   d, err = json.Marshal(p.DataType)
  11.   if err != nil {
  12. 	return nil, err
  13.   }
  14.   buf.Write(d)
  15.   buf.WriteString(`, &quot;Value&quot;:`)
  16.   switch v := p.Value.(type) {
  17.   case int:
  18. 	fmt.Fprintf(&amp;buf, &quot;\&quot;#%d\&quot;&quot;, v)
  19.   default:
  20. 	d, err := json.Marshal(v)
  21. 	if err != nil {
  22. 		return nil, err
  23. 	}
  24. 	buf.Write(d)
  25.   }
  26.   buf.WriteString(&quot;}&quot;)
  27.   return buf.Bytes(), nil
  28. }

<kbd>playground</kbd>

huangapple
  • 本文由 发表于 2014年10月3日 05:33:40
  • 转载请务必保留本文链接：https://go.coder-hub.com/26170007.html
  • format
  • go
  • json
  • marshalling
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