处理自定义BSON封送处理

问题描述：

I have a number of structs that require custom marshalling. When I was testing I was using JSON and the standard JSON marshaller. As it doesn't marshal unexported fields, I needed to write a custom MarshalJSON function, which worked perfectly. When I called json.Marshal on the parent struct containing the ones that needed custom marshalling as fields, it worked fine.

Now I need to marshal everything to BSON for some MongoDB work, and I can't find any documentation about how to write custom BSON marshalling. Can anyone tell me how to do the equivalent for BSON/mgo for what I've demonstrated below?

currency.go (the important parts)

type Currency struct {
    value        decimal.Decimal //The actual value of the currency.
    currencyCode string          //The ISO currency code.
}

/*
MarshalJSON implements json.Marshaller.
*/
func (c Currency) MarshalJSON() ([]byte, error) {
    f, _ := c.Value().Float64()
    return json.Marshal(struct {
        Value        float64 `json:"value" bson:"value"`
        CurrencyCode string  `json:"currencyCode" bson:"currencyCode"`
    }{
        Value:        f,
        CurrencyCode: c.CurrencyCode(),
    })
}

/*
UnmarshalJSON implements json.Unmarshaller.
*/
func (c *Currency) UnmarshalJSON(b []byte) error {

    decoded := new(struct {
        Value        float64 `json:"value" bson:"value"`
        CurrencyCode string  `json:"currencyCode" bson:"currencyCode"`
    })

    jsonErr := json.Unmarshal(b, decoded)

    if jsonErr == nil {
        c.value = decimal.NewFromFloat(decoded.Value)
        c.currencyCode = decoded.CurrencyCode
        return nil
    } else {
        return jsonErr
    }
}

product.go (again, just the relevant parts)

type Product struct {
    Name  string
    Code  string
    Price currency.Currency
}

When I call json.Marshal(p) where p is a Product, it produces the output I want without the need for the pattern (not sure of the name) where you create a struct which is just a clone with all exported fields.

In my opinion using the inline method I've used greatly simplifies the API and stops you having extra structs that clutter things up.

我有许多需要自定义编组的结构。在测试时，我使用的是JSON和标准的JSON marshaller。由于它不会封送未导出的字段，因此我需要编写一个自定义的MarshalJSON函数，该函数运行良好。当我在包含需要自定义编组的字段的父结构上调用json.Marshal时，它工作正常。 p>

现在，我需要将所有内容封送给BSON进行MongoDB的工作，我找不到有关如何编写自定义BSON编组的任何文档。谁能告诉我如何针对BSON / mgo做与我下面演示的等效的操作？ p>

currency.go strong>（重要部分） p >

  type货币结构{
值十进制。十进制//货币的实际值。
 currencyCode字符串// ISO货币代码。
} 
 
 / *  
MarshalJSON实现json.Marshaller。
 * / 
func（c货币）MarshalJSON（）（[] byte，error）{
f，_：= c.Value（）。Float64（）
返回json.Marshal（  struct {
 Value float64`json：“ value” bson：“ value”`
 CurrencyCode字符串`json：“ currencyCode” bson：“ currencyCode”`
} {
值：f，
 CurrencyCode：c。  CurrencyCode（），
}} 
} 
 
 / * 
UnmarshalJSON实现json.Unmarshaller。
 * / 
func（c * Currency）UnmarshalJSON（b [] byte）错误{
 
解码：  = new（结构{
 Value float64`json：“ value” bson：“ value”`
 CurrencyCode字符串`json：“ currencyCode” bson：“ currencyCode”`
}）
 
 jsonErr  ：= json.Unmarshal（b，已解码）
 
，如果jsonErr == nil {
 c.value =十进制.NewFromFloat（decoded.Value）
 c.currencyCode =已解码.CurrencyCode 
返回nil 
} 否则{
返回jsonErr 
} 
} 
  code>  pre> 
 
   product.go  strong>（同样，只是相关部分） p  > 
 
 
  type产品结构{
名称字符串
代码字符串
价格货币。货币
} 
  code>  pre> 
 
 何时 我叫json.Marshal（p），其中p是一个Product，它将在不需要模式（不确定名称）的情况下生成我想要的输出，在此模式下您将创建一个结构，该结构只是具有所有导出字段的克隆。  p> 
 
 
我认为我使用的内联方法大大简化了API，并阻止了您使用多余的结构使事情变得混乱。 p> 
  div>

答

Custom bson Marshalling/Unmarshalling works nearly the same way, you have to implement the Getter and Setter interfaces respectively

Something like this should work :

type Currency struct {
    value        decimal.Decimal //The actual value of the currency.
    currencyCode string          //The ISO currency code.
}

// GetBSON implements bson.Getter.
func (c Currency) GetBSON() (interface{}, error) {
    f := c.Value().Float64()
    return struct {
        Value        float64 `json:"value" bson:"value"`
        CurrencyCode string  `json:"currencyCode" bson:"currencyCode"`
    }{
        Value:        f,
        CurrencyCode: c.currencyCode,
    }, nil
}

// SetBSON implements bson.Setter.
func (c *Currency) SetBSON(raw bson.Raw) error {

    decoded := new(struct {
        Value        float64 `json:"value" bson:"value"`
        CurrencyCode string  `json:"currencyCode" bson:"currencyCode"`
    })

    bsonErr := raw.Unmarshal(decoded)

    if bsonErr == nil {
        c.value = decimal.NewFromFloat(decoded.Value)
        c.currencyCode = decoded.CurrencyCode
        return nil
    } else {
        return bsonErr
    }
}

处理自定义BSON封送处理

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