处理定制BSON Marshaling（Golang& mgo）

问题描述

我有一些需要自定义编组的结构。当我测试时，我使用JSON和标准的JSON编组器。由于它不编码未导出的字段，因此我需要编写一个自定义的MarshalJSON函数，该函数完美运行。当我在包含那些需要自定义编组的字段的父结构体上调用json.Marshal时，它运行正常。

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.

现在我需要为一些MongoDB编组一切到BSON工作，而且我找不到有关如何编写自定义BSON编组的任何文档。任何人都可以告诉我如何为我在下面演示的BSON / mgo做同样的事情？

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 （重要部分）

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 （同样，只是相关的部分）

product.go (again, just the relevant parts)

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

当我调用json.Marshal（p），其中p是一个Product时，它会生成我想要的输出，而不需要该模式（不确定名称）在哪里创建一个结构，它只是一个包含所有导出在我看来，使用我使用的内联方法大大简化了API，并且阻止了额外的结构混乱。

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.

$ b

推荐答案

自定义bson编组/解组以几乎相同的方式工作，您必须实施和接口

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

类似这样的东西应该可以工作：

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,
    }
}

// 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
    }
}

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