Golang中如何从嵌套JSON解析并填充嵌套结构体

在 Bond 的 UnmarshalJSON 方法中，你忘记将 aux.Cashflow 赋值给 (*u).Cashflow。这是导致 Cashflow 为空切片的原因。

以下是修正后的 Bond.UnmarshalJSON 方法：

func (u *Bond) UnmarshalJSON(p []byte) error {
	var aux struct {
		ID        string  `json:"ID"`
		Ticker    string  `json:"ticker"`
		IssueDate string  `json:"issueDate"`
		Maturity  string  `json:"maturity"`
		Coupon    float64 `json:"coupon"`
		Cashflow  []Flujo `json:"cashFlow"`
	}

	err := json.Unmarshal(p, &aux)
	if err != nil {
		return err
	}

	t, err := time.Parse(dateFormat, aux.IssueDate)
	if err != nil {
		return err
	}
	y, err := time.Parse(dateFormat, aux.Maturity)
	if err != nil {
		return err
	}
	(*u).ID = aux.ID
	(*u).Ticker = aux.Ticker
	(*u).IssueDate = t
	(*u).Maturity = y
	(*u).Coupon = aux.Coupon
	(*u).Cashflow = aux.Cashflow // 添加这一行
	return nil
}

另外，JSON 字段标签中的 "id" 应该改为 "ID" 以匹配 JSON 数据中的大写键名。修正后的完整示例如下：

package main

import (
	"encoding/json"
	"fmt"
	"time"
)

const data = `[
    {
        "ID": "1",
        "ticker": "GD30",
        "issueDate": "2020-01-01",
        "maturity": "2030-07-09",
        "coupon": 0.05,
        "cashFlow": [
            {   "date": "2021-01-09",
                "rate": 0.00125,
                "amortization": 0,
                "residual": 1,
                "amount": 0},
            {   "date": "2021-07-09",
                "rate": 0.00125,
                "amortization": 0,
                "residual": 1,
                "amount": 0},
            {   "date": "2022-01-09",
                "rate": 0.005,
                "amortization": 0,
                "residual": 1,
                "amount": 0}]
        }
]`

type Flujo struct {
	Date     time.Time
	Rate     float64
	Amort    float64
	Residual float64
	Amount   float64
}

type Bond struct {
	ID        string
	Ticker    string
	IssueDate time.Time
	Maturity  time.Time
	Coupon    float64
	Cashflow  []Flujo
}

const dateFormat = "2006-01-02"

var Bonds []Bond

func (c *Flujo) UnmarshalJSON(p []byte) error {
	var aux struct {
		Date     string  `json:"date"`
		Rate     float64 `json:"rate"`
		Amort    float64 `json:"amortization"`
		Residual float64 `json:"residual"`
		Amount   float64 `json:"amount"`
	}
	err := json.Unmarshal(p, &aux)
	if err != nil {
		return err
	}

	t, err := time.Parse(dateFormat, aux.Date)
	if err != nil {
		return err
	}
	c.Date = t
	c.Rate = aux.Rate
	c.Amort = aux.Amort
	c.Residual = aux.Residual
	c.Amount = aux.Amount
	return nil
}

func (u *Bond) UnmarshalJSON(p []byte) error {
	var aux struct {
		ID        string  `json:"ID"`
		Ticker    string  `json:"ticker"`
		IssueDate string  `json:"issueDate"`
		Maturity  string  `json:"maturity"`
		Coupon    float64 `json:"coupon"`
		Cashflow  []Flujo `json:"cashFlow"`
	}

	err := json.Unmarshal(p, &aux)
	if err != nil {
		return err
	}

	t, err := time.Parse(dateFormat, aux.IssueDate)
	if err != nil {
		return err
	}
	y, err := time.Parse(dateFormat, aux.Maturity)
	if err != nil {
		return err
	}
	u.ID = aux.ID
	u.Ticker = aux.Ticker
	u.IssueDate = t
	u.Maturity = y
	u.Coupon = aux.Coupon
	u.Cashflow = aux.Cashflow
	return nil
}

func main() {
	err := json.Unmarshal([]byte(data), &Bonds)
	if err != nil {
		fmt.Println("error:", err)
	}
	fmt.Printf("Bonds: %+v\n", Bonds)
	fmt.Printf("Cashflow: %+v\n", Bonds[0].Cashflow)
}

现在输出会正确显示嵌套的 Cashflow 数据：

Bonds: [{ID:1 Ticker:GD30 IssueDate:2020-01-01 00:00:00 +0000 UTC Maturity:2030-07-09 00:00:00 +0000 UTC Coupon:0.05 Cashflow:[{Date:2021-01-09 00:00:00 +0000 UTC Rate:0.00125 Amort:0 Residual:1 Amount:0} {Date:2021-07-09 00:00:00 +0000 UTC Rate:0.00125 Amort:0 Residual:1 Amount:0} {Date:2022-01-09 00:00:00 +0000 UTC Rate:0.005 Amort:0 Residual:1 Amount:0}]}]
Cashflow: [{Date:2021-01-09 00:00:00 +0000 UTC Rate:0.00125 Amort:0 Residual:1 Amount:0} {Date:2021-07-09 00:00:00 +0000 UTC Rate:0.00125 Amort:0 Residual:1 Amount:0} {Date:2022-01-09 00:00:00 +0000 UTC Rate:0.005 Amort:0 Residual:1 Amount:0}]