Go语言实体检索的惯用模式：包级函数而非“静态方法”

package main

import "fmt"

// Payment 和 User 结构体存在相互引用
type Payment struct {
    ID   int
    User *User
    Amount float64
}

type User struct {
    ID       int
    Name     string
    Payments []*Payment // 修正为 []*Payment
}

// 尝试将 Get 方法定义为接收器方法
func (u *User) Get(id int) *User {
    fmt.Printf("Attempting to get User with ID %d using receiver method.\n", id)
    // 实际逻辑会从数据库或其他数据源获取用户
    if id == 585 {
        return &User{ID: id, Name: "Alice"}
    }
    return nil
}

func (p *Payment) Get(id int) *Payment {
    fmt.Printf("Attempting to get Payment with ID %d using receiver method.\n", id)
    // 实际逻辑会从数据库或其他数据源获取支付信息
    if id == 101 {
        return &Payment{ID: id, Amount: 100.0, User: &User{ID: 585, Name: "Alice"}}
    }
    return nil
}

func main() {
    var u *User // 声明一个 nil User 指针
    user := u.Get(585) // 在 nil 接收器上调用方法
    if user != nil {
        fmt.Printf("Retrieved User: %+v\n", user)
    }

    var p *Payment // 声明一个 nil Payment 指针
    payment := p.Get(101) // 在 nil 接收器上调用方法
    if payment != nil {
        fmt.Printf("Retrieved Payment: %+v\n", payment)
    }
}

package main

import "fmt"

// Payment 和 User 结构体定义不变
type Payment struct {
    ID   int
    User *User
    Amount float64
}

type User struct {
    ID       int
    Name     string
    Payments []*Payment
}

// 惯用的包级函数来检索 User
func GetUser(id int) *User {
    fmt.Printf("Retrieving User with ID %d using package-level function.\n", id)
    // 实际逻辑：从数据库、缓存等数据源获取用户
    if id == 585 {
        return &User{ID: id, Name: "Alice"}
    }
    return nil
}

// 惯用的包级函数来检索 Payment
func GetPayment(id int) *Payment {
    fmt.Printf("Retrieving Payment with ID %d using package-level function.\n", id)
    // 实际逻辑：从数据库、缓存等数据源获取支付信息
    if id == 101 {
        // 假设这里也需要获取关联的用户信息
        user := GetUser(585) // 可以调用其他包级函数
        return &Payment{ID: id, Amount: 100.0, User: user}
    }
    return nil
}

func main() {
    user := GetUser(585)
    if user != nil {
        fmt.Printf("Retrieved User: %+v\n", user)
    }

    payment := GetPayment(101)
    if payment != nil {
        fmt.Printf("Retrieved Payment: %+v\n", payment)
    }
}