怎样用Golang实现规格模式 构建灵活可组合的业务过滤逻辑

Specification

IsSatisfiedBy

package main

import "fmt"

// User 是我们业务中需要被过滤的对象
type User struct {
    ID     string
    Name   string
    Age    int
    Status string // e.g., "active", "inactive", "pending"
}

// Specification 接口定义了检查一个对象是否满足特定条件的方法
type Specification interface {
    IsSatisfiedBy(user User) bool
}

// AgeGreaterThanSpecification 检查用户年龄是否大于某个值
type AgeGreaterThanSpecification struct {
    Age int
}

func (s AgeGreaterThanSpecification) IsSatisfiedBy(user User) bool {
    return user.Age > s.Age
}

// UserStatusSpecification 检查用户状态是否匹配
type UserStatusSpecification struct {
    Status string
}

func (s UserStatusSpecification) IsSatisfiedBy(user User) bool {
    return user.Status == s.Status
}

// AndSpecification 组合多个规格，要求所有规格都满足
type AndSpecification struct {
    Specs []Specification
}

func (s AndSpecification) IsSatisfiedBy(user User) bool {
    for _, spec := range s.Specs {
        if !spec.IsSatisfiedBy(user) {
            return false
        }
    }
    return true
}

// OrSpecification 组合多个规格，要求至少一个规格满足
type OrSpecification struct {
    Specs []Specification
}

func (s OrSpecification) IsSatisfiedBy(user User) bool {
    for _, spec := range s.Specs {
        if spec.IsSatisfiedBy(user) {
            return true
        }
    }
    return false
}

// NotSpecification 对一个规格取反
type NotSpecification struct {
    Spec Specification
}

func (s NotSpecification) IsSatisfiedBy(user User) bool {
    return !s.Spec.IsSatisfiedBy(user)
}

func main() {
    users := []User{
        {ID: "1", Name: "Alice", Age: 25, Status: "active"},
        {ID: "2", Name: "Bob", Age: 30, Status: "inactive"},
        {ID: "3", Name: "Charlie", Age: 20, Status: "active"},
        {ID: "4", Name: "David", Age: 35, Status: "pending"},
    }

    // 查找年龄大于28岁且状态为"active"的用户
    ageSpec := AgeGreaterThanSpecification{Age: 28}
    activeSpec := UserStatusSpecification{Status: "active"}
    combinedSpec := AndSpecification{Specs: []Specification{ageSpec, activeSpec}}

    fmt.Println("年龄大于28岁且状态为'active'的用户:")
    for _, user := range users {
        if combinedSpec.IsSatisfiedBy(user) {
            fmt.Printf("- %s (ID: %s, Age: %d, Status: %s)\n", user.Name, user.ID, user.Age, user.Status)
        }
    }
    // 预期输出: - Bob (ID: 2, Age: 30, Status: inactive) -- 实际不会，因为Bob状态是inactive
    // 预期输出: (无，因为没有用户同时满足这两个条件)

    fmt.Println("\n年龄大于28岁或状态为'active'的用户:")
    orSpec := OrSpecification{Specs: []Specification{ageSpec, activeSpec}}
    for _, user := range users {
        if orSpec.IsSatisfiedBy(user) {
            fmt.Printf("- %s (ID: %s, Age: %d, Status: %s)\n", user.Name, user.ID, user.Age, user.Status)
        }
    }
    // 预期输出:
    // - Alice (ID: 1, Age: 25, Status: active)
    // - Bob (ID: 2, Age: 30, Status: inactive)
    // - Charlie (ID: 3, Age: 20, Status: active)

    fmt.Println("\n非活跃状态的用户:")
    notActiveSpec := NotSpecification{Spec: activeSpec}
    for _, user := range users {
        if notActiveSpec.IsSatisfiedBy(user) {
            fmt.Printf("- %s (ID: %s, Age: %d, Status: %s)\n", user.Name, user.ID, user.Age, user.Status)
        }
    }
    // 预期输出:
    // - Bob (ID: 2, Age: 30, Status: inactive)
    // - David (ID: 4, Age: 35, Status: pending)
}

if-else if-else