过滤器模式

过滤器模式

过滤器模式(Filter Pattern)或标准模式(Criteria Pattern)是一种设计模式,这种模式允许开发人员使用不同的标准来过滤一组对象,通过逻辑运算以解耦的方式把它们连接起来。这种类型的设计模式属于结构型模式,它结合多个标准来获得单一标准。

意图

对同一组对象能够以不同过滤条件筛选出来

主要解决

能够以不同条件或条件的组合筛选对象

何时使用

一组对象需要根据属性作筛选时

如何解决

使用过滤器类进行筛选

应用实例
  1. 对用户信息根据不同条件如性别、婚姻状况筛选
  2. 对车辆根据根据不同条件如颜色、款式筛选
优点

能使用不同过滤器的组合方便的筛选对象

缺点

过滤器依赖对象的结构,对象属性变化时过滤器也需要变化,如示例中的婚姻状况增加了一种"离异",则需要增加或修改过滤器

注意事项

过滤器应该尽量简单,复杂的过滤器应使用多个简单过滤器组合得到,这样当对象属性变化时,过滤器的改动能尽量小

示例

整理用户信息时,使用过滤器方便的筛选不同条件的人,比如筛选男性、女性、单身女性等等
在这里插入图片描述

#include "pch.h"
#include <iostream>
#include <sstream>
#include <vector>
#include <algorithm>

// 人
class Person
{
public:
    Person(int ID, std::string name, std::string gender, std::string maritalStatus)
    {
        if ("Male" != gender && "Female" != gender) { throw "Invalid Parameter"; }
        if ("Single" != maritalStatus && "Married" != maritalStatus) { throw "Invalid Parameter"; }

        this->ID = ID;
        this->name = name;
        this->gender = gender;
        this->maritalStatus = maritalStatus;
    }

    std::string GetName()
    {
        return this->name;
    }

    std::string GetGender()
    {
        return this->gender;
    }

    std::string GetMaritalStatus()
    {
        return this->maritalStatus;
    }

    std::string Info()
    {
        std::string info;
        std::ostringstream ostr;
        ostr << "Person : [Name : " << name << ", Gender : " << gender << ", Marital Status : " << maritalStatus << "]";
        return ostr.str();
    }

    bool operator == (const Person & person) const
    {
        return this->ID == person.ID;
    }

    bool operator < (const Person & person) const
    {
        return this->ID < person.ID;
    }

private:
    int ID;
    std::string name;
    std::string gender;
    std::string maritalStatus;
};

class ICriteria
{
public:
    virtual std::vector<Person> meetCriteria(const std::vector<Person>& persons) = 0;
};

// 过滤为男性
class MaleCriteria : public ICriteria
{
public:
    virtual std::vector<Person> meetCriteria(const std::vector<Person>& persons)
    {
        std::vector<Person> resPersons;
        for (Person p : persons)
        {
            if (p.GetGender() == "Male")
            {
                resPersons.push_back(p);
            }
        }
        return resPersons;
    }
};

// 过滤为女性
class FemaleCriteria : public ICriteria
{
public:
    virtual std::vector<Person> meetCriteria(const std::vector<Person>& persons)
    {
        std::vector<Person> resPersons;
        for (Person p : persons)
        {
            if (p.GetGender() == "Female")
            {
                resPersons.push_back(p);
            }
        }
        return resPersons;
    }
};

// 过滤为已婚
class MaritalCriteria : public ICriteria
{
public:
    virtual std::vector<Person> meetCriteria(const std::vector<Person>& persons)
    {
        std::vector<Person> resPersons;
        for (Person p : persons)
        {
            if (p.GetMaritalStatus() == "Married")
            {
                resPersons.push_back(p);
            }
        }
        return resPersons;
    }
};

// 过滤为单身
class SingleCriteria : public ICriteria
{
public:
    virtual std::vector<Person> meetCriteria(const std::vector<Person>& persons)
    {
        std::vector<Person> resPersons;
        for (Person p : persons)
        {
            if (p.GetMaritalStatus() == "Single")
            {
                resPersons.push_back(p);
            }
        }
        return resPersons;
    }
};

// 与过滤器
class AndCriteria : public ICriteria
{
public:
    AndCriteria(ICriteria* pCriteriaA, ICriteria* pCriteriaB)
    {
        this->pCriteriaA = pCriteriaA;
        this->pCriteriaB = pCriteriaB;
    }

    ~AndCriteria()
    {
        delete pCriteriaA;
        pCriteriaA = nullptr;

        delete pCriteriaB;
        pCriteriaB = nullptr;
    }

    virtual std::vector<Person> meetCriteria(const std::vector<Person>& persons)
    {
        std::vector<Person> resPersons = pCriteriaA->meetCriteria(pCriteriaB->meetCriteria(persons));
        return resPersons;
    }

private:
    ICriteria* pCriteriaA;
    ICriteria* pCriteriaB;
};

// 或过滤器
class OrCriteria : public ICriteria
{
public:
    OrCriteria(ICriteria* pCriteriaA, ICriteria* pCriteriaB)
    {
        this->pCriteriaA = pCriteriaA;
        this->pCriteriaB = pCriteriaB;
    }

    ~OrCriteria()
    {
        delete pCriteriaA;
        pCriteriaA = nullptr;

        delete pCriteriaB;
        pCriteriaB = nullptr;
    }

    virtual std::vector<Person> meetCriteria(const std::vector<Person>& persons)
    {
        std::vector<Person> resPersonsA = pCriteriaA->meetCriteria(persons);
        std::vector<Person> resPersonsB = pCriteriaB->meetCriteria(persons);
        std::vector<Person> resPersons;
        std::set_union(resPersonsA.begin(), resPersonsA.end(),
                       resPersonsB.begin(), resPersonsB.end(), std::back_inserter(resPersons));
        return resPersons;
    }

private:
    ICriteria* pCriteriaA;
    ICriteria* pCriteriaB;
};

// 调用示例
int main()
{
    std::vector<Person> persons;
    persons.push_back(Person(1, "Bob", "Male", "Single"));
    persons.push_back(Person(2, "Amy", "Female", "Married"));
    persons.push_back(Person(3, "Mike", "Male", "Single"));
    persons.push_back(Person(4, "Jhon", "Male", "Single"));
    persons.push_back(Person(5, "Jimy", "Male", "Married"));
    persons.push_back(Person(6, "Anna", "Female", "Single"));
    persons.push_back(Person(7, "Alice", "Female", "Married"));
    persons.push_back(Person(8, "Sue", "Female", "Single"));
    persons.push_back(Person(9, "Jane", "Female", "Married"));
    persons.push_back(Person(10, "Nancy", "Female", "Single"));

    // 筛选男性
    ICriteria* maleCriteria = new MaleCriteria();
    std::vector<Person> males = maleCriteria->meetCriteria(persons);
    std::cout << "Males:" << std::endl;
    for (Person p : males)
    {
        std::cout << p.Info() << std::endl;
    }

    // 筛选单身女性
    ICriteria* singleFemaleCriteria = new AndCriteria(new FemaleCriteria(), new SingleCriteria());
    std::vector<Person> singleFemales = singleFemaleCriteria->meetCriteria(persons);
    std::cout << "Single FeMales:" << std::endl;
    for (Person p : singleFemales)
    {
        std::cout << p.Info() << std::endl;
    }
}
>>>
Males:
Person : [Name : Bob, Gender : Male, Marital Status : Single]
Person : [Name : Mike, Gender : Male, Marital Status : Single]
Person : [Name : Jhon, Gender : Male, Marital Status : Single]
Person : [Name : Jimy, Gender : Male, Marital Status : Married]
Single FeMales:
Person : [Name : Anna, Gender : Female, Marital Status : Single]
Person : [Name : Sue, Gender : Female, Marital Status : Single]
Person : [Name : Nancy, Gender : Female, Marital Status : Single]
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