C# xaml框架以及Java的ORM介绍

c#有ASP.Net,.NET以及EF Core这几个重要的运行时和框架.分别用于web,应用以及数据库的ORM.

目前跨平台的有Avalonia UI,.Net MAUI以及Uno Platform,至于WPF等本身不是跨平台的,但可以依靠其他库实现跨平台.这里面Avalonia应该是认为bug比较少的.

当然目前最火的跨平台解决方案应该是Flutter,其次是React Native.

至于EF Core,看看代码就知道有多么简洁优雅了.

using var db = new BloggingContext();

// Inserting data into the database
db.Add(new Blog { Url = "http://blogs.msdn.com/adonet" });
db.SaveChanges();

// Querying
var blog = db.Blogs
    .OrderBy(b => b.BlogId)
    .First();

// Updating
blog.Url = "https://devblogs.microsoft.com/dotnet";
blog.Posts.Add(
    new Post
    {
        Title = "Hello World",
        Content = "I wrote an app using EF Core!"
    });
db.SaveChanges();

// Deleting
db.Remove(blog);
db.SaveChanges();

而Java的ORM有Mybatis,Mybatis-plus,Hibernate,Spring Data JPA以及更原始的Jdbctemplate和query dsl.

具体来说,当使用Java和MyBatis编写示例代码时，需要配置MyBatis的环境和数据库连接，并编写映射器接口和SQL映射文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mydatabase"/>
                <property name="username" value="root"/>
                <property name="password" value="password"/>
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper resource="com/example/MyMapper.xml"/>
    </mappers>
</configuration>

package com.example;

public class User {
    private int id;
    private String name;
    private int age;

    // getters and setters
}

import java.util.List;

public interface UserMapper {
    void insertUser(User user);
    void updateUser(User user);
    void deleteUser(int id);
    User getUserById(int id);
    List<User> getAllUsers();
}

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.example.UserMapper">
    <insert id="insertUser" parameterType="com.example.User">
        INSERT INTO users (name, age) VALUES (#{name}, #{age})
    </insert>

    <update id="updateUser" parameterType="com.example.User">
        UPDATE users SET name = #{name}, age = #{age} WHERE id = #{id}
    </update>

    <delete id="deleteUser" parameterType="int">
        DELETE FROM users WHERE id = #{id}
    </delete>

    <select id="getUserById" parameterType="int" resultType="com.example.User">
        SELECT * FROM users WHERE id = #{id}
    </select>

    <select id="getAllUsers" resultType="com.example.User">
        SELECT * FROM users
    </select>
</mapper>

package com.example;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        try {
            // 加载 MyBatis 配置文件
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

            // 创建 SqlSession
            SqlSession sqlSession = sqlSessionFactory.openSession();

            // 获取 UserMapper 接口的实例
            UserMapper userMapper = sqlSession.getMapper(UserMapper.class);

            // 插入用户
            User newUser = new User();
            newUser.setName("John");
            newUser.setAge(25);
            userMapper.insertUser(newUser);
            System.out.println("Inserted user: " + newUser);

            // 更新用户
            User existingUser = userMapper.getUserById(newUser.getId());
            existingUser.setName("John Doe");
            userMapper.updateUser(existingUser);
            System.out.println("Updated user: " + existingUser);

            // 获取所有用户
            List<User> allUsers = userMapper.getAllUsers();
            System.out.println("All users:");
            for (User user : allUsers) {
                System.out.println(user);
            }

            // 删除用户
            userMapper.deleteUser(existingUser.getId());
            System.out.println("Deleted user with ID: " + existingUser.getId());

            // 提交事务
            sqlSession.commit();

            // 关闭 SqlSession
            sqlSession.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

使用MyBatis-Plus编写示例代码时，可以省去编写SQL映射文件，因为MyBatis-Plus提供了便捷的CRUD操作方法和自动生成SQL语句的功能。

package com.example;

import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableName;

@TableName("users")
public class User {
    @TableId(type = IdType.AUTO)
    private Long id;
    private String name;
    private Integer age;

    // getters and setters
}


import com.baomidou.mybatisplus.core.mapper.BaseMapper;

public interface UserMapper extends BaseMapper<User> {
}

package com.example;

import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.baomidou.mybatisplus.core.conditions.update.UpdateWrapper;
import com.baomidou.mybatisplus.core.metadata.IPage;
import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;

@SpringBootApplication
public class Main {
    public static void main(String[] args) {
        // 启动 Spring Boot 应用
        ConfigurableApplicationContext context = SpringApplication.run(Main.class, args);

        // 获取 UserMapper Bean
        UserMapper userMapper = context.getBean(UserMapper.class);

        // 插入用户
        User newUser = new User();
        newUser.setName("John");
        newUser.setAge(25);
        userMapper.insert(newUser);
        System.out.println("Inserted user: " + newUser);

        // 更新用户
        User existingUser = userMapper.selectById(newUser.getId());
        existingUser.setName("John Doe");
        userMapper.updateById(existingUser);
        System.out.println("Updated user: " + existingUser);

        // 查询所有用户
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();
        queryWrapper.orderByAsc("id");
        IPage<User> userPage = userMapper.selectPage(new Page<>(1, 10), queryWrapper);
        System.out.println("All users:");
        for (User user : userPage.getRecords()) {
            System.out.println(user);
        }

        // 删除用户
        userMapper.deleteById(existingUser.getId());
        System.out.println("Deleted user with ID: " + existingUser.getId());

        // 关闭应用上下文
        context.close();
    }
}

使用了MyBatis-Plus的注解 @TableName 来指定实体类与数据库表的映射关系，使用了 @TableId 注解来定义主键字段。UserMapper 接口继承了 BaseMapper<User>，这样就可以直接使用MyBatis-Plus提供的CRUD操作方法。

使用Hibernate编写示例代码时，需要配置Hibernate的环境和数据库连接，并编写实体类和Hibernate映射文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>
        <property name="hibernate.dialect">org.hibernate.dialect.MySQL5Dialect</property>
        <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="hibernate.connection.url">jdbc:mysql://localhost:3306/mydatabase</property>
        <property name="hibernate.connection.username">root</property>
        <property name="hibernate.connection.password">password</property>
        <property name="hibernate.hbm2ddl.auto">update</property>
        <property name="hibernate.show_sql">true</property>
        <mapping resource="com/example/User.hbm.xml"/>
    </session-factory>
</hibernate-configuration>

package com.example;

import javax.persistence.*;

@Entity
@Table(name = "users")
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name = "name")
    private String name;

    @Column(name = "age")
    private Integer age;

    // getters and setters
}

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="com.example.User" table="users">
        <id name="id" column="id">
            <generator class="identity"/>
        </id>
        <property name="name" column="name"/>
        <property name="age" column="age"/>
    </class>
</hibernate-mapping>

package com.example;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;

import java.util.List;

public class Main {
    public static void main(String[] args) {
        // 加载 Hibernate 配置
        Configuration configuration = new Configuration().configure();
        SessionFactory sessionFactory = configuration.buildSessionFactory();

        // 创建 Session
        Session session = sessionFactory.openSession();

        // 开启事务
        Transaction transaction = session.beginTransaction();

        // 插入用户
        User newUser = new User();
        newUser.setName("John");
        newUser.setAge(25);
        session.save(newUser);
        System.out.println("Inserted user: " + newUser);

        // 更新用户
        User existingUser = session.get(User.class, newUser.getId());
        existingUser.setName("John Doe");
        session.update(existingUser);
        System.out.println("Updated user: " + existingUser);

        // 查询所有用户
        List<User> allUsers = session.createQuery("FROM User", User.class).getResultList();
        System.out.println("All users:");
        for (User user : allUsers) {
            System.out.println(user);
        }

        // 删除用户
        session.delete(existingUser);
        System.out.println("Deleted user with ID: " + existingUser.getId());

        // 提交事务
        transaction.commit();

        // 关闭 Session
        session.close();

        // 关闭 SessionFactory
        sessionFactory.close();
    }
}

使用Hibernate的注解 @Entity、@Table、@Id 和 @Column 来定义实体类与数据库表的映射关系和字段信息。Hibernate映射文件 User.hbm.xml 也定义了实体类与数据库表的映射关系。

当使用Spring Data JPA编写示例代码时，可以利用Spring Data JPA提供的接口和方法来进行数据库操作，而无需编写大量的重复代码。

package com.example;

import javax.persistence.*;

@Entity
@Table(name = "users")
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name = "name")
    private String name;

    @Column(name = "age")
    private Integer age;

    // getters and setters
}

import org.springframework.data.jpa.repository.JpaRepository;

public interface UserRepository extends JpaRepository<User, Long> {
}

package com.example;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;

import java.util.List;

@SpringBootApplication
public class Main {
    public static void main(String[] args) {
        // 启动 Spring Boot 应用
        ConfigurableApplicationContext context = SpringApplication.run(Main.class, args);

        // 获取 UserRepository Bean
        UserRepository userRepository = context.getBean(UserRepository.class);

        // 插入用户
        User newUser = new User();
        newUser.setName("John");
        newUser.setAge(25);
        userRepository.save(newUser);
        System.out.println("Inserted user: " + newUser);

        // 更新用户
        User existingUser = userRepository.findById(newUser.getId()).orElse(null);
        existingUser.setName("John Doe");
        userRepository.save(existingUser);
        System.out.println("Updated user: " + existingUser);

        // 查询所有用户
        List<User> allUsers = userRepository.findAll();
        System.out.println("All users:");
        for (User user : allUsers) {
            System.out.println(user);
        }

        // 删除用户
        userRepository.deleteById(existingUser.getId());
        System.out.println("Deleted user with ID: " + existingUser.getId());

        // 关闭应用上下文
        context.close();
    }
}

此外使用JPA与querydsl结合的也很多.QueryDSL仅仅是一个通用的查询框架，专注于通过 JavaAPI 构建类型安全的 Sql 查询

package com.example;

import javax.persistence.*;

@Entity
@Table(name = "users")
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name = "name")
    private String name;

    @Column(name = "age")
    private Integer age;

    // getters and setters
}

package com.example;

import com.querydsl.core.types.dsl.StringExpression;
import com.querydsl.core.types.dsl.StringPath;
import com.querydsl.jpa.impl.JPAQueryFactory;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.querydsl.QuerydslPredicateExecutor;
import org.springframework.stereotype.Repository;

@Repository
public interface UserRepository extends JpaRepository<User, Long>, QuerydslPredicateExecutor<User> {
    // 定义自定义查询方法
    default User findByName(String name) {
        JPAQueryFactory queryFactory = new JPAQueryFactory(getEntityManager());
        QUser user = QUser.user;

        return queryFactory.selectFrom(user)
                .where(user.name.eq(name))
                .fetchOne();
    }

    // 使用Querydsl的字符串表达式进行模糊查询
    default Iterable<User> findByNameLike(String name) {
        JPAQueryFactory queryFactory = new JPAQueryFactory(getEntityManager());
        QUser user = QUser.user;

        StringExpression nameExpression = user.name;

        return queryFactory.selectFrom(user)
                .where(nameExpression.likeIgnoreCase("%" + name + "%"))
                .fetch();
    }
}

package com.example;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;

import java.util.List;

@SpringBootApplication
public class Main {
    public static void main(String[] args) {
        // 启动 Spring Boot 应用
        ConfigurableApplicationContext context = SpringApplication.run(Main.class, args);

        // 获取 UserRepository Bean
        UserRepository userRepository = context.getBean(UserRepository.class);

        // 插入用户
        User newUser = new User();
        newUser.setName("John");
        newUser.setAge(25);
        userRepository.save(newUser);
        System.out.println("Inserted user: " + newUser);

        // 更新用户
        User existingUser = userRepository.findByName("John");
        existingUser.setName("John Doe");
        userRepository.save(existingUser);
        System.out.println("Updated user: " + existingUser);

        // 查询所有用户
        List<User> allUsers = userRepository.findAll();
        System.out.println("All users:");
        for (User user : allUsers) {
            System.out.println(user);
        }

        // 根据名称模糊查询用户
        List<User> usersWithNameLike = userRepository.findByNameLike("John");
        System.out.println("Users with name like 'John':");
        for (User user : usersWithNameLike) {
            System.out.println(user);
        }

        // 删除用户
        userRepository.delete(existingUser);
        System.out.println("Deleted user with ID: " + existingUser.getId());

        // 关闭应用上下文
        context.close();
    }
}