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 SqlSessionSqlSession 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 SqlSessionsqlSession.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 BeanUserMapper 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 SessionSession 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 Sessionsession.close();// 关闭 SessionFactorysessionFactory.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 BeanUserRepository 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 BeanUserRepository 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();}
}