MyBatis实现主键返回功能的几种方式

<insert id="insertUser" parameterType="User" useGeneratedKeys="true" keyProperty="id">
    INSERT INTO user (username, email, age)
    VALUES (#{username}, #{email}, #{age})
</insert>

@Options(useGeneratedKeys = true, keyProperty = "id", keyColumn = "id")
@Insert("INSERT INTO user (username, email, age) VALUES (#{username}, #{email}, #{{age})")
int insertUser(User user);

<insert id="insertUser" parameterType="User">
    <selectKey keyProperty="id" resultType="java.lang.Long" order="AFTER">
        SELECT LAST_INSERT_ID()
    </selectKey>
    INSERT INTO user (username, email, age)
    VALUES (#{username}, #{email}, #{age})
</insert>

<insert id="insertUser" parameterType="User">
    <selectKey keyProperty="id" resultType="java.lang.Long" order="BEFORE">
        SELECT user_seq.NEXTVAL FROM DUAL
    </selectKey>
    INSERT INTO user (id, username, email, age)
    VALUES (#{id}, #{username}, #{email}, #{age})
</insert>

@Insert("INSERT INTO user (username, email, age) VALUES (#{username}, #{email}, #{age})")
@SelectKey(statement = "SELECT LAST_INSERT_ID()", keyProperty = "id", 
           resultType = Long.class, before = false)
int insertUser(User user);

public class User {
    private Long id;
    private String username;
    private String email;
    private Integer age;
    
    // 构造方法、getter、setter 省略
}

public interface UserMapper {
    int insertUser(User user);
    
    @Options(useGeneratedKeys = true, keyProperty = "id")
    @Insert("INSERT INTO user (username, email, age) VALUES (#{username}, #{email}, #{age})")
    int insertUserWithAnnotation(User user);
}

// 获取 SqlSession 和 Mapper
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);

// 创建用户对象
User user = new User();
user.setUsername("john_doe");
user.setEmail("john@example.com");
user.setAge(25);

// 执行插入操作
int result = userMapper.insertUser(user);

// 插入成功后，主键会自动回填到 user 对象中
System.out.println("插入成功，生成的主键ID: " + user.getId());

// 此时可以直接使用 user.getId() 进行后续操作

<!-- 复合主键示例 -->
<insert id="insertUser" useGeneratedKeys="true" keyProperty="id,version">
    INSERT INTO user (...) VALUES (...)
</insert>