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MyBatis 注解和Provider注解(动态构建SQL)使用
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发布时间：2023-02-09

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MyBatis注解配置与动态SQL开发实践

MyBatis是一个强大的 ORM框架，其配置信息可以基于XML文件完成，尤其是在MyBatis 3.x版本中，基于注解的配置方式逐渐成为主流。以下将详细阐述基于注解的MyBatis配置及其在实际项目中的应用。

1. 注解配置简介

在MyBatis中，注解配置是一种简化Mapper接口映射的方式。通过在接口方法上使用MyBatis的注解，可以直接定义SQL语句，或通过ResultMap映射结果集。需要注意的是，注解配置不仅可以与XML配置共存，还可以灵活地根据项目需求进行选择。

1.1 XML配置与注解配置的关系

在mybatis-config.xml文件中，<mappers>元素可以通过以下方式添加注解配置：

或者：

需要注意的是，接口中的一个方法只能选择使用注解或XML映射，不可以同时使用两者。

2. 注解CRUD实例

基于注解的CRUD操作可以显著简化代码编写。以下是一个典型的UserMapper接口示例：

@MappedBean
public interface UserMapper {
    @Select("select id, username, reg_date from t_user where id = #{id}")
    @Results(id = "userResultMap", value = {
        @Result(column = "id", property = "id"),
        @Result(column = "username", property = "username"),
        @Result(column = "reg_date", property = "regDate")
    })
    User getUser(Long id);
    @Select("select * from t_user")
    List
   
     listAll();
    @Select("select * from t_user where id >= #{id} order by ${orderby}")
    List
    
      listByParam(@Param("id") Long id, @Param("orderby") String orderby);
    @Insert("insert into t_user(username, pazzword, salary, reg_date) value (#{username}, #{pazzword}, #{salary}, #{regDate})")
    @Options(useGeneratedKeys = true, keyProperty = "id")
    int insert(User user);
    @Update("update t_user set username = #{username}, reg_date = #{regDate} where id = #{id}")
    int update(User user);
    @Delete("delete from t_user where id = #{id}")
    int delete(@Param("id") Long id);
}
2.1 测试类示例

以下是一个基本的测试类，用于验证注解配置的正确性：

public class App {
    @Test
    public void testGet() throws Exception {
        SqlSession session = MyBatisUtil.getSession();
        UserMapper userMapper = session.getMapper(UserMapper.class);
        User user = userMapper.getUser(3L);
        System.out.println(user);
        session.close();
    }
    @Test
    public void testListAll() throws Exception {
        SqlSession session = MyBatisUtil.getSession();
        UserMapper userMapper = session.getMapper(UserMapper.class);
        List
   
     list = userMapper.listAll();
        list.forEach(user -> {
            System.out.println(user);
        });
        session.close();
    }
    @Test
    public void testListByParam() throws Exception {
        SqlSession session = MyBatisUtil.getSession();
        UserMapper userMapper = session.getMapper(UserMapper.class);
        Map
    
      paramCon = new HashMap<>();
        paramCon.put("GTL_id", "3");
        paramCon.put("LIKES_username", "@");
        List
     
       list = userMapper.listByParam(User.class, paramCon);
        list.forEach(user -> {
            System.out.println(user);
        });
        session.close();
    }
    @Test
    public void testInsert() throws Exception {
        SqlSession session = MyBatisUtil.getSession();
        User user = new User();
        user.setUsername("asda");
        user.setPazzword("123456");
        user.setSalary(new BigDecimal("99.99"));
        user.setRegDate(new Date());
        UserMapper userMapper = session.getMapper(UserMapper.class);
        userMapper.insert(user);
        session.commit();
        System.out.println(user.getId());
        session.close();
    }
    @Test
    public void testUpdate() throws Exception {
        SqlSession session = MyBatisUtil.getSession();
        User user = new User();
        user.setId(6L);
        user.setUsername("asda@");
        user.setRegDate(new Date());
        UserMapper userMapper = session.getMapper(UserMapper.class);
        userMapper.update(user);
        session.commit();
        session.close();
    }
    @Test
    public void testDelete() throws Exception {
        SqlSession session = MyBatisUtil.getSession();
        UserMapper userMapper = session.getMapper(UserMapper.class);
        userMapper.delete(User.class, 7L);
        session.commit();
        session.close();
    }
}

3. Provider注解与动态SQL

Provider注解是一种灵活的SQL构建方式，适用于动态SQL场景。通过自定义Provider类，可以根据需求构建复杂的SQL语句。

3.1 Provider类结构

以下是一个典型的Provider类示例：

public class BaseDaoSqlProvider {
    public String insert(Object bean) {
        Class
    clazz = bean.getClass();
        System.out.println("insert=" + clazz.getName());
        String tableName = "t_" + clazz.getSimpleName();
        SQL sql = new SQL();
        sql.INSERT_INTO(tableName);
        for (Field field : clazz.getDeclaredFields()) {
            field.setAccessible(true);
            String propertyName = field.getName();
            String columnName = propertyName;
            if ("regDate".equals(propertyName)) {
                columnName = "reg_date";
            }
            try {
                if (field.get(bean) != null && !"".equals(field.get(bean))) {
                    sql.VALUES(columnName, "#{" + propertyName + "}");
                }
            } catch (IllegalAccessException e) {
                e.printStackTrace();
            }
        }
        return sql.toString();
    }
    public String update(Object bean) {
        Class
    clazz = bean.getClass();
        System.out.println("update=" + clazz.getName());
        String tableName = "t_" + clazz.getSimpleName();
        SQL sql = new SQL();
        sql.UPDATE(tableName);
        for (Field field : clazz.getDeclaredFields()) {
            field.setAccessible(true);
            String propertyName = field.getName();
            String columnName = propertyName;
            if ("regDate".equals(propertyName)) {
                columnName = "reg_date";
            }
            if ("id".equals(propertyName)) {
                sql.WHERE(columnName + " = #{" + propertyName + "}");
            } else {
                sql.SET(columnName + " = #{" + propertyName + "}");
            }
        }
        return sql.toString();
    }
    public String delete(Class
    clazz) {
        String tableName = "t_" + clazz.getSimpleName();
        SQL sql = new SQL();
        sql.DELETE_FROM(tableName);
        for (Field field : clazz.getDeclaredFields()) {
            field.setAccessible(true);
            String propertyName = field.getName();
            String columnName = propertyName;
            if ("id".equals(propertyName)) {
                sql.WHERE(columnName + " = #{" + propertyName + "}");
            }
        }
        return sql.toString();
    }
    public String get(Class
    clazz) {
        String tableName = "t_" + clazz.getSimpleName();
        SQL sql = new SQL();
        sql.SELECT("*").FROM(tableName);
        for (Field field : clazz.getDeclaredFields()) {
            field.setAccessible(true);
            String propertyName = field.getName();
            String columnName = propertyName;
            if ("id".equals(propertyName)) {
                sql.WHERE(columnName + " = #{" + propertyName + "}");
            }
        }
        return sql.toString();
    }
    public String listAll(Class
    clazz) {
        String tableName = "t_" + clazz.getSimpleName();
        SQL sql = new SQL();
        sql.SELECT("*").FROM(tableName);
        return sql.toString();
    }
    public String listByParam(Class
    clazz, Map
   
     paramCon) {
        String tableName = "t_" + clazz.getSimpleName();
        SQL sql = new SQL();
        sql.SELECT("*").FROM(tableName);
        for (Map.Entry
    
      entry : paramCon.entrySet()) {
            String param = getParamCon(entry.getKey(), entry.getValue());
            if (param != null) {
                sql.WHERE(param);
            }
        }
        return sql.toString();
    }
    private String getParamCon(String key, String value) {
        String[] s = key.split("_");
        if ("LIKES".equals(s[0])) {
            return s[1] + " like '%" + value + "%'";
        }
        if ("EQS".equals(s[0])) {
            return s[1] + " = '" + value + "'";
        }
        if ("EQL".equals(s[0])) {
            return s[1] + " = " + value;
        }
        if ("LTL".equals(s[0])) {
            return s[1] + " <= " + value;
        }
        if ("GTL".equals(s[0])) {
            return s[1] + " >= " + value;
        }
        return null;
    }
}
3.2 UserMapper接口继承BaseDao

以下是一个继承BaseDao接口的UserMapper接口示例：

public interface UserMapper extends BaseDao
   
     {
}
3.3 测试类

以下是一个基于Provider注解的测试类示例：

public class App {
    @Test
    public void testGet() throws Exception {
        SqlSession session = MyBatisUtil.getSession();
        UserMapper userMapper = session.getMapper(UserMapper.class);
        User user = userMapper.get(User.class, 3L);
        System.out.println(user);
        session.close();
    }
    @Test
    public void testListAll() throws Exception {
        SqlSession session = MyBatisUtil.getSession();
        UserMapper userMapper = session.getMapper(UserMapper.class);
        List
   
     list = userMapper.listAll(User.class);
        list.forEach(user -> {
            System.out.println(user);
        });
        session.close();
    }
    @Test
    public void testListByParam() throws Exception {
        SqlSession session = MyBatisUtil.getSession();
        UserMapper userMapper = session.getMapper(UserMapper.class);
        Map
    
      paramCon = new HashMap<>();
        paramCon.put("GTL_id", "3");
        paramCon.put("LIKES_username", "@");
        List
     
       list = userMapper.listByParam(User.class, paramCon);
        list.forEach(user -> {
            System.out.println(user);
        });
        session.close();
    }
    @Test
    public void testInsert() throws Exception {
        SqlSession session = MyBatisUtil.getSession();
        User user = new User();
        user.setUsername("asda");
        user.setPazzword("123456");
        user.setSalary(new BigDecimal("99.99"));
        user.setRegDate(new Date());
        UserMapper userMapper = session.getMapper(UserMapper.class);
        userMapper.insert(user);
        session.commit();
        System.out.println(user.getId());
        session.close();
    }
    @Test
    public void testUpdate() throws Exception {
        SqlSession session = MyBatisUtil.getSession();
        User user = new User();
        user.setId(11L);
        user.setUsername("asda@121");
        user.setSalary(new BigDecimal("98.99"));
        UserMapper userMapper = session.getMapper(UserMapper.class);
        userMapper.update(user);
        session.commit();
        session.close();
    }
    @Test
    public void testDelete() throws Exception {
        SqlSession session = MyBatisUtil.getSession();
        UserMapper userMapper = session.getMapper(UserMapper.class);
        userMapper.delete(User.class, 12L);
        session.commit();
        session.close();
    }
}

4. 总结

通过以上配置和示例，可以看到基于注解的MyBatis配置在实际项目中具有极高的灵活性和可读性。无论是CRUD操作还是动态SQL构建，都可以通过注解和Provider类实现，显著提升开发效率。

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