# Mybatis 常用操作、使用技巧

Mybatis 常用操作、使用技巧

Mybatis Repalce into 判断批量新增或者修改

• Mybatis批量插入的时候判断，根据主键或者唯一索引（组合索引）

• 假如有表t_menu，我们用Mybatis向里面批量添加多条记录的时候，如果表中有唯一性索引（组合索引）。假如t_menu中的唯一性索引为name那么用replace into的时候，当named的值相同的时候，进行更新操作。否则进行插入操作。假如t_menu中有组合唯一索引（name,price）那么只要有一个索引字段的值不同那么进行插入，只有两个都相同的时候进行更新操作。

• Sql如下：

<insert id="addorupdate">
    replace into t_menu (name,price,flavor) values
    <foreach collection="menu" item="item" separator=",">
    (#{item.name},#{item.price},#{item.flavor})
    foreach>
insert>

• 注意用Repalce into的时候必须要有主键或者是索引，索引可以是单个唯一索引，也可以是组合唯一索引。

---

传参String 类型逗号分隔

• dao接口如下，记住得要加上@param，不然xml中分隔的时候会报错，id没有get方法。

List<User> listUsersByIdWithIn(@Param("id") String ids);

• xml中sql 如下

<select id="selectWithIn" resultType="map">
    <foreach collection="id.split(',')" index="index" item="id" open="(" separator="," close=")">
        <if test="(index % 999) ==998"> NUll) or id in (if>'${id}'
    foreach>
select>

---

in 查询 超过1000条 处理

• 当in 查询超过1000时候会出错，动态的拼接in进行查询

<select id="inSelect" resultType="map">
	select * from test where id in
	<foreach collection="list" index="index" item="id" open="(" separator="," close=")">
		<if test="(index % 999) ==998"> NUll) or id in (if>'${id}'
    foreach>
select>

---

insert batch操作

• 批量插入操作

<insert id="insertBatch" parameterType="list">
	insert INTO test (id,name,age) VALUES
    <foreach collection="list" item="item" separator=",">
    	(#{item.id}, #{item.name}, #{dependency.age})
    foreach>
insert>

---

查询结果 Map 接收 key 大小写问题

配置全局的配置 统一大小写

• MapKeyLowerWrapper

public class MapKeyLowerWrapper extends MapWrapper {

    private static final String ORACLE = "oracle";

    public MapKeyLowerWrapper(MetaObject metaObject, Map<String, Object> map) {
        super(metaObject, map);
    }

    @Override
    public String findProperty(String name, boolean useCamelCaseMapping) {
        DruidDataSource dataSource = SpringContextUtils.getBean(DruidDataSource.class);
        String dbType = dataSource.getDbType();
        // Oracle Map 结果中 key转为小写
        if(ORACLE.equalsIgnoreCase(dbType)) {
            return name == null ? "" : name.toLowerCase();
        }
        return name;
    }
}

• MapWrapperFactory

public class MapWrapperFactory implements ObjectWrapperFactory {

    @Override
    public boolean hasWrapperFor(Object object) {
        return object != null && object instanceof Map;
    }

    @Override
    public ObjectWrapper getWrapperFor(MetaObject metaObject, Object object) {
        return new MapKeyLowerWrapper(metaObject,(Map)object);
    }
}

• 配置 ConfigurationCustomizer Bean

/**
  * 创建 MapWrapperFactory 的 Bean 解决 Map 结果中 key 的大小写
  * @return
  */
@Bean
public ConfigurationCustomizer configurationCustomizer() {
    return configuration -> configuration.setObjectWrapperFactory(new MapWrapperFactory());
}

封装对象继承 HashMap 重写 put

• LowerKeyMap

public class LowerKeyMap extends HashMap {

    @Override
    public Object put(Object key, Object value) {
        if (Objects.nonNull(key)) {
            key = key.toString().toLowerCase();
        }
        return super.put(key, value);
    }
}

• UpperKeyMap

public class UpperKeyMap extends HashMap {

    @Override
    public Object put(Object key, Object value) {
        if (Objects.nonNull(key)) {
            key = key.toString().toUpperCase();
        }
        return super.put(key, value);
    }
}

Insert 多 Value 写法

Mysql

• 方式一：注解形式

@Insert("")
 int insertBatch(TestDo testDO);

Oracle

• 方式一：注解形式

@Insert("")
void insertBatch(TestDo testDO);

DatabaseId 的使用

• Mybatis 这个参数标志了当前数据库的标识，使用之前需要配置一下，将对应的标识进行注册，完美支持动态数据源

@Configuration
public class DataBaseConfig {

    private static final Logger logger = LoggerFactory.getLogger(DataBaseConfig.class);

    @Value("${mybatis.mapper-locations}")
    private String mapperLocations;

    @Autowired
    private DruidDataSource dataSource;

    @Bean
    public DatabaseIdProvider databaseIdProvider() {
        DatabaseIdProvider databaseIdProvider = new VendorDatabaseIdProvider();
        Properties properties = new Properties();
        String dbType = dataSource.getDbType();
        properties.setProperty(dbType, dbType.toLowerCase(Locale.ROOT));
        properties.setProperty("Oracle", "oracle");
        properties.setProperty("MySQL", "mysql");
        properties.setProperty("PostgreSQL", "postgresql");
        properties.setProperty("DB2", "db2");
        properties.setProperty("SQL Server", "sqlserver");
        databaseIdProvider.setProperties(properties);
        logger.info("Module:lowcode-database:DatabaseIdProvider bean registered!");
        return databaseIdProvider;
    }

    @Bean
    public SqlSessionFactoryBean sqlSessionFactoryBean(DataSource dataSource) throws Exception {
        SqlSessionFactoryBean factoryBean = new SqlSessionFactoryBean();
        factoryBean.setDataSource(dataSource);
        factoryBean.setDatabaseIdProvider(databaseIdProvider());
        factoryBean.setMapperLocations(new PathMatchingResourcePatternResolver().getResources(mapperLocations));
        logger.info("Module:lowcode-database:SqlSessionFactoryBean bean registered!");
        return factoryBean;
    }
}

• 使用实例 xml：Mybatis 会根据数据源选择不同的 sql执行

<update id="createBCreateTable" databaseId="mysql">
    create table if not exists b_create_table
    (`ID` varchar(36) NOT NULL,
    `SCHEMA` varchar(100) NULL,
    `MODEL` varchar(100) NULL,
    `TABLENAME` varchar(100) NULL,
    `VERSION` varchar(100) NULL,
    `DBTYPE` varchar(100) NULL,
    CONSTRAINT bcreatetable_pk PRIMARY KEY (id))
    ENGINE=InnoDB
    DEFAULT CHARSET=utf8
    COLLATE=utf8_general_ci;
update>
<update id="createBCreateTable" databaseId="postgresql">
    create table if not exists b_create_table
    (`ID` varchar(36) NOT NULL,
    `SCHEMA` varchar(100) NULL,
    `MODEL` varchar(100) NULL,
    `TABLENAME` varchar(100) NULL,
    `VERSION` varchar(100) NULL,
    `DBTYPE` varchar(100) NULL,
    CONSTRAINT bcreatetable_pk PRIMARY KEY (id))
    ENGINE=InnoDB
    DEFAULT CHARSET=utf8
    COLLATE=utf8_general_ci;
update>