Records : 420
Scenario : Use MyBatis's <resultMap></resultMap> to manually specify the query result object properties, types and database table field properties and types in one-to-one correspondence. Use the properties property, javaType, jdbcType, column of <result></result> to complete the corresponding relationship. Use the resultMap attribute reference of tags such as <select>.
Versions : JDK 1.8, Spring Boot 2.6.3, mybatis-3.5.9.
1. Basic knowledge
1.1 MyBatis label
(1) View the tags supported by MyBatis
Address: http://mybatis.org/dtd/mybatis-3-mapper.dtd
(2) View label usage
Take the <mapper></mapper> tag element as an example, as follows in mybatis-3-mapper.dtd:
<!ELEMENT mapper (cache-ref | cache | resultMap* | parameterMap* | sql* | insert* | update* | delete* | select* )+>
<!ATTLIST mapper
namespace CDATA #IMPLIED
><!ELEMENT mapper(...)+>, indicating that this is a label element mapper.
(..|insert*|update* | delete* | select*), indicating the list of elements that can be nested in the mapper element.
<!ATTLIST mapper>, indicating that this is a supported attribute of an element tag.
1.2 Use of MyBatis
(1) Configure the location of the xml file mapped by mybatis in the application.yml configuration file.
mybatis:
mapper-locations: classpath*:mapper/**/*.xml(2) Create a Java interface. Add methods to the interface.
(3) Create a Java interface mapping xml file. Use the namespace attribute of the <mapper></mapper> tag in xml to specify the full path of the Java interface. The Java interface and the xml mapping file complete the binding relationship.
(4) In the <mapper></mapper> tag, use the id attribute of the tags such as <insert><update><delete><select> to specify the Java method name. The method of the Java interface and the tags inside the <mapper></mapper> of the xml mapping file complete the binding relationship.
2. Use the <resultMap></resultMap> tag element
Scenario : The <resultMap></resultMap> tag element is defined in <mapper></mapper>. Use the resultMap attribute reference in tag elements such as <insert><update><delete><select>.
2.1 Java interface
@Repository
public interface Label05ResultMapMapper {
List<CityLabelPO> queryCity01(CityLabelPO cityPO);
List<CityLabelPO> queryCity02(CityLabelPO cityPO);
}2.2 XML file for Java interface mapping
<?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.hub.example.mapper.Label05ResultMapMapper">
<resultMap id="poResult" type="com.hub.example.domain.CityLabelPO">
<result property="cityId" javaType="java.lang.Long" jdbcType="BIGINT" column="CITY_ID"></result>
<result property="cityName" javaType="java.lang.String" jdbcType="VARCHAR" column="CITY_NAME"></result>
<result property="landArea" javaType="java.lang.Double" jdbcType="DOUBLE" column="LAND_AREA"></result>
<result property="population" javaType="java.lang.Long" jdbcType="BIGINT" column="POPULATION"></result>
<result property="gross" javaType="java.lang.Double" jdbcType="DOUBLE" column="GROSS"></result>
<result property="cityDescribe" javaType="java.lang.String" jdbcType="VARCHAR" column="CITY_DESCRIBE"></result>
<result property="dataYear" javaType="java.lang.String" jdbcType="VARCHAR" column="DATA_YEAR"></result>
<result property="updateTime" javaType="java.util.Date" jdbcType="TIMESTAMP" column="UPDATE_TIME"></result>
</resultMap>
<!-- 1.使用resultMap标签封装返回结果对象-->
<select id="queryCity01" resultMap="poResult">
select aa.*
from t_city aa
where aa.CITY_ID = #{cityId}
</select>
<!-- 2.使用resultType属性指定封装结果对象,以及每个属性执行封装属性名称-->
<select id="queryCity02" resultType="com.hub.example.domain.CityLabelPO">
select CITY_ID AS "cityId",
CITY_NAME AS "cityName",
LAND_AREA AS "landArea",
POPULATION AS "population",
GROSS AS "gross",
CITY_DESCRIBE AS "cityDescribe",
DATA_YEAR AS "dataYear",
UPDATE_TIME AS "updateTime"
from t_city aa
where aa.CITY_ID = #{cityId}
</select>
</mapper>2.3 Use resultMap type matching
When using <resultMap></resultMap>, you need to manually match attributes and classes.
(1) Types in the database, you can use the following SQL query
In MySQL:
SELECT
aa.column_name,
aa.data_type
FROM
INFORMATION_SCHEMA.COLUMNS aa
WHERE aa.TABLE_NAME = 't_city'
在Oracle中：
SELECT
aa.COLUMN_NAME,
aa.DATA_TYPE
FROM
user_tab_columns aa
WHERE aa.table_name = 'T_CITY'In Oracle:
SELECT
aa.COLUMN_NAME,
aa.DATA_TYPE
FROM
user_tab_columns aa
WHERE aa.table_name = 'T_CITY'(2) Type in MyBatis
Type in MyBatis: org.apache.ibatis.type.JdbcType.
public enum JdbcType {
ARRAY(2003),
BIT(-7),
TINYINT(-6),
SMALLINT(5),
INTEGER(4),
BIGINT(-5),
FLOAT(6),
REAL(7),
DOUBLE(8),
NUMERIC(2),
DECIMAL(3),
CHAR(1),
VARCHAR(12),
LONGVARCHAR(-1),
DATE(91),
TIME(92),
TIMESTAMP(93),
BINARY(-2),
VARBINARY(-3),
LONGVARBINARY(-4),
NULL(0),
OTHER(1111),
BLOB(2004),
CLOB(2005),
BOOLEAN(16),
CURSOR(-10),
UNDEFINED(-2147482648),
NVARCHAR(-9),
NCHAR(-15),
NCLOB(2011),
STRUCT(2002),
JAVA_OBJECT(2000),
DISTINCT(2001),
REF(2006),
DATALINK(70),
ROWID(-8),
LONGNVARCHAR(-16),
SQLXML(2009),
DATETIMEOFFSET(-155),
TIME_WITH_TIMEZONE(2013),
TIMESTAMP_WITH_TIMEZONE(2014);
public final int TYPE_CODE;
private static Map<Integer, JdbcType> codeLookup = new HashMap();
private JdbcType(int code) {
this.TYPE_CODE = code;
}
public static JdbcType forCode(int code) {
return (JdbcType)codeLookup.get(code);
}
static {
JdbcType[] var0 = values();
int var1 = var0.length;
for(int var2 = 0; var2 < var1; ++var2) {
JdbcType type = var0[var2];
codeLookup.put(type.TYPE_CODE, type);
}
}
}(3) Types in Java entity classes
The type in the Java entity class is directly viewed in the definition object. for example:
java.lang.Integer
java.lang.Long
java.lang.Double
java.lang.String
java.lang.String
java.util.Date
java.lang.Boolean3. Test
3.1 Test code
@Slf4j
@RestController
@RequestMapping("/hub/example/cityLabel")
public class CityLabelController {
@Autowired
private Label05ResultMapMapper label05ResultMapMapper;
@GetMapping("/load05")
public Object load05() {
log.info("测试开始...");
CityLabelPO cityPO = CityLabelPO.builder().cityId(3L).build();
// 示例一
List<CityLabelPO> list01 = label05ResultMapMapper.queryCity01(cityPO);
// 示例二
List<CityLabelPO> list02 = label05ResultMapMapper.queryCity02(cityPO);
log.info("测试结束...");
return "执行成功";
}
}3.2 Test request
URL：http://127.0.0.1:18080/hub-example/hub/example/cityLabel/load05
3.3 Execute SQL
The example uses the <resultMap></resultMap> tag to assemble SQL for different queries according to different conditions to adapt to different business scenarios.
Example one:
select aa.* from t_city aa where aa.CITY_ID = ?Example two:
SELECT
CITY_ID AS "cityId",
CITY_NAME AS "cityName",
LAND_AREA AS "landArea",
POPULATION AS "population",
GROSS AS "gross",
CITY_DESCRIBE AS "cityDescribe",
DATA_YEAR AS "dataYear",
UPDATE_TIME AS "updateTime"
FROM
t_city aa
WHERE aa.CITY_ID = ?4. Support
4.1 Entity objects
(1) Encapsulate the result object CityLabelPO
@Data
@Builder
@NoArgsConstructor
@AllArgsConstructor
public class CityLabelPO {
private Long cityId;
private String cityName;
private Double landArea;
private Long population;
private Double gross;
private String cityDescribe;
private String dataYear;
private Date updateTime;
}4.2 Create table statement
CREATE TABLE t_city (
CITY_ID BIGINT(16) NOT NULL COMMENT '唯一标识',
CITY_NAME VARCHAR(64) COLLATE utf8_bin NOT NULL COMMENT '城市名',
LAND_AREA DOUBLE DEFAULT NULL COMMENT '城市面积',
POPULATION BIGINT(16) DEFAULT NULL COMMENT '城市人口',
GROSS DOUBLE DEFAULT NULL COMMENT '生产总值',
CITY_DESCRIBE VARCHAR(512) COLLATE utf8_bin DEFAULT NULL COMMENT '城市描述',
DATA_YEAR VARCHAR(16) COLLATE utf8_bin DEFAULT NULL COMMENT '数据年份',
UPDATE_TIME DATETIME DEFAULT NULL COMMENT '更新时间'
) ENGINE=INNODB DEFAULT CHARSET=utf8 COLLATE=utf8_bin COMMENT='城市信息表';Above, thanks.
April 23, 2023