MyBatis使用简单、灵活,但是有一些特别常用的简单SQL也要手写,很浪费时间。使用通用Mapper后可以免去这种工作,提高开发效率。
pom.xml
)<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter</artifactId>
</dependency>
<dependency>
<groupId>tk.mybatis</groupId>
<artifactId>mapper-spring-boot-starter</artifactId>
<version>2.1.5</version>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.13</version>
</dependency>
spring.datasource.url=jdbc:mysql://localhost:3306/tenmao?useUnicode=true&characterEncoding=UTF8&zeroDateTimeBehavior=convertToNull&serverTimezone=GMT%2B8
spring.datasource.username=tenmao_user
spring.datasource.password=123456
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
Person.java
)@Data
@Table(name = "person")
@NameStyle(Style.camelhumpAndLowercase)
public class Person {
@javax.persistence.Id
@KeySql(useGeneratedKeys = true)
private Integer id;
private String name;
private Integer age;
private Boolean gender;
@ColumnType(jdbcType = JdbcType.VARCHAR, typeHandler = StringListTypeHandler.class)
private List<String> hobbies;
}
PersonMapper.java
)package com.tenmao.tmapper.mapper;
import com.tenmao.tmapper.domain.Person;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;
import tk.mybatis.mapper.common.Mapper;
import java.util.List;
@org.apache.ibatis.annotations.Mapper
public interface PersonMapper extends Mapper<Person> {
@Select("SELECT * FROM person WHERE name=#{name}")
Person selectByName(@Param("name") String name);
List<Person> selectByAge(@Param("age") int age);
}
Person person = personMapper.selectByPrimaryKey(1);
Example example = new Example(Person.class);
example.createCriteria().andGreaterThan("age", 18);
List<Person> people = personMapper.selectByExample(example);
对应的SQL语句是
SELECT id,name,age,gender FROM person WHERE ( ( age > ? ) )
@org.apache.ibatis.annotations.Mapper
public interface PersonMapper extends Mapper<Person> {
@Select("SELECT * FROM person WHERE name=#{name}")
Person selectByName(@Param("name") String name);
}
XML文件方式
mapper/person_mapper.xml
<mapper namespace="com.tenmao.tmapper.mapper.PersonMapper">
<select id="selectByAge" resultType="com.tenmao.tmapper.domain.Person">
SELECT * FROM person WHERE age=#{age}
</select>
</mapper>
application.properties
mybatis.mapper-locations=classpath:mapper/*_mapper.xml
@Transient
private String otherThings; //非数据库表中字段
@ColumnType(typeHandler = AddressTypeHandler.class)
private Address address;
application.properties
mybatis.type-handlers-package=com.tenmao.handler
personMapper.selectByPrimaryKey(1)
执行的SQL语句是Preparing: SELECT id,name,age,gender FROM person WHERE id = ? AND name = ? AND age = ? AND gender = ?
Parameters: 1(Integer), 1(Integer), 1(Integer), 1(Integer)
因为没有配置PrimaryKey,所以在Person的id上配置注解@javax.persistence.Id
@Data
public class Person {
@javax.persistence.Id @GeneratedValue(generator = "JDBC")
private Integer id;
private String name;
private Integer age;
private Boolean gender;
}
提醒:如果实体类中没有一个标记
@Id
的字段,当你使用带有ByPrimaryKey
的方法时,所有的字段会作为联合主键来使用,也就会出现类似where id = ? and countryname = ? and countrycode = ?
的情况。