// 接口
public interface UserMapper {
List<User> select(String name,Integer age);
}
xml文件时:
<select id="select" resultType="model.User">
select * from `user` where name = #{arg0} and age =#{arg1}
select>
// or
<select id="select" resultType="model.User">
select * from `user` where name = #{param1} and age =#{param2}
select>
@Insert("INSERT INTO USER(NAME, AGE) VALUES(#{name}, #{age})")
int insert(@Param("name") String name, @Param("age") Integer age);
@Param中定义的name对应了SQL中的#{name},age对应了SQL中的#{age}。
对于insert语句中需要的参数只需要在map中添加同名的key值就可以:
Map<String, Object> map = new HashMap<>();
map.put("name", "CCC");
map.put("age", 40);
userMapper.insertByMap(map);
通过**Map
@Insert("INSERT INTO USER(NAME, AGE) VALUES(#{name,jdbcType=VARCHAR}, #{age,jdbcType=INTEGER})")
int insertByMap(Map<String, Object> map);
由于map的value为Object,即insert语句中需指定参数的数据类型:jdbcType=INTEGER等。
@Insert("INSERT INTO USER(NAME, AGE) VALUES(#{name}, #{age})")
int insertByUser(User user);
#{name}、#{age}就分别对应了User对象中的name和age属性。
xml或注解形式:
当只有一个参数时:使用arg0,param1获得参数是一直有效的。
参数是基本类型:变量名可以随便写,#{id},#{ids},#{123},#{xxgdsgdg},等都可以获得到参数。
参数是javabean:填写Javabean中的属性名
参数是数组:使用array获得参数,再用foreach循环
参数是List:使用list或collection获得参数,再用foreach循环
参数是Set:使用collection获得参数,再用foreach循环
当有多个参数时:
使用argN、paramN或@param定位到某个参数,再灵活使用ognl就ok了。比如#{user.name}、#{users[0].name}
void deleteUserRole(long userId,long[] roleIds);
多个参数时:roleIds是数组,但foreach不能用array。使用参数顺序或@Param。
<foreach collection="arg1" open="(" close=")" separator=" or " item="value">
#{value}
foreach>
<insert id="insert" parameterType="User" useGeneratedKeys="true" keyProperty="id">
insert into user (username,address,email) values (#{username},#{address},#{email})
insert>
@Insert("insert into user (username,address,email) values (#{username},#{address},#{email})")
@Options(useGeneratedKeys = true, keyProperty = "id")
public int insert(User user) throws Exception;
使用@Options注解的userGeneratedKeys 和keyProperty属性,让数据库auto_increment生成的主键值,赋值到keyProperty标记的属性id中;
还有另外一种方法可以获取主键:
<insert id="insert" parameterType="User" >
<selectKey keyProperty="id" order="AFTER" resultType="java.lang.Integer">
select last_insert_id()
selectKey>
insert into user (username,address,email) values (#{username},#{address},#{email})
insert>
@Insert("insert into user (username,address,email) values (#{username},#{address},#{email})")
@SelectKey(statement="select last_insert_id()",keyProperty="id", resultType=int.class, before=true)
public int insert(User user) throws Exception;
@Select("select * from user where id=#{id}")
public User selectById(int id) throws Exception;
@Update("update user set username=#{username},address=#{address},email=#{email} where id=#{id}")
public int update(User user) throws Exception;
@Delete("delete from user where id=#{id}")
public int delete(int id) throws Exception;
Mybatis主要提供这些映射注解:
@Results 用于填写结果集的多个字段的映射关系.
@Result 用于填写结果集的单个字段的映射关系.
@ResultMap 根据ID关联XML里面.
在xml配置文件中,将查询结果和JavaBean属性映射起来的标签是。对应的是@Results注解。
@Results({
@Result(id = true, column = "id", property = "id"),
@Result(column = "username", property = "user_name"),
@Result(column = "city", property = "city") })
@Select("select * from user")
public List<User> selectAll() throws Exception;
@Results({
@Result(id = true, column = "id", property = "id"),
@Result(column = "username", property = "user_name"),
@Result(column = "city", property = "city") })
@Select("select * from user where id=#{id}")
public User selectById(int id) throws Exception;
上面的@Results注解重复使用了。要想使用可以复用的映射器,那么就使用@ResultMap注解。该注解依赖一个xml配置文件。 在接口文件同目录下新建一个userMapper.xml文件,并定义一个名为userMap的resultMap。
<mapper namespace="mapper.UserMapper">
<resultMap id="userMap" type="pojo.User">
<id column="id" property="id" jdbcType="INTEGER" />
<result property="user_name" column="username">result>
<result property="city" column="city">result>
resultMap>
mapper>
在userMapper.java中,使用@ResultMap引用名为userMap的resultMap,实现复用。
@ResultMap("mapper.UserMapper.userMap")
@Select("select * from user where id=#{id}")
public User selectById(int id) throws Exception;
@Select("select * from user")
@ResultMap("mapper.UserMapper.userMap")
public List<User> selectAll() throws Exception;
为了方便演示和免除手工编写映射关系的烦恼,这里提供了一个快速生成映射结果集的方法,具体内容如下:
/**
* 1.用于获取结果集的映射关系
*/
public static String getResultsStr(Class origin) {
StringBuilder stringBuilder = new StringBuilder();
stringBuilder.append("@Results({\n");
for (Field field : origin.getDeclaredFields()) {
String property = field.getName();
//映射关系:对象属性(驼峰)->数据库字段(下划线)
String column = new PropertyNamingStrategy.SnakeCaseStrategy().translate(field.getName()).toUpperCase();
stringBuilder.append(String.format("@Result(property = \"%s\", column = \"%s\"),\n", property, column));
}
stringBuilder.append("})");
return stringBuilder.toString();
}
MyBatis提供了@One注解来配合@Result注解,从而实现一对一关联查询数据的加载。
如:一个用户对应一个账户,User对象中声明Account属性;
@Results({
@Result(id = true, column = "id", property = "id"),
@Result(column = "username", property = "user_name"),
@Result(column = "city", property = "city"),
@Result(column = "account_id", property = "account",one = @One(select = "mapper.AccountMapper.selectById")) })
@Select("select * from user")
public List<User> selectAll() throws Exception;
在这里column = "account_id"是mapper.AccountMapper.selectById方法传递的参数,property = "account"是User对象的account属性。如果@One中SELECT查询返回了多行结果,则会抛出TooManyResultsException异常。
如果结果映射使用的是xml文件,那么可以association 来配置映射:
<mapper namespace="mapper.UserMapper">
<resultMap id="userMapWithAccount" type="pojo.User">
<id column="id" property="id" jdbcType="INTEGER" />
<result property="user_name" column="username">result>
<result property="city" column="city">result>
<association property="account" javaType="Account" column="account_id"
select="mapper.AccountMapper.selectById" />
resultMap>
mapper>
接口如下:
@Select("select * from user")
@ResultMap("mapper.UserMapper.userMapWithAccount")
public List<User> selectAll() throws Exception;
MyBatis提供了@Many注解来配合@Result注解,从而实现一对多关联查询数据的加载。
如:一个讲师对应多个课程,在Tutor里声明courseList属性。
public interface TutorMapper
{
@Results({
@Result(id = true, column = "course_id", property = "courseId"),
@Result(column = "name", property = "name"),
@Result(column = "description", property = "description"),
@Result(column = "start_date" property = "startDate"),
@Result(column = "end_date" property = "endDate")
})
@Select("select * from courses where tutor_id=#{tutorId}")
List<Course> findCoursesByTutorId(int tutorId);
@Results({
@Result(id = true, column = "tutor_id", property = "tutorId"),
@Result(column = "tutor_name", property = "name"),
@Result(column = "email", property = "email"),
@Result(property = "courses", column = "tutor_id",
many = @Many(select = "mappers.TutorMapper.findCoursesByTutorId"))
})
@Select("SELECT tutor_id, name as tutor_name, email, addr_id FROM tutors where tutor_id=#{tutorId}")
Tutor findTutorById(int tutorId);
}
采用配置xml中配置resultMaps的方式,可以用collection来配置映射:
<mapper namespace="mappers.TutorMapper">
<resultMap type="Course" id="CourseResult">
<id column="course_id" property="courseId" />
<result column="name" property="name" />
<result column="description" property="description" />
<result column="start_date" property="startDate" />
<result column="end_date" property="endDate" />
resultMap>
<resultMap type="Tutor" id="TutorResult">
<id column="tutor_id" property="tutorId" />
<result column="tutor_name" property="name" />
<result column="email" property="email" />
<collection property="courses" resultMap="CourseResult" />
resultMap>
mapper>
接口可写成下面:
public interface TutorMapper
{
@Select("SELECT * FROM TUTORS T LEFT JOIN ADDRESSES A ON T.ADDR_ID=A.ADDR_ID LEFT OUTER JOIN COURSES C ON T.TUTOR_ID=C.TUTOR_ID WHERE T.TUTOR_ID=#{tutorId}")
@ResultMap("mappers.TutorMapper.TutorResult")
Tutor selectTutorById(int tutorId);
}
MyBatis提供了各种注解如@InsertProvider,@UpdateProvider,@DeleteProvider和@SelectProvider,来帮助构建动态SQL语句,然后让MyBatis执行这些SQL语句。
以@SelectProvider 为例,主要包含两个注解属性,其中type表示工具类,method 表示工具类的某个方法,用于返回具体的SQL。
@Mapper
public interface UserMapper {
@SelectProvider(type = UserSqlProvider.class, method = "list222")
List<User> list2();
}
工具类代码:
public class UserSqlProvider {
public String list222() {
return "select * from t_user ;
}
<dependencies>
<dependency>
<groupId>org.springframework.bootgroupId>
<artifactId>spring-boot-starter-webartifactId>
dependency>
<dependency>
<groupId>org.mybatis.spring.bootgroupId>
<artifactId>mybatis-spring-boot-starterartifactId>
<version>1.3.1version>
dependency>
<dependency>
<groupId>mysqlgroupId>
<artifactId>mysql-connector-javaartifactId>
<scope>runtimescope>
dependency>
<dependency>
<groupId>org.springframework.bootgroupId>
<artifactId>spring-boot-starter-testartifactId>
<scope>testscope>
dependency>
dependencies>
spring:
datasource:
#连接MySQL
url: jdbc:mysql://localhost:3306/socks?useSSL=false
username: root
password: root
driver-class-name: com.mysql.jdbc.Driver
mybatis:
configuration:
#配置项:开启下划线到驼峰的自动转换. 作用:将数据库字段根据驼峰规则自动注入到对象属性。
map-underscore-to-camel-case: true
logging:
level:
#打印SQL信息
com.hehe.mapper: debug
@Mapper
public interface UserMapper {
/**
* 方式1:使用注解编写SQL。
*/
@Select("select * from t_user")
List<User> list();
/**
* 方式2:使用注解指定某个工具类的方法来动态编写SQL.
*/
@SelectProvider(type = UserSqlProvider.class, method = "listByUsername")
List<User> listByUsername(String username);
/**
* 延伸:上述两种方式都可以附加@Results注解来指定结果集的映射关系.
*
* PS:如果符合下划线转驼峰的匹配项可以直接省略不写。
*/
@Results({
@Result(property = "userId", column = "USER_ID"),
@Result(property = "username", column = "USERNAME"),
@Result(property = "password", column = "PASSWORD"),
@Result(property = "mobileNum", column = "PHONE_NUM")
})
@Select("select * from t_user")
List<User> listSample();
/**
* 延伸:无论什么方式,如果涉及多个参数,则必须加上@Param注解,否则无法使用EL表达式获取参数。
*/
@Select("select * from t_user where username like #{username} and password like #{password}")
User get(@Param("username") String username, @Param("password") String password);
@SelectProvider(type = UserSqlProvider.class, method = "getBadUser")
User getBadUser(@Param("username") String username, @Param("password") String password);
}
/**
* 主要用途:根据复杂的业务需求来动态生成SQL.
*
* 目标:使用Java工具类来替代传统的XML文件.(例如:UserSqlProvider.java <-- UserMapper.xml)
*/
public class UserSqlProvider {
/**
* 方式1:在工具类的方法里,可以自己手工编写SQL。
*/
public String listByUsername(String username) {
return "select * from t_user where username =#{username}";
}
/**
* 方式2:也可以根据官方提供的API来编写动态SQL。
*/
public String getBadUser(@Param("username") String username, @Param("password") String password) {
return new SQL() {
{
SELECT("*");
FROM("t_user");
if (username != null && password != null) {
WHERE("username like #{username} and password like #{password}");
} else {
WHERE("1=2");
}
}}.toString();
}
}
public class User {
private String userId;
private String username;
private String password;
private String mobileNum;
//Getters & Setters
}
官方文档:http://www.mybatis.org/mybatis-3/zh/java-api.html
使用注解配置Mapper:https://blog.csdn.net/soonfly/article/details/67640653
SpringBoot 快速整合Mybatis:https://zhuanlan.zhihu.com/p/31015559
Spring Boot中使用MyBatis注解配置详解:http://blog.didispace.com/mybatisinfo/