MyBatis使用说明与总结
MyBatis使用文档
1、开篇两个小知识点
针对MyBatis的配置文件没有提示的解决方案（引入dtd约束）：利用解压缩文件打开
mybatis.jar，解压出来org.apache.ibatis.builder.xml中的两个dtd文件，如http://mybatis.org/dtd/mybatis-3-config.dtd和http://mybatis.org/dtd/mybatis-3-mapper.dtd，选择解压出来的dtd文件，然后重新打开配置文件即可
利用logback在控制台打印sql日志
//在pom.xml引入logback日志依赖
ch.qos.logback
logback-classic
1.2.3
test
//在src/main/resources目录下，引入logback配置文件
"1.0" encoding="UTF-8"?>
"http://ch.qos.logback/xml/ns/logback"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://ch.qos.logback/xml/ns/logback https://raw.githubusercontent.com/enricopulatzo/logback-XSD/master/src/main/xsd/logback.xsd">
"STDOUT" class="ch.qos.logback.core.ConsoleAppender" >
"ch.qos.logback.classic.encoder.PatternLayoutEncoder">
%d{yyyy-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{50}: %msg%n
"com.security.dao" level="DEBUG" />
"INFO">
"STDOUT" />
2、MyBatis的简单测试使用
- MySQL数据库资源配置文件db.properties
url=jdbc:mysql://localhost:3306/spring?characterEncoding=utf-8&allowMultiQueries=true
driver=com.mysql.jdbc.Driver
username=root
password=root- MyBatis全局配置文件
"1.0" encoding="UTF-8" ?>
"-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
"db.properties">
"mapUnderscoreToCamelCase" value="true" />
"lazyLoadingEnabled" value="true" />
"aggressiveLazyLoading" value="false" />
"cacheEnabled" value="true" />
"useGeneratedKeys" value="true" />
<package name="com.security.model" />
default="development">
"development">
"JDBC" />
"POOLED">
"driver" value="${driver}" />
"url" value="${url}" />
"username" value="${username}" />
"password" value="${password}" />
<package name="com.security.dao" />
- 在src/test/java目录下建立JUnit测试类，获取SqlSessionFactory，并且测试使用
public class MyBatisTest {
private SqlSessionFactory sqlSessionFactory;
/**
* 获取SqlSessionFactory
*/
@Before
public void getSessionFactory(){
String resource = "mybatis-config.xml";
try {
InputStream inputStream = Resources.getResourceAsStream(resource);
sqlSessionFactory= new SqlSessionFactoryBuilder().build(inputStream);
} catch (IOException e) {
e.printStackTrace();
}
}
/**
* 测试UserMapper
*/
@Test
public void testUserMapper() {
SqlSession session=sqlSessionFactory.openSession();
UserMapper userMapper=session.getMapper(UserMapper.class);
User user=userMapper.findEntityById(1);
System.out.println(user);
}
}
3、MyBatis参数处理
#{}和${}的区别：#{}是以预编译的形式，将参数设置到sql语句中,PreparedStatement防止sql注入；${}取出的值直接拼装在sql语句中,可能出现安全问题；大多情况下，建议使用#{}，特殊情况除外，如定义结果的排序order by ${}
public List getEmployeeOrderBy(@Param("name")String name);
//sql语句为：select * from Employee order by id desc;
//sql语句为:select * from Employee order by ? desc; - 使用
Insert语句时主键自增长：对于mysql获取自增主键的值，需要在insert方法中利用两个属性：useGeneratedKeys="true"使用自增主键获取主键值策略；keyProperty指定对应的主键属性，也就是mybatis获取到主键值以后，将这个值封装给JavaBean的哪个属性
"addEmployee" parameterType="employee"
useGeneratedKeys="true" keyProperty="id">
insert into employee(name,gender,email) values(#{name},#{gender},#{email});
- 在sql语句中只需要一个参数的情况：mybatis不会做特殊处理，#{参数名/任意名}即可取出参数值
public void add(User user);
"addUser" useGeneratedKeys="true" keyProperty="id" >
insert into user(name,age) values(#{name},#{age})
- 在sql语句中需要两个或者以上参数的情况：
public void addByUserAndAge(String name,int age);
"addByUserAndAge">
insert into user(name,age) values(#{0},#{1})
Or
"addByUserAndAge">
insert into user(name,age) values(#{param1},#{param2})
Or将接口中的方法改为:
public void addByUserAndAge(@Param("name")String name,@Param("age")int age);
"addByUserAndAge">
insert into user(name,age) values(#{name},#{age})
- MyBatis种sql语句多参数处理时会把多个参数封装为一个map，
key：param1...paramN,或者参数的索引也可以；value：传入的参数值#{}就是从map中获取指定的key的值
①public User getUserByMap(Map map);
测试：Map map=new HashMap<>();
map.put("id",1);
map.put("name","冯朗");
System.out.println(mapper.getUserByMap(map));
---------------------------------------------------------------------------
②public Employee getEmp(@Param("id")Integer id,String lastName);
取值：id==>#{id/param1} lastName==>#{param2}
------------------------------------------------------------------------
③public Employee getEmp(Integer id,@Param("e")Employee emp);
取值：id==>#{param1} lastName===>#{param2.lastName/e.lastName}
----------------------------------------------------------------
④##特别注意：如果是Collection（List、Set）类型或者是数组，也会特殊处理。也是把传入的list或者数组封装在map中。
key：Collection（collection）,如果是List还可以使用这个key(list)
数组(array)
public Employee getEmpById(List ids);
取值：取出第一个id的值： #{list[0]} - MyBatis的两个内置参数
_parameter和_databaseId，其中_parameter代表整个参数，当sql方法需要单个参数时_parameter即为该参数，若需要多个参数时，参数会被封装为一个map,_parameter即代表这个map；_databaseId:如果配置了databaseIdProvider标签，则_databaseId就是代表当前数据库的别名
public List getUsersWithParameter(String name);
----------------------------------------------------------------------
public List getUsersWithParameterBean(Map map);
bind和sql标签的使用：bind可以将OGNL表达式的值绑定到一个变量中，方便后来引用这个变量的值；sql用于抽取可重用的片段，方便后期引用，include用于引用已抽取的sql片段
public List getUsersWithBinds(@Param("name")String name);
"selectuser" >
select id,name,age from user
4、MyBatis中的动态SQL
where、if的使用
public List getUserByConditionIf(User user);
trim的使用
public List getUserByConditionTrim(User user);
set的使用
public void updateEmp(User user);
"updateEmp">
update user
<if test="name!=null and !name.equals("")">
name=#{name},
if>
<if test="age!=null">
age=#{age}
if>
id=#{id}
foreach的使用
方式一：
public List getUserByConditionForeach(List list);
- 批量插入数据
public void addByBatch(List list);
"addByBatch">
insert into user(name,age,did) values
"list" item="u" separator=",">
(#{u.name},#{u.age},#{u.department.id})
---------------------------------------------------------------------------------------
方式二：
"saveEmployeeWithForEach" >
"list" item="emp">
insert into employee(name,gender,email,d_id) values(#{emp.name},#{emp.gender},#{emp.email},#{emp.dept.id});
5、MyBatis中的模糊查询
- 常规方式：利用
bind进行数据绑定
public List getEmployeesWithNameLike(@Param("name")String name);
- 利用MyBatis的内置函数
_parameter
public List testInnerParameter(String name);
- 利用MySQL的内置函数
concat(str1,str2,…)
public List getEmployeesWithNameLike(@Param("name")String name);
select * from employee
<if test="name!=null">
name like concat('%',#{name},'%')
if>
- 升级版模糊查询
public List getEmployeeWithUncertainQuery(String query);
6、MyBatis的级联查询
6.1场景一：Employee对应一个Department，查询Employee的同时查询员工对应的部门
- 使用
association进行单步查询，association代表的是一对一关系
"com.security.ben.Employee" id="MyEmp1">
"id" property="id" />
"name" property="name" />
"gender" property="gender" />
"email" property="email" />
"dept" javaType="com.security.ben.Department">
"id" property="id" />
"deptName" property="deptName" />
- 使用
association进行分布查询
"com.security.ben.Employee" id="MyEmp2">
"id" property="id" />
"name" property="name" />
"gender" property="gender" />
"email" property="email" />
"dept" column="d_id" select="com.security.mapper.DepartmentMapper.getDeptById">
6.2场景二：一个Department对应多个Employee，查询部门信息的时候将其多对应的所有员工信息也查询出来
- 使用
collection单步查询，collection代表一对多关系
"com.security.ben.Department" id="SimpleDept">
"id" property="id"/>
"deptName" property="deptName"/>
"emps" ofType="com.security.ben.Employee">
"eid" property="id"/>
"name" property="name"/>
"email" property="email"/>
"gender" property="gender"/>
- 使用
collection进行分步查询
"com.security.ben.Department" id="DifDept">
"id" property="id"/>
"deptName" property="deptName"/>
"emps" select="com.security.mapper.EmployeeMapperPlus.getEmpsByDeptId" column="id" fetchType="lazy">
6.3场景三：用户和角色属于多对多关联关系，参考MyBatis多对多关联查询
- 建立数据表，use和role是多对多的关系，需要采用关联表t_user_role，建立相应的实体类
@Data
@Builder
@NoArgsConstructor
@AllArgsConstructor
public class User implements Serializable {
private static final long serialVersionUID = 1L;
private Integer id;
private String name;
private String email;
private List roles;
}
@Data
@Builder
@NoArgsConstructor
@AllArgsConstructor
public class Role {
private Integer id;
private String name;
private List users;
} - 建立UserMapper和RoleMapper的接口，并定义相应的方法
public interface UserMapper {
public User findUserById(Integer id);
public List findUserByRoleId(Integer roleId);
}
public interface RoleMapper {
public Role findRoleById(Integer id);
public List findRoleByUserId(Integer userId);
} - 建立相应的UserMppaer.xml，并且定义sql语句
"1.0" encoding="UTF-8"?>
"-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
"com.security.dao.UserMapper">
"userMapper" type="user">
"id" property="id" />
"name" property="name" />
"email" property="email" />
"roles" column="id"
select="com.security.dao.RoleMapper.findRoleByUserId">
- 建立相应的RoleMppaer.xml，并且定义sql语句
"1.0" encoding="UTF-8"?>
"-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
"com.security.dao.RoleMapper">
"roleMapper" type="role">
"id" property="id" />
"name" property="name" />
"users" column="id"
select="com.security.dao.UserMapper.findUserByRoleId">
- 多对多关联关系测试
public class MoreToMoreTest {
private SqlSessionFactory sqlSessionFactory;
/**
* 获取SqlSessionFactory
*/
@Before
public void getSessionFactory() {
String resource = "mybatis-config.xml";
try {
InputStream inputStream = Resources.getResourceAsStream(resource);
sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
} catch (IOException e) {
e.printStackTrace();
}
}
@Test
public void testMoreToMore() {
SqlSession session = sqlSessionFactory.openSession();
try {
/*RoleMapper roleMapper = session.getMapper(RoleMapper.class);
Role role = roleMapper.findRoleById(1);
System.out.println(role);*/
UserMapper userMapper=session.getMapper(UserMapper.class);
User user=userMapper.findUserById(2);
System.out.println(user);
} catch (Exception e) {
e.printStackTrace();
} finally {
if (session != null) {
session.close();
}
}
}
}