标签：ref sso org mit action 支持 tin 信息 ltm
一对一也就是 A 表的一条记录对应 B 表的一条记录，下面的测试数据中，从employee 表来看，一个员工对应一个部门，是一对一关系，如果从部门角度来看，则是一对多的关系，一个部门对应多个员工，本节主要研究一对一的关系。
新建数据表department，有两个字段，插入两条数据如下：
| id | dept_name |
| 1 | CIA |
| 2 | FSB |
新建数据表employee，有三个字段，其中dept_id是外键，关联department表的主键id。插入数据如下：
| id | last_name | dept_id |
| 1 | Tom | 1 |
| 2 | Jerry | 2 |
| 3 | Neo | 1 |
| 4 | Cypher | 2 |
<dependencies> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis</artifactId> <version>3.4.6</version> </dependency> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>5.1.47</version> </dependency> </dependencies>
对于department表，对应实体如下：
package com.yefengyu.mybatis.entity; public class Department { private Integer id; private String deptName; public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getDeptName() { return deptName; } public void setDeptName(String deptName) { this.deptName = deptName; } @Override public String toString() { return "Department{" + "id=" + id + ", deptName=‘" + deptName + ‘\‘‘ + ‘}‘; } }
对于employee表，实体如下，注意在Employee实体中把外键直接变成对于Department对象的引用。
package com.yefengyu.mybatis.entity; public class Employee { private Integer id; private String lastName; private Department department; public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getLastName() { return lastName; } public void setLastName(String lastName) { this.lastName = lastName; } public Department getDepartment() { return department; } public void setDepartment(Department department) { this.department = department; } @Override public String toString() { return "Employee{" + "id=" + id + ", lastName=‘" + lastName + ‘\‘‘ + ", department=" + department + ‘}‘; } }
package com.yefengyu.mybatis.mapper; import com.yefengyu.mybatis.entity.Employee; public interface EmployeeMapper { Employee getEmployee(Integer id); }
根据员工ID查询员工信息和部门信息
一对一查询mapper文件有三种编写方式，分别是：
1、级联属性法
<?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.yefengyu.mybatis.mapper.EmployeeMapper"> <resultMap id="employee" type="com.yefengyu.mybatis.entity.Employee"> <id column="id" property="id"/> <result column="last_name" property="lastName"/> <result column="d_id" property="department.id"/> <result column="dept_name" property="department.deptName"/> </resultMap> <select id="getEmployee" resultMap="employee"> select e.id id, e.last_name last_name, e.dept_id dept_id, d.id d_id,d.dept_name dept_name from employee e, department d where e.id = #{id} and e.dept_id = d.id </select> </mapper>
2、association嵌套结果集
<?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.yefengyu.mybatis.mapper.EmployeeMapper"> <!-- 使用association定义关联的单个对象的封装规则； --> <resultMap id="employee" type="com.yefengyu.mybatis.entity.Employee"> <id column="id" property="id"/> <result column="last_name" property="lastName"/> <!-- association可以指定联合的javaBean对象 property="department"：指定哪个属性是联合的对象 javaType:指定这个属性对象的类型[不能省略] --> <association property="department" javaType="com.yefengyu.mybatis.entity.Department"> <id column="d_id" property="id"/> <result column="dept_name" property="deptName"/> </association> </resultMap> <select id="getEmployee" resultMap="employee"> select e.id id, e.last_name last_name, e.dept_id dept_id, d.id d_id,d.dept_name dept_name from employee e, department d where e.id = #{id} and e.dept_id = d.id </select> </mapper>
3、association分步查询法
1）首先需要创建一个关于department的接口
package com.yefengyu.mybatis.mapper; import com.yefengyu.mybatis.entity.Department; public interface DepartmentMapper { public Department getDeptById(Integer id); }
2）其次编写该接口的映射文件
<?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.yefengyu.mybatis.mapper.DepartmentMapper"> <select id="getDeptById" resultType="com.yefengyu.mybatis.entity.Department"> select id,dept_name from department where id = #{id} </select> </mapper>
3）现在定义一个查询employee的接口（级联属性法和association嵌套结果集测试时已经建立该接口）
package com.yefengyu.mybatis.mapper; import com.yefengyu.mybatis.entity.Employee; public interface EmployeeMapper { Employee getEmployee(Integer id); }
4）编写该接口对应的映射文件
<?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.yefengyu.mybatis.mapper.EmployeeMapper"> <resultMap id="employee" type="com.yefengyu.mybatis.entity.Employee"> <id column="id" property="id"/> <result column="last_name" property="lastName"/> <!-- association定义关联对象的封装规则 select:表明当前属性是调用select指定的方法查出的结果 column:指定将哪一列的值传给这个方法 流程：使用select指定的方法（传入column指定的这列参数的值）查出对象，并封装给property指定的属性 --> <association property="department" select="com.yefengyu.mybatis.mapper.DepartmentMapper.getDeptById" column="dept_id"> </association> </resultMap> <select id="getEmployee" resultMap="employee"> select * from employee where id = #{id} </select> </mapper>
延迟加载：
每次查询Employee对象的时候，都将部门信息一起查询出来。但是想要部门信息在我们使用的时候再去查询，如果不需要就不查询，怎么实现？分步查询的基础上加两个配置：
<!--显示的指定每个我们需要更改的配置的值，即使他是默认的。防止版本更新带来的问题 --> <setting name="lazyLoadingEnabled" value="true"/> <setting name="aggressiveLazyLoading" value="false"/>
Mybatis仅支持association关联对象和collection关联集合对象的延迟加载，association指的就是一对一，collection指的就是一对多查询。
<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd"> <configuration> <settings> <setting name="mapUnderscoreToCamelCase" value="true"/> <setting name="logImpl" value="STDOUT_LOGGING" /> </settings> <environments default="development"> <environment id="development"> <transactionManager type="JDBC"/> <dataSource type="POOLED"> <property name="driver" value="com.mysql.jdbc.Driver"/> <property name="url" value="jdbc:mysql://127.0.0.1:3306/mybatis?characterEncoding=utf8&allowMultiQueries=true"/> <property name="username" value="root"/> <property name="password" value="123456"/> </dataSource> </environment> </environments> <mappers> <mapper resource="mapper/PersonMapper.xml"/> <mapper resource="mapper/EmployeeMapper.xml"/> <mapper resource="mapper/DepartmentMapper.xml"/> </mappers> </configuration>
通用测试代码：
public static void main(String[] args) throws IOException { InputStream resourceAsStream = Resources.getResourceAsStream("mybatis-config.xml"); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream); SqlSession sqlSession = sqlSessionFactory.openSession(); try { EmployeeMapper mapper = sqlSession.getMapper(EmployeeMapper.class); Employee employee = mapper.getEmployee(1); System.out.println(employee); } finally { sqlSession.close(); } }
准对于延迟加载的特殊测试，对于上面测试代码，如果只打印员工名
System.out.println(employee.getLastName());
那么不会查询部门表
Created connection 1776957250. Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@69ea3742] ==> Preparing: select * from employee where id = ? ==> Parameters: 1(Integer) <== Columns: id, last_name, dept_id <== Row: 1, tom, 1 <== Total: 1 tom Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@69ea3742] Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@69ea3742] Returned connection 1776957250 to pool.
如果打印部门相关信息，例如通用测试的代码（由于实体都重写了toString方法，因此打印employee的时候也打印了department，所以也是使用了部门信息），此时的日志为：
Created connection 1776957250. Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@69ea3742] ==> Preparing: select * from employee where id = ? ==> Parameters: 1(Integer) <== Columns: id, last_name, dept_id <== Row: 1, tom, 1 <== Total: 1 ==> Preparing: select id,dept_name from department where id = ? ==> Parameters: 1(Integer) <== Columns: id, dept_name <== Row: 1, A <== Total: 1 Employee{id=1, lastName=‘tom‘, department=Department{id=1, deptName=‘A‘}} Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@69ea3742] Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@69ea3742] Returned connection 1776957250 to pool.
标签：ref sso org mit action 支持 tin 信息 ltm
原文地址：https://www.cnblogs.com/ye-feng-yu/p/11037555.html
