mybatis關聯查詢之一對多，多對一，以及多對多
阿新 • • 發佈：2019-03-21
idt 兩個 讀取 arrays ebe bubuko print 過濾 權限表 
一、使用IDEA新建maven工程
二、引入mybatis以及相關的jar
<!--版本僅供參考-->
<dependencies> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.12</version> </dependency> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis</artifactId> <version>3.4.5</version> </dependency> <dependency> <groupId>log4j</groupId> <artifactId>log4j</artifactId> <version>1.2.17</version> </dependency> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>5.1.44</version> </dependency> </dependencies>
三、建表
權限管理需求的介紹，一個用戶擁有若幹角色，一個角色擁有若幹權限，權限就是對某個資源的增刪改查，這樣就構成了用戶-角色-權限之間的模型，在這種關系中，用戶與角色，角色與權限之間一般是多對多的關系
建表sql：
create table sys_user( id int not null auto_increment comment ‘用戶ID‘, user_name varchar(32) comment ‘用戶名‘, password varchar(50) comment ‘用戶密碼‘, usr_info varchar(50) comment ‘用戶簡介‘, head_img blob comment ‘頭像‘, create_time datetime comment ‘創建時間‘, primary key(id) ); alter table sys_user comment ‘用戶表‘; create table sys_role( id int not null auto_increment comment ‘角色ID‘, role_name varchar(50) comment ‘角色名稱‘, enabled int comment ‘有效標誌‘, create_by bigint comment‘創建人‘, create_time datetime comment ‘創建時間‘, primary key(id) ); alter table sys_role comment ‘角色表‘; create table sys_privilege( id int not null auto_increment comment ‘權限ID‘, privilege_name varchar(50) comment ‘權限名稱‘, privilege_url varchar(50) comment ‘權限URL‘, primary key(id) ); alter table sys_privilege comment ‘權限表‘; create table sys_user_role( user_id bigint not null comment ‘用戶ID‘, role_id bigint not null comment ‘角色ID‘ ); alter table sys_user comment ‘用戶角色‘; create table sys_role_privilege( role_id bigint not null comment ‘角色ID‘, privilege_id bigint not null comment ‘權限ID‘ ); alter table sys_role_privilege comment ‘角色權限表‘;
給表添加外鍵
-- 給用戶角色表的user_id添加外鍵 alter table sys_user_role add constraint fk_uru foreign key(user_id) references sys_user(id); -- 給用戶角色表的role_id 添加外鍵 alter table sys_user_role add constraint fk_sysrur foreign key(role_id) references sys_role(id); -- 給角色權限表的role_id添加外鍵 alter table sys_role_privilege add constraint fk_sysrpp foreign key(privilege_id) references sys_privilege(id); -- 給角權限的privilege_id 添加外鍵 alter table sys_role_privilege add constraint fk_sysrpr foreign key(role_id) references sys_role(role_id);
插入數據
insert into sys_user(user_name,password,user_info,head_img,create_time )values(‘Jordan‘,‘123‘,‘管理員‘,null,‘2018-1-22 12:02:01‘), (‘Alice‘,‘456‘,‘測試人員‘,null,‘2018-1-22 12:02:01‘), (‘Alex‘,‘789‘,‘開發人員‘,null,‘2018-1-22 12:02:01‘), (‘James‘,‘012‘,‘運維人員‘,null,‘2018-1-22 12:02:01‘) insert into sys_user_role(role_name,enabled,create_by,create_time) values(‘管理員‘,1,‘1‘,‘2018-01-02‘),values(‘普通用戶‘,1,‘1‘,‘2018-01-02‘); insert into sys_privilege(privilege_name,privilege_url) values(‘用戶管理‘,‘/users‘),(‘角色管理‘,‘/roles‘),(‘系統維護‘,‘/system‘),(‘日誌管理‘,‘/logs‘); insert into sys_user_role values(1,1),(2,2),(3,2),(4,2); insert into sys_role_privilege values(1,1),(2,3),(2,4);
四、使用逆向工程生成entity以及mapper接口和mapper文件
①：創建mybatis-config.xml文件
<?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"/> </settings> <typeAliases> <package name="com.jordan.mybatis.entity"></package> </typeAliases> <environments default="defaultEnv"> <environment id="defaultEnv"> <transactionManager type="JDBC"></transactionManager> <dataSource type="POOLED"> <property name="username" value="root"></property> <property name="password" value="123456"></property> <property name="url" value="jdbc:mysql://localhost:3306/mybatis"></property> <property name="driver" value="com.mysql.jdbc.Driver"></property> </dataSource> </environment> </environments> <mappers> <package name="com.jordan.mybatis.mapper"></package> </mappers> </configuration>
②：SysUser.java
package com.jordan.mybatis.entity; import java.util.Arrays; import java.util.Date; import java.util.List; public class SysUser { private Long id; private String userName; private String password; private Date createTime; private String userInfo; private byte[] headImg; private SysRole sysRole; private List<SysRole> sysRoleList; public List<SysRole> getSysRoleList() { return sysRoleList; } public void setSysRoleList(List<SysRole> sysRoleList) { this.sysRoleList = sysRoleList; } public SysRole getSysRole() { return sysRole; } public void setSysRole(SysRole sysRole) { this.sysRole = sysRole; } public Long getId() { return id; } public void setId(Long id) { this.id = id; } public String getUserName() { return userName; } public void setUserName(String userName) { this.userName = userName == null ? null : userName.trim(); } public String getPassword() { return password; } public void setPassword(String password) { this.password = password == null ? null : password.trim(); } public Date getCreateTime() { return createTime; } public void setCreateTime(Date createTime) { this.createTime = createTime; } public String getUserInfo() { return userInfo; } public void setUserInfo(String userInfo) { this.userInfo = userInfo == null ? null : userInfo.trim(); } public byte[] getHeadImg() { return headImg; } public void setHeadImg(byte[] headImg) { this.headImg = headImg; } @Override public String toString() { return "SysUser{" + "id=" + id + ", userName=‘" + userName + ‘\‘‘ + ", password=‘" + password + ‘\‘‘ + ", createTime=" + createTime + ", userInfo=‘" + userInfo + ‘\‘‘ + ", headImg=" + Arrays.toString(headImg) + ", sysRole=" + sysRole + ", sysRoleList=" + sysRoleList + ‘}‘; } }View Code
③：SysRole.java
package com.jordan.mybatis.entity; import java.util.Arrays; import java.util.Date; import java.util.List; public class SysUser { private Long id; private String userName; private String password; private Date createTime; private String userInfo; private byte[] headImg; private SysRole sysRole; private List<SysRole> sysRoleList; public List<SysRole> getSysRoleList() { return sysRoleList; } public void setSysRoleList(List<SysRole> sysRoleList) { this.sysRoleList = sysRoleList; } public SysRole getSysRole() { return sysRole; } public void setSysRole(SysRole sysRole) { this.sysRole = sysRole; } public Long getId() { return id; } public void setId(Long id) { this.id = id; } public String getUserName() { return userName; } public void setUserName(String userName) { this.userName = userName == null ? null : userName.trim(); } public String getPassword() { return password; } public void setPassword(String password) { this.password = password == null ? null : password.trim(); } public Date getCreateTime() { return createTime; } public void setCreateTime(Date createTime) { this.createTime = createTime; } public String getUserInfo() { return userInfo; } public void setUserInfo(String userInfo) { this.userInfo = userInfo == null ? null : userInfo.trim(); } public byte[] getHeadImg() { return headImg; } public void setHeadImg(byte[] headImg) { this.headImg = headImg; } @Override public String toString() { return "SysUser{" + "id=" + id + ", userName=‘" + userName + ‘\‘‘ + ", password=‘" + password + ‘\‘‘ + ", createTime=" + createTime + ", userInfo=‘" + userInfo + ‘\‘‘ + ", headImg=" + Arrays.toString(headImg) + ", sysRole=" + sysRole + ", sysRoleList=" + sysRoleList + ‘}‘; } }View Code
④：SysPrivilege.java
package com.jordan.mybatis.entity; public class SysPrivilege { private Long id; private String privilegeName; private String privilegeUrl; public Long getId() { return id; } public void setId(Long id) { this.id = id; } public String getPrivilegeName() { return privilegeName; } public void setPrivilegeName(String privilegeName) { this.privilegeName = privilegeName == null ? null : privilegeName.trim(); } public String getPrivilegeUrl() { return privilegeUrl; } public void setPrivilegeUrl(String privilegeUrl) { this.privilegeUrl = privilegeUrl == null ? null : privilegeUrl.trim(); } @Override public String toString() { return "SysPrivilege{" + "id=" + id + ", privilegeName=‘" + privilegeName + ‘\‘‘ + ", privilegeUrl=‘" + privilegeUrl + ‘\‘‘ + ‘}‘; } }View Code
⑤:SysUserMapper
public interface SysUserMapper { public List<SysUser> getUserRolePrivilege(); }
⑥：SysUserMapper.xml
<?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.jordan.mybatis.mapper.SysUserMapper"> <resultMap id="getUserRolePrivilege" type="SysUser"> <id property="id" column="id"></id> <result property="userName" column="user_name"></result> <result property="password" column="password"></result> <result property="userInfo" column="user_info"></result> <result property="createTime" column="create_time"></result> <collection property="sysRoleList" ofType="SysRole"> <id property="id" column="id"></id> <result property="roleName" column="role_name"></result> <result property="createTime" column="create_time"></result> <collection property="sysPrivilegeList" ofType="SysPrivilege"> <id property="id" column="id"></id> <result property="privilegeName" column="privilege_name"></result> <result property="privilegeUrl" column="privilege_url"></result> </collection> </collection> </resultMap> <select id="getUserRolePrivilege" resultMap="getUserRolePrivilege"> select a.id,a.user_name,a.password,a.user_info,b.role_name,b.create_time,c.privilege_name,c.privilege_url from sys_user a,sys_role b, sys_privilege c,sys_user_role d,sys_role_privilege e where a.id = d.user_id and b.id = d.role_id and e.role_id=b.id and e.privilege_id=c.id </select> </mapper>
五、在mybatis-config.xml中添加mapper接口以及mapper文件
<mappers>
<package name="com.jordan.mybatis.mapper"></package>
</mappers>
六、創建測試類Test.java
import com.jordan.mybatis.mapper.SysUserMapper; import org.apache.ibatis.io.Resources; import org.apache.ibatis.session.SqlSession; import org.apache.ibatis.session.SqlSessionFactory; import org.apache.ibatis.session.SqlSessionFactoryBuilder; import org.junit.Before; import java.io.IOException; import java.io.InputStream; import java.io.Reader; /** * @author Jordan * @create * @DESCRIPTION */ public class Test { private SqlSessionFactory sqlSessionFactory; @Before public void init() throws IOException{ //1:讀取mybatis的主配置文件 String configFile = "mybatis-config.xml"; InputStream inputStream = Resources.getResourceAsStream(configFile); //2:通過sqlSessionFactoryBuilder創建一個sqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); } @org.junit.Test public void testGetUserRolePrivilege(){ SqlSession sqlSession=sqlSessionFactory.openSession(); SysUserMapper sysUserMapper=sqlSession.getMapper(SysUserMapper.class); System.out.println(sysUserMapper.getUserRolePrivilege().size()); //4 查詢結果與數據庫查詢結果不匹配，發生數據覆蓋問題，解決辦法參考註意事項②
} }
七、註意事項：
①：idea找不到mapper文件的原因：IDEA不會編譯src的java目錄下的xml文件。所以添加如下代碼
<resources>
<!-- resources文件 -->
<resource>
<directory>src/main/resources</directory>
<!-- 是否被過濾,如果被過濾則無法使用 -->
<filtering>false</filtering>
</resource>
<!-- java文件夾 -->
<resource>
<directory>src/main/java</directory>
<!-- 引入映射文件等 -->
<includes>
<include>**/*.xml</include>
<include>**/*.properties</include>
</includes>
</resource>
<resource>
<directory>src/main/webapp</directory>
<includes>
<include>**/*.*</include>
</includes>
</resource>
</resources>
②：mybatis在映射依賴的過程中，如果兩個表中的主鍵是一樣的會發生數據覆蓋問題。
解決辦法：
解決方式一：修改數據庫表中的主鍵（這種方法比較麻煩）；
解決方式二：在查詢語句中修改一個表的主鍵使其不一致即可；
上述代碼測試結果中與數據庫中的查詢記錄不匹配
數據庫查詢結果為8條記錄，但是mybatis查詢只有4條數據，發生數據覆蓋的問題；
修改SysUserMapper.xml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.jordan.mybatis.mapper.SysUserMapper"> <resultMap id="getUserRolePrivilege" type="SysUser"> <id property="id" column="aid"></id> <result property="userName" column="user_name"></result> <result property="password" column="password"></result> <result property="userInfo" column="user_info"></result> <result property="createTime" column="create_time"></result> <collection property="sysRoleList" ofType="SysRole"> <id property="id" column="bid"></id> <result property="roleName" column="role_name"></result> <result property="createTime" column="create_time"></result> <collection property="sysPrivilegeList" ofType="SysPrivilege"> <id property="id" column="cid"></id> <result property="privilegeName" column="privilege_name"></result> <result property="privilegeUrl" column="privilege_url"></result> </collection> </collection> </resultMap> <select id="getUserRolePrivilege" resultMap="getUserRolePrivilege"> select a.id,a.user_name,a.password,a.user_info,b.role_name,b.create_time,c.privilege_name,c.privilege_url from sys_user a,sys_role b, sys_privilege c,sys_user_role d,sys_role_privilege e where a.id = d.user_id and b.id = d.role_id and e.role_id=b.id and e.privilege_id=c.id </select> </mapper>
mybatis關聯查詢之一對多，多對一，以及多對多