MyBatis学习笔记 关联关系

Posted 2020-09-16

今天主要学习的关联关系是一对一关系与一对多关系。

 

一、一对一关系

还是通过例子来解释说明。（一个妻子对应一个丈夫）。

   1)数据库信息

 

 1 create table t_wife(
 2  id int primary key auto_increment,
 3  wife_name varchar(20),
 4  fk_husband_id int
 5 );
 6 
 7 create table t_husband(
 8 id int primary key auto_increment,
 9 husband_name varchar(20)
10 );
11 
12 insert into t_husband values (null,‘hello‘);
13 insert into t_wife values(null,‘kitty‘,1)

 

 2）对应的JavaBean代码

虽然在数据库里只有一方配置的外键，但是这个一对一是双向的关系。

HusbandBean.java

 1 package com.cy.mybatis.beans;
 2 
 3 import java.io.Serializable;
 4 /**
 5  * one to one
 6  * @author acer
 7  *
 8  */
 9 public class HusbandBean implements Serializable{
10 
11     
12     private static final long serialVersionUID = 1L;
13     
14     private Integer id;
15     private String name;
16     private WifeBean wife;
17     public HusbandBean() {
18         super();
19     }
20     public HusbandBean(Integer id, String name, WifeBean wife) {
21         super();
22         this.id = id;
23         this.name = name;
24         this.wife = wife;
25     }
26     public Integer getId() {
27         return id;
28     }
29     public void setId(Integer id) {
30         this.id = id;
31     }
32     public String getName() {
33         return name;
34     }
35     public void setName(String name) {
36         this.name = name;
37     }
38     public WifeBean getWife() {
39         return wife;
40     }
41     public void setWife(WifeBean wife) {
42         this.wife = wife;
43     }
44     @Override
45     public String toString() {
46         return "Husband [id=" + id + ", name=" + name + ", wife=" + wife + "]";
47     }
48     
49     
50 
51 }

WifeBean.java

 View Code

 

 

 3）接下来建立两个接口，HusbandMapper,WifeMapper.

HusbandMapper

 View Code

 

 4）定义HusbandMapper.xml文件

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE mapper PUBLIC "-//mybatis.org/DTD Mapper 3.0" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
 3 <mapper namespace="com.cy.mybatis.mapper.HusbandMapper">
 4 
 5 <resultMap type="HusbandBean" id="husbandAndWife">
 6   <id property="id" column="id" javaType="java.lang.Integer"/>
 7   <result property="name" column="name" javaType="java.lang.String"/>
 8   
 9   <!--  association – 一个复杂的类型关联；许多结果将包成这种类型
10                                                         嵌入结果映射 – 结果映射自身的关联，或者参考一个
11                        column="id" 这里的id指的是在t_wife表来的主键id  
12                       这个查询妻子，所以在妻子mapper里有个方法 -->
13   <association property="wife" column="id" javaType="WifeBean" select="com.cy.mybatis.mapper.WifeMapper.selectWifeByHusbandId" ></association>
14 </resultMap>
15 
16  <!-- resultType 返回类型 从这条语句中返回的期望类型的类的完全限定名或别名
17                                             。-->
18  <select id="selectHusbandById" resultType="HusbandBean">
19    select * from t_husband where id=#{id}
20  </select> 
21 
22   <!-- resultMap  命名引用外部的 resultMap。返回的是一个集合。-->
23  <select id="selectHusbandAndWife" resultMap="husbandAndWife">
24   select * from t_husband where id=#{id}
25  </select>
26 
27 
28 
29 
30 </mapper>

 

    在WifeMapper.xml里有个方法

1 <?xml version="1.0" encoding="UTF-8"?>
2 <!DOCTYPE mapper PUBLIC "-//mybatis.org/DTD Mapper 3.0" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
3 
4 <mapper namespace="com.cy.mybatis.mapper.WifeMapper">
5    <select id="selectWifeByHusbandId" resultType="WifeBean">
6         select * from t_wife where fk_husband_id = #{id}
7 
8     </select>    
9 </mapper>

 

 

 

5）写个实现

 1 package com.cy.mybatis.service;
 2 
 3 import org.apache.ibatis.session.SqlSession;
 4 
 5 import com.cy.mybatis.beans.HusbandBean;
 6 import com.cy.mybatis.mapper.HusbandMapper;
 7 import com.cy.mybatis.tools.DBTools;
 8 
 9 
10 
11 
12 public class OneToOneService {
13     
14     public static void main(String[] args) {
15         selectHusbandAndWife();
16         
17     }
18 
19     
20     private static void selectHusbandAndWife() {
21         SqlSession session = DBTools.getSession();
22         HusbandMapper hm = session.getMapper(HusbandMapper.class);
23         try {
24             HusbandBean    husband = hm.selectHusbandAndWife(1);
25             System.out.println(husband);
26             session.commit();
27         } catch (Exception e) {
28             e.printStackTrace();
29         }
30     }
31 
32 }

 

 注意：那个工具类还是前一章那样写的，就相当与在昨天的基础上建立的。

注意：

 mybatis实际是对XML进行操作，我们所有的方法都直接定义在XML中，写个接口只是为了更好的符合我们3层的思想，如果不写接口，直接通过session也可以直接操作xml中的方法 ，

 XML中只要有方法，就可以使用，而调用的方式就是：namespace+方法名；

 例外使用resultType时，一定要保证，你属性名与字段名相同；

 如果不相同，就使用resultMap 。

二、一对多关系

还是通过例子来解释说明。（一把锁对应多把钥匙）。

 

2.1）数据库信息 这里没有添加数据了，我们用批量添加数据

 1 create table t_key(
 2 id int primary key auto_increment,
 3 key_name varchar(20),
 4 fk_lock_id int 
 5 );
 6 
 7 
 8 create table t_lock(
 9 id int primary key auto_increment,
10 lock_name varchar(20)
11 );

 

 

 

2.2) 实体类

KeyBean.java

 View Code

LockBean.java

 View Code

 

 

 

2.3) 建立接口

KeyMapper.java

 1 package com.cy.mybatis.mapper;
 2 
 3 import java.util.List;
 4 
 5 import org.apache.ibatis.annotations.Param;
 6 
 7 import com.cy.mybatis.beans.KeyBean;
 8 
 9 public interface KeyMapper {
10     /**
11      * 批量添加钥匙
12      * @return
13      * 提倡 这样使用 @Param("keys")
14      */
15     public int batchSaveKeys(@Param("keys")List<KeyBean> keys);
16 }

 

LockMapper.java

 1 package com.cy.mybatis.mapper;
 2 
 3 import org.apache.ibatis.annotations.Param;
 4 
 5 import com.cy.mybatis.beans.LockBean;
 6 
 7 public interface LockMapper {
 8     /**
 9      * 添加锁
10      * @param lock
11      * @return
12      */
13     public int saveLock(@Param("lock")LockBean lock);
14     
15     /**
16      * 根据ID查询锁的资料
17      * @param id
18      * @return
19      */
20     public LockBean findLockById(int id);
21     
22     /**
23      * 根据ID查询锁与钥匙的资料
24      * one2many
25      * @param id
26      * @return
27      */
28     public LockBean findLockAndKeys(int id);
29     
30 }

 

 

2.4) 建立xml文件

KeyMapper.xml

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE mapper PUBLIC "-//mybatis.org/DTD Mapper 3.0" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
 3 <mapper namespace="com.cy.mybatis.mapper.KeyMapper">
 4     
 5     <resultMap id="keyMap" type="KeyBean">
 6         <id property="id" column="id" javaType="java.lang.Integer"/>
 7         <result property="key" column="key_name" javaType="java.lang.String"/>
 8     </resultMap>
 9     
10     
11     <!--collection 为用于遍历的元素（必选），支持数组、List、Set  -->
12     <!-- item 表示集合中每一个元素进行迭代时的别名. -->
13     <!--separator表示在每次进行迭代之间以什么符号作为分隔 符.  -->
14     <insert id="batchSaveKeys">
15         insert into t_key values 
16         <foreach collection="keys" item="key" separator=",">
17             (null,#{key.key},#{key.lock.id})
18         </foreach>
19     </insert>
20     
21     <select id="findKeysByLockId" resultMap="keyMap">
22         select * from t_key where fk_lock_id = #{id}
23     </select>
24 
25 </mapper>

 

LockMapper.xml

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE mapper PUBLIC "-//mybatis.org/DTD Mapper 3.0" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
 3 <mapper namespace="com.cy.mybatis.mapper.LockMapper">
 4     <!--自定义返回类型  -->
 5     <resultMap id="lockMap" type="LockBean">
 6         <id property="id" column="id" javaType="java.lang.Integer"/>
 7         <result property="lock" column="lock_name" javaType="java.lang.String"/>
 8     </resultMap>
 9     
10     <!--自定义返回类型  -->
11     <resultMap id="lockAndKeysMap" type="LockBean">
12         <id property="id" column="id" javaType="java.lang.Integer"/>
13         <result property="lock" column="lock_name" javaType="java.lang.String"/>
14         
15         <collection property="keys" column="id" select="com.cy.mybatis.mapper.KeyMapper.findKeysByLockId"></collection>
16     </resultMap>
17     
18     <insert id="saveLock">
19         insert into t_lock values (null,#{lock.lock})    
20     </insert>
21     
22     <select id="findLockById" resultMap="lockMap">
23         select * from t_lock where id= #{id}
24     </select>
25     
26     <select id="findLockAndKeys" resultMap="lockAndKeysMap">
27         select * from t_lock where id= #{id}
28     </select>
29 
30 </mapper>

2.5 ） 实现

 1 package com.cy.mybatis.service;
 2 
 3 import java.util.ArrayList;
 4 import java.util.List;
 5 
 6 import org.apache.ibatis.session.SqlSession;
 7 
 8 import com.cy.mybatis.beans.KeyBean;
 9 import com.cy.mybatis.beans.LockBean;
10 import com.cy.mybatis.mapper.KeyMapper;
11 import com.cy.mybatis.mapper.LockMapper;
12 import com.cy.mybatis.tools.DBTools;
13 
14 public class OneToManyService {
15     public static void main(String[] args) {
16 //        saveLock();
17 //        batchSaveKeys();
18         findLockAndKeys();
19     }
20 
21     private static void findLockAndKeys() {
22     
23         SqlSession session = DBTools.getSession();
24         LockMapper lm = session.getMapper(LockMapper.class);
25         LockBean lock = lm.findLockAndKeys(1);
26         System.out.println(lock);
27     }
28 
29     private static void batchSaveKeys() {
30         
31         SqlSession session = DBTools.getSession();
32         LockMapper lm = session.getMapper(LockMapper.class);
33         KeyMapper km = session.getMapper(KeyMapper.class);
34         
35         LockBean lock = lm.findLockById(1);
36         List<KeyBean> keys = new ArrayList<KeyBean>();
37         for(int i = 0; i < 5; i++){
38             KeyBean key = new KeyBean(null, "钥匙"+i, lock);
39             keys.add(key);
40         }
41         km.batchSaveKeys(keys);
42         session.commit();
43     }
44 
45     private static void saveLock() {
46         SqlSession session = DBTools.getSession();
47         LockMapper lm = session.getMapper(LockMapper.class);
48         LockBean lock = new LockBean(null, "锁1", null);
49         lm.saveLock(lock);
50         session.commit();
51     }
52 }

 

结果显示：

 

 

 三 、批量操作与分页

 这里就使用前一章的User.就写出主要的代码。

首先定义分页对象。

 1 package com.cy.mybatis.beans;
 2 
 3 import java.util.List;
 4 
 5 
 6 
 7 /**
 8  * 定义一个分页对象
 9  * 
10  * @author
11  * 
12  */
13 public class Pager {
14 
15     private int pageNo;// 当前页码
16     private int pageTotal;// 总页码
17     private int rowsTotal;// 总条数
18     private int pageSize;// 每页显示条数
19      private List<Object> list;// 返回的数据集合
20 
21     public int getPageNo() {
22         return pageNo;
23     }
24 
25     public void setPageNo(int pageNo) {
26         this.pageNo = pageNo;
27     }
28 
29     public int getPageTotal() {
30         return pageTotal;
31     }
32 
33     public void setPageTotal(int pageTotal) {
34         this.pageTotal = pageTotal;
35     }
36 
37     public int getRowsTotal() {
38         return rowsTotal;
39     }
40 
41     public void setRowsTotal(int rowsTotal) {
42         this.rowsTotal = rowsTotal;
43         pageTotal = rowsTotal % pageSize == 0 ? rowsTotal / pageSize : rowsTotal / pageSize + 1;
44     }
45 
46     public int getPageSize() {
47         return pageSize;
48     }
49 
50     public void setPageSize(int pageSize) {
51         this.pageSize = pageSize;
52     }
53 
54     public List<?> getList() {
55         return list;
56     }
57 
58     public void setList(List<Object> list) {
59         this.list = list;
60     }
61 
62 
63     @Override
64     public String toString() {
65         return "Pager [pageNo=" + pageNo + ", pageTotal=" + pageTotal
66                 + ", rowsTotal=" + rowsTotal + ", pageSize=" + pageSize
67                 + ", list=" + list + "]";
68     }
69 
70 }

 

UserMapper.java接口。

 1 package com.cy.mybatis.mapper;
 2 
 3 import java.util.List;
 4 import java.util.Map;
 5 
 6 import org.apache.ibatis.annotations.Param;
 7 
 8 import com.cy.mybatis.beans.UserBean;
 9 
10 public interface UserMapper {
11     /**
12      * 新增用戶
13      * @param user
14      * @return
15      * @throws Exception
16      */
17     public int insertUser(@Param("user")UserBean user) throws Exception;
18     /**
19      * 修改用戶
20      * @param user
21      * @param id
22      * @return
23      * @throws Exception
24      */
25     public int updateUser (@Param("u")UserBean user,@Param("id")int id) throws Exception;
26      /**
27       * 刪除用戶
28       * @param id
29       * @return
30       * @throws Exception
31       */
32     public int deleteUser(int id) throws Exception;
33     /**
34      * 根据id查询用户信息
35      * @param id
36      * @return
37      * @throws Exception
38      */
39     public UserBean selectUserById(int id) throws Exception;
40      /**
41       * 查询所有的用户信息
42       * @return
43       * @throws Exception
44       */
45     public List<UserBean> selectAllUser() throws Exception;
46     
47     
48     /**
49      * 批量增加
50      * @param user
51      * @return
52      * @throws Exception
53      */
54    public int batchInsertUser(@Param("users")List<UserBean> user) throws Exception;
55    
56    /**
57     * 批量删除
58     * @param list
59     * @return
60     * @throws Exception
61     */
62    public int batchDeleteUser(@Param("list")List<Integer> list) throws Exception;
63    
64    
65    /**
66     * 分页查询数据
67     * @param parma
68     * @return
69     * @throws Exception
70     */
71    public List<UserBean> pagerUser(Map<String, Object> parmas) throws Exception;
72    
73    /**
74     * 
75     * 分页统计数据
76     * @param parma
77     * @return
78     * @throws Exception
79     */
80     public int countUser(Map<String, Object> parmas) throws Exception;
81     
82  
83     
84 }

 

xml文件

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE mapper PUBLIC "-//mybatis.org/DTD Mapper 3.0" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
 3 <mapper namespace="com.cy.mybatis.mapper.UserMapper">
 4 <!-- 自定义返回结果集 -->
 5    <resultMap id="userMap" type="UserBean">
 6         <id property="id" column="id" javaType="java.lang.Integer"></id>
 7         <result property="username" column="username" javaType="java.lang.String"></result>
 8         <result property="password" column="password" javaType="java.lang.String"></result>
 9         <result property="account" column="account" javaType="java.lang.Double"></result>
10     </resultMap>
11 <!-- 在各种标签中的id属性必须和接口中的方法名相同 ， id属性值必须是唯一的，不能够重复使用。parameterType属性指明查询时使用的参数类型，resultType属性指明查询返回的结果集类型-->    
12 <!-- useGeneratedKeys：（ 仅 对 insert 有 用 ） 这 会 告 诉 MyBatis 使 用 JDBC 的getGeneratedKeys 
13             方法来取出由数据（比如：像 mysql 和 SQLServer 这样的数据库管理系统的自动递增字段）内部生成的主键。默认值： false。 -->    
14 <!--keyProperty： （仅对 insert有用）标记一个属性， MyBatis 会通过 getGeneratedKeys或者通过 insert 语句的 selectKey 子元素设置它的值。默认：不设置。 -->
15 <!--#{}中的内容，为占位符，当参数为某个JavaBean时，表示放置该Bean对象的属性值  -->
16 
17 
18     <insert id="insertUser" useGeneratedKeys="true" keyProperty="user.id">
19         insert into t_user (username,password,account) values (#{user.username},#{user.password},#{user.account})
20     </insert>
21     
22     <update id="updateUser">
23       update t_user set username=#{u.username},password=#{u.password},account=#{u.account} where id=#{id}
24     </update>
25     
26     <delete id="deleteUser" parameterType="int">
27      delete from t_user where id=#{id}  
28     </delete>
29     
30     <select id="selectUserById" parameterType="int" resultMap="userMap">
31      select * from t_user where id=#{id}
32     </select>
33     
34     <select id="selectAllUser" resultMap="userMap">
35      select * from t_user
36     </select>
37     
38     
39     
40     
41     <!-- 批量操作和foreach标签 -->
42     
43     <insert id="batchInsertUser" parameterType="java.util.List">
44        insert into t_user values 
45         <foreach collection="users" item="users" separator=",">
46          (null,#{users.username},#{users.password},#{users.account})
47         </foreach>
48     </insert>
49     
50     
51     <delete id="batchDeleteUser">
52        delete from t_user where id in (
53          <foreach collection="list" item="list" separator=",">
54           #{id}
55          </foreach>
56        )
57     </delete>
58     
59     <!--collection 为用于遍历的元素（必选），支持数组、List、Set  -->
60     <!-- item 表示集合中每一个元素进行迭代时的别名. -->
61     <!--separator表示在每次进行迭代之间以什么符号作为分隔 符.  -->
62     
63     
64     <select id="pagerUser" parameterType="java.util.Map" resultMap="userMap">
65       select * from t_user where 1=1
66 
67       <if test="username!=null">
68        and username like ‘%${username}%‘
69       </if>
70        limit ${index},${pageSize} 
71     </select>
72     
73     <select id="countUser" parameterType="java.util.Map" resultType="int">
74         select count(*) from t_user where 1=1 
75         <if test="username != null">
76             and username like ‘%${username}%‘    
77         </if>
78     </select>
79     
80     
81 </mapper>    

 

#在生成SQL时，对于字符类型参数，会拼装引号
$在生成SQL时，不会拼装引号，可用于order by之类的参数拼装

 测试类

  1 package com.cy.mybatis.service;
  2 
  3 import java.util.ArrayList;
  4 import java.util.HashMap;
  5 import java.util.List;
  6 import java.util.Map;
  7 
  8 import org.apache.ibatis.session.SqlSession;
  9 
 10 import com.cy.mybatis.beans.UserBean;
 11 import com.cy.mybatis.tools.DBTools;
 12 import com.cy.mybatis.mapper.UserMapper;
 13 
 14 public class UserService {
 15 
 16     /**
 17      * @param args
 18      */
 19     public static void main(String[] args) {
 20 //        insertUser();
 21 //        deleteUser();
 22 //        updateUser();
 23 //        selectUserById();
 24 //        selectAllUser();
 25         
 26 //        batchInsertUser();
 27 //        batchDeleteUser();
 28 //        countUser();
 29         pagerUser();
 30     }
 31 
 32     
 33     private static void countUser() {
 34         SqlSession session = DBTools.getSession();
 35         UserMapper mapper = session.getMapper(UserMapper.class);
 36         Map<String,Object> params = new HashMap<String,Object>();
 37         params.put("username", "kitty");
 38         int index = 0;
 39         params.put("index", index);//从第几页开始。mysql是从0开始的
 40         params.put("pageSize", 5);//每页显示的数据条数
 41         int count;
 42         try {
 43             count = mapper.countUser(params);
 44             System.out.println(count);
 45         } catch (Exception e) {
 46             e.printStackTrace();
 47         }
 48         
 49     }
 50 
 51 
 52     private static void pagerUser() {
 53         SqlSession session = DBTools.getSession();
 54         UserMapper mapper = session.getMapper(UserMapper.class);
 55         Map<String,Object> params = new HashMap<String,Object>();
 56         params.put("username", "kitty");
 57         params.put("index", 0);//从第几页开始。mysql是从0开始的
 58         params.put("pageSize", 5);//每页显示的数据条数
 59         try {
 60              List<UserBean> u = mapper.pagerUser(params);
 61             for (UserBean userBean : u) {
 62                 System.out.println("--------"+userBean);
 63             }
 64         } catch (Exception e) {
 65             e.printStackTrace();
 66         }
 67         
 68     }
 69 
 70 
 71     private static void batchDeleteUser() {
 72         SqlSession session = DBTools.getSession();
 73         UserMapper mapper = session.getMapper(UserMapper.class);
 74         List<Integer> ids = new ArrayList<Integer>();
 75         for(int i = 4; i < 10; i ++){
 76             ids.add(i);
 77         }
 78         try {
 79             mapper.batchDeleteUser(ids);
 80             session.commit();
 81         } catch (Exception e) {
 82             e.printStackTrace();
 83         }
 84         
 85     }
 86 
 87 
 88     private static void batchInsertUser() {
 89         SqlSession session = DBTools.getSession();
 90         UserMapper mapper = session.getMapper(UserMapper.class);
 91         
 92         List<UserBean> users = new ArrayList<UserBean>();
 93         for(int i = 0; i < 10; i ++){
 94             UserBean user = new UserBean("kitty"+i, "123456", 6000.0);
 95             users.add(user);
 96         }
 97         try {
 98             mapper.batchInsertUser(users);
 99             session.commit();
100         } catch (Exception e) {
101             e.printStackTrace();
102         }
103     }
104 
105 
106     /**
107      * 新增用户
108      */
109     private static void insertUser() {
110         SqlSession session = DBTools.getSession();
111         UserMapper mapper = session.getMapper(UserMapper.class);
112         UserBean user = new UserBean("懿", "1314520", 7000.0);
113         try {
114             mapper.insertUser(user);
115             System.out.println(user.toString());
116              session.commit();
117         } catch (Exception e) {
118             e.printStackTrace();
119             session.rollback();
120         }
121     }
122     
123     
124     /**
125      * 删除用户
126      */
127     private static void deleteUser(){
128         SqlSession session=DBTools.getSession();
129         UserMapper mapper=session.getMapper(UserMapper.class);
130         try {
131             mapper.deleteUser(1);
132             session.commit();
133         } catch (Exception e) {
134             e.printStackTrace();
135             session.rollback();
136         }
137     }
138     
139     /**
140      * 修改用户数据
141      */
142     private static void updateUser(){
143         SqlSession session=DBTools.getSession();
144         UserMapper mapper=session.getMapper(UserMapper.class);
145         UserBean user =new UserBean("小明", "111",6000.0);
146         try {
147             mapper.updateUser(user, 3);
148             session.commit();
149         } catch (Exception e) {
150             e.printStackTrace();
151             session.rollback();
152         }
153     }
154     
155     /**
156      * 根据id查询用户
157      */
158     private static void selectUserById(){
159         SqlSession session=DBTools.getSession();
160         UserMapper mapper=session.getMapper(UserMapper.class);
161         try {
162         UserBean user=    mapper.selectUserById(2);
163         System.out.println(user.toString());
164             
165             session.commit();
166         } catch (Exception e) {
167             e.printStackTrace();
168             session.rollback();
169         }
170     }
171     
172     /**
173      * 查询所有的用户
174      */
175     private static void selectAllUser(){
176         SqlSession session=DBTools.getSession();
177         UserMapper mapper=session.getMapper(UserMapper.class);
178         try {
179         List<UserBean> user=mapper.selectAllUser();
180         System.out.println(user.toString());
181         session.commit();
182         } catch (Exception e) {
183             e.printStackTrace();
184             session.rollback();
185         }
186     }    
187 
188 }

 

 

 

 

 看一下项目的整体：