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
create table t_wife(id int primary key auto_increment,wife_name varchar(),fk_husband_id int);create table t_husband(id int primary key auto_increment,husband_name varchar());insert into t_husband values (null,'hello');insert into t_wife values(null,'kitty',)
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
package com.cy.mybatis.beans;import java.io.Serializable;/*** one to one* @author acer**/public class HusbandBean implements Serializable{private static final long serialVersionUID = L;private Integer id;private String name;private WifeBean wife;public HusbandBean() {super();}public HusbandBean(Integer id, String name, WifeBean wife) {super();this.id = id;this.name = name;this.wife = wife;}public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public WifeBean getWife() {return wife;}public void setWife(WifeBean wife) {this.wife = wife;}@Overridepublic String toString() {return "Husband [id=" + id + ", name=" + name + ", wife=" + wife + "]";}}WifeBean.java
package com.cy.mybatis.beans;import java.io.Serializable;/*** one to one* @author acer**/public class WifeBean implements Serializable{private static final long serialVersionUID = L;private Integer id;private String name;private HusbandBean husband;public WifeBean() {super();}public WifeBean(Integer id, String name, HusbandBean husband) {super();this.id = id;this.name = name;this.husband = husband;}public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public HusbandBean getHusband() {return husband;}public void setHusband(HusbandBean husband) {this.husband = husband;}@Overridepublic String toString() {return "Wife [id=" + id + ", name=" + name + ", husband=" + husband+ "]";}} 3）接下来建立两个接口，HusbandMapper,WifeMapper.
HusbandMapper
package com.cy.mybatis.mapper;import com.cy.mybatis.beans.HusbandBean;public interface HusbandMapper {/*** 根据id查询丈夫信息* @param id* @return* @throws Exception*/public HusbandBean selectHusbandById (int id) throws Exception;/*** 根据id查询丈夫与妻子信息* @param id* @return* @throws Exception*/public HusbandBean selectHusbandAndWife(int id) throws Exception;} 4）定义HusbandMapper.xml文件
<?xml version="." encoding="UTF-"?><!DOCTYPE mapper PUBLIC "-//mybatis.org/DTD Mapper ." "http://mybatis.org/dtd/mybatis--mapper.dtd"><mapper namespace="com.cy.mybatis.mapper.HusbandMapper"><resultMap type="HusbandBean" id="husbandAndWife"><id property="id" column="id" javaType="java.lang.Integer"/><result property="name" column="name" javaType="java.lang.String"/><!-- association 一个复杂的类型关联；许多结果将包成这种类型嵌入结果映射 结果映射自身的关联，或者参考一个column="id" 这里的id指的是在t_wife表来的主键id 这个查询妻子，所以在妻子mapper里有个方法 --><association property="wife" column="id" javaType="WifeBean" select="com.cy.mybatis.mapper.WifeMapper.selectWifeByHusbandId" ></association></resultMap><!-- 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。--><select id="selectHusbandById" resultType="HusbandBean">select * from t_husband where id=#{id}</select> <!-- resultMap 命名引用外部的 resultMap。返回的是一个集合。--><select id="selectHusbandAndWife" resultMap="husbandAndWife">select * from t_husband where id=#{id}</select></mapper> 在WifeMapper.xml里有个方法
<?xml version="." encoding="UTF-"?><!DOCTYPE mapper PUBLIC "-//mybatis.org/DTD Mapper ." "http://mybatis.org/dtd/mybatis--mapper.dtd"><mapper namespace="com.cy.mybatis.mapper.WifeMapper"><select id="selectWifeByHusbandId" resultType="WifeBean">select * from t_wife where fk_husband_id = #{id}</select> </mapper> 5）写个实现
package com.cy.mybatis.service;import org.apache.ibatis.session.SqlSession;import com.cy.mybatis.beans.HusbandBean;import com.cy.mybatis.mapper.HusbandMapper;import com.cy.mybatis.tools.DBTools;public class OneToOneService {public static void main(String[] args) {selectHusbandAndWife();}private static void selectHusbandAndWife() {SqlSession session = DBTools.getSession();HusbandMapper hm = session.getMapper(HusbandMapper.class);try {HusbandBean husband = hm.selectHusbandAndWife();System.out.println(husband);session.commit();} catch (Exception e) {e.printStackTrace();}}} 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
create table t_key(id int primary key auto_increment,key_name varchar(),fk_lock_id int );create table t_lock(id int primary key auto_increment,lock_name varchar());
2.2) 实体类
KeyBean.java
package com.cy.mybatis.beans;import java.io.Serializable;/*** manyTOone* **/public class KeyBean implements Serializable {private static final long serialVersionUID = L;private Integer id;private String key;private LockBean lock;public KeyBean() {super();}public KeyBean(Integer id, String key, LockBean lock) {super();this.id = id;this.key = key;this.lock = lock;}public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getKey() {return key;}public void setKey(String key) {this.key = key;}public LockBean getLock() {return lock;}public void setLock(LockBean lock) {this.lock = lock;}@Overridepublic String toString() {return "KeyBean [id=" + id + ", key=" + key + ", lock=" + lock + "]";}} LockBean.javapackage com.cy.mybatis.beans;import java.io.Serializable;import java.util.List;/*** oneTOmany* **/public class LockBean implements Serializable{private static final long serialVersionUID = L;private Integer id;private String lock;private List<KeyBean> keys;public LockBean() {super();}public LockBean(Integer id, String lock, List<KeyBean> keys) {super();this.id = id;this.lock = lock;this.keys = keys;}public Integer getId() {return id;}public void setId(Integer id) {this.id = id;}public String getLock() {return lock;}public void setLock(String lock) {this.lock = lock;}public List<KeyBean> getKeys() {return keys;}public void setKeys(List<KeyBean> keys) {this.keys = keys;}@Overridepublic String toString() {return "LockBean [id=" + id + ", keys=" + keys + ", lock=" + lock + "]";}} 2.3) 建立接口
KeyMapper.javapackage com.cy.mybatis.mapper;import java.util.List;import org.apache.ibatis.annotations.Param;import com.cy.mybatis.beans.KeyBean;public interface KeyMapper {/*** 批量添加钥匙* @return* 提倡 这样使用 @Param("keys")*/public int batchSaveKeys(@Param("keys")List<KeyBean> keys);} LockMapper.javapackage com.cy.mybatis.mapper;import org.apache.ibatis.annotations.Param;import com.cy.mybatis.beans.LockBean;public interface LockMapper {/*** 添加锁* @param lock* @return*/public int saveLock(@Param("lock")LockBean lock);/*** 根据ID查询锁的资料* @param id* @return*/public LockBean findLockById(int id);/*** 根据ID查询锁与钥匙的资料* onemany* @param id* @return*/public LockBean findLockAndKeys(int id);} 2.4) 建立xml文件
KeyMapper.xml
<?xml version="." encoding="UTF-"?><!DOCTYPE mapper PUBLIC "-//mybatis.org/DTD Mapper ." "http://mybatis.org/dtd/mybatis--mapper.dtd"><mapper namespace="com.cy.mybatis.mapper.KeyMapper"><resultMap id="keyMap" type="KeyBean"><id property="id" column="id" javaType="java.lang.Integer"/><result property="key" column="key_name" javaType="java.lang.String"/></resultMap><!--collection 为用于遍历的元素（必选），支持数组、List、Set --><!-- item 表示集合中每一个元素进行迭代时的别名. --><!--separator表示在每次进行迭代之间以什么符号作为分隔 符. --><insert id="batchSaveKeys">insert into t_key values <foreach collection="keys" item="key" separator=",">(null,#{key.key},#{key.lock.id})</foreach></insert><select id="findKeysByLockId" resultMap="keyMap">select * from t_key where fk_lock_id = #{id}</select></mapper> LockMapper.xml<?xml version="." encoding="UTF-"?><!DOCTYPE mapper PUBLIC "-//mybatis.org/DTD Mapper ." "http://mybatis.org/dtd/mybatis--mapper.dtd"><mapper namespace="com.cy.mybatis.mapper.LockMapper"><!--自定义返回类型 --><resultMap id="lockMap" type="LockBean"><id property="id" column="id" javaType="java.lang.Integer"/><result property="lock" column="lock_name" javaType="java.lang.String"/></resultMap><!--自定义返回类型 --><resultMap id="lockAndKeysMap" type="LockBean"><id property="id" column="id" javaType="java.lang.Integer"/><result property="lock" column="lock_name" javaType="java.lang.String"/><collection property="keys" column="id" select="com.cy.mybatis.mapper.KeyMapper.findKeysByLockId"></collection></resultMap><insert id="saveLock">insert into t_lock values (null,#{lock.lock}) </insert><select id="findLockById" resultMap="lockMap">select * from t_lock where id= #{id}</select><select id="findLockAndKeys" resultMap="lockAndKeysMap">select * from t_lock where id= #{id}</select></mapper> 2.5 ） 实现
package com.cy.mybatis.service;import java.util.ArrayList;import java.util.List;import org.apache.ibatis.session.SqlSession;import com.cy.mybatis.beans.KeyBean;import com.cy.mybatis.beans.LockBean;import com.cy.mybatis.mapper.KeyMapper;import com.cy.mybatis.mapper.LockMapper;import com.cy.mybatis.tools.DBTools;public class OneToManyService {public static void main(String[] args) {// saveLock();// batchSaveKeys();findLockAndKeys();}private static void findLockAndKeys() {SqlSession session = DBTools.getSession();LockMapper lm = session.getMapper(LockMapper.class);LockBean lock = lm.findLockAndKeys();System.out.println(lock);}private static void batchSaveKeys() {SqlSession session = DBTools.getSession();LockMapper lm = session.getMapper(LockMapper.class);KeyMapper km = session.getMapper(KeyMapper.class);LockBean lock = lm.findLockById();List<KeyBean> keys = new ArrayList<KeyBean>();for(int i = ; i < ; i++){KeyBean key = new KeyBean(null, "钥匙"+i, lock);keys.add(key);}km.batchSaveKeys(keys);session.commit();}private static void saveLock() {SqlSession session = DBTools.getSession();LockMapper lm = session.getMapper(LockMapper.class);LockBean lock = new LockBean(null, "锁", null);lm.saveLock(lock);session.commit();}} 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。
package com.cy.mybatis.beans;import java.util.List;/*** 定义一个分页对象* * @author* */public class Pager {private int pageNo;// 当前页码private int pageTotal;// 总页码private int rowsTotal;// 总条数private int pageSize;// 每页显示条数private List<Object> list;// 返回的数据集合public int getPageNo() {return pageNo;}public void setPageNo(int pageNo) {this.pageNo = pageNo;}public int getPageTotal() {return pageTotal;}public void setPageTotal(int pageTotal) {this.pageTotal = pageTotal;}public int getRowsTotal() {return rowsTotal;}public void setRowsTotal(int rowsTotal) {this.rowsTotal = rowsTotal;pageTotal = rowsTotal % pageSize == ? rowsTotal / pageSize : rowsTotal / pageSize + ;}public int getPageSize() {return pageSize;}public void setPageSize(int pageSize) {this.pageSize = pageSize;}public List<?> getList() {return list;}public void setList(List<Object> list) {this.list = list;}@Overridepublic String toString() {return "Pager [pageNo=" + pageNo + ", pageTotal=" + pageTotal+ ", rowsTotal=" + rowsTotal + ", pageSize=" + pageSize+ ", list=" + list + "]";}} UserMapper.java接口。package com.cy.mybatis.mapper;import java.util.List;import java.util.Map;import org.apache.ibatis.annotations.Param;import com.cy.mybatis.beans.UserBean;public interface UserMapper {/*** 新增用* @param user* @return* @throws Exception*/public int insertUser(@Param("user")UserBean user) throws Exception;/*** 修改用* @param user* @param id* @return* @throws Exception*/public int updateUser (@Param("u")UserBean user,@Param("id")int id) throws Exception;/*** 除用* @param id* @return* @throws Exception*/public int deleteUser(int id) throws Exception;/*** 根据id查询用户信息* @param id* @return* @throws Exception*/public UserBean selectUserById(int id) throws Exception;/*** 查询所有的用户信息* @return* @throws Exception*/public List<UserBean> selectAllUser() throws Exception;/*** 批量增加* @param user* @return* @throws Exception*/public int batchInsertUser(@Param("users")List<UserBean> user) throws Exception;/*** 批量删除* @param list* @return* @throws Exception*/public int batchDeleteUser(@Param("list")List<Integer> list) throws Exception;/*** 分页查询数据* @param parma* @return* @throws Exception*/public List<UserBean> pagerUser(Map<String, Object> parmas) throws Exception;/*** * 分页统计数据* @param parma* @return* @throws Exception*/public int countUser(Map<String, Object> parmas) throws Exception;} xml文件<?xml version="." encoding="UTF-"?><!DOCTYPE mapper PUBLIC "-//mybatis.org/DTD Mapper ." "http://mybatis.org/dtd/mybatis--mapper.dtd"><mapper namespace="com.cy.mybatis.mapper.UserMapper"><!-- 自定义返回结果集 --><resultMap id="userMap" type="UserBean"><id property="id" column="id" javaType="java.lang.Integer"></id><result property="username" column="username" javaType="java.lang.String"></result><result property="password" column="password" javaType="java.lang.String"></result><result property="account" column="account" javaType="java.lang.Double"></result></resultMap><!-- 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--> <!-- useGeneratedKeys：（ 仅 对 insert 有 用 ） 这 会 告 诉 MyBatis 使 用 JDBC 的getGeneratedKeys 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。 --> <!--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。 --><!--#{}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 --><insert id="insertUser" useGeneratedKeys="true" keyProperty="user.id">insert into t_user (username,password,account) values (#{user.username},#{user.password},#{user.account})</insert><update id="updateUser">update t_user set username=#{u.username},password=#{u.password},account=#{u.account} where id=#{id}</update><delete id="deleteUser" parameterType="int">delete from t_user where id=#{id} </delete><select id="selectUserById" parameterType="int" resultMap="userMap">select * from t_user where id=#{id}</select><select id="selectAllUser" resultMap="userMap">select * from t_user</select><!-- 批量操作和foreach标签 --><insert id="batchInsertUser" parameterType="java.util.List">insert into t_user values <foreach collection="users" item="users" separator=",">(null,#{users.username},#{users.password},#{users.account})</foreach></insert><delete id="batchDeleteUser">delete from t_user where id in (<foreach collection="list" item="list" separator=",">#{id}</foreach>)</delete><!--collection 为用于遍历的元素（必选），支持数组、List、Set --><!-- item 表示集合中每一个元素进行迭代时的别名. --><!--separator表示在每次进行迭代之间以什么符号作为分隔 符. --><select id="pagerUser" parameterType="java.util.Map" resultMap="userMap">select * from t_user where =<if test="username!=null">and username like '%${username}%'</if>limit ${index},${pageSize} </select><select id="countUser" parameterType="java.util.Map" resultType="int">select count(*) from t_user where = <if test="username != null">and username like '%${username}%' </if></select></mapper> #在生成SQL时，对于字符类型参数，会拼装引号$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package com.cy.mybatis.service;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;import org.apache.ibatis.session.SqlSession;import com.cy.mybatis.beans.UserBean;import com.cy.mybatis.tools.DBTools;import com.cy.mybatis.mapper.UserMapper;public class UserService {/*** @param args*/public static void main(String[] args) {// insertUser();// deleteUser();// updateUser();// selectUserById();// selectAllUser();// batchInsertUser();// batchDeleteUser();// countUser();pagerUser();}private static void countUser() {SqlSession session = DBTools.getSession();UserMapper mapper = session.getMapper(UserMapper.class);Map<String,Object> params = new HashMap<String,Object>();params.put("username", "kitty");int index = ;params.put("index", index);//从第几页开始。mysql是从开始的params.put("pageSize", );//每页显示的数据条数int count;try {count = mapper.countUser(params);System.out.println(count);} catch (Exception e) {e.printStackTrace();}}private static void pagerUser() {SqlSession session = DBTools.getSession();UserMapper mapper = session.getMapper(UserMapper.class);Map<String,Object> params = new HashMap<String,Object>();params.put("username", "kitty");params.put("index", );//从第几页开始。mysql是从开始的params.put("pageSize", );//每页显示的数据条数try {List<UserBean> u = mapper.pagerUser(params);for (UserBean userBean : u) {System.out.println("--------"+userBean);}} catch (Exception e) {e.printStackTrace();}}private static void batchDeleteUser() {SqlSession session = DBTools.getSession();UserMapper mapper = session.getMapper(UserMapper.class);List<Integer> ids = new ArrayList<Integer>();for(int i = ; i < ; i ++){ids.add(i);}try {mapper.batchDeleteUser(ids);session.commit();} catch (Exception e) {e.printStackTrace();}}private static void batchInsertUser() {SqlSession session = DBTools.getSession();UserMapper mapper = session.getMapper(UserMapper.class);List<UserBean> users = new ArrayList<UserBean>();for(int i = ; i < ; i ++){UserBean user = new UserBean("kitty"+i, "", .);users.add(user);}try {mapper.batchInsertUser(users);session.commit();} catch (Exception e) {e.printStackTrace();}}/*** 新增用户*/private static void insertUser() {SqlSession session = DBTools.getSession();UserMapper mapper = session.getMapper(UserMapper.class);UserBean user = new UserBean("懿", "", .);try {mapper.insertUser(user);System.out.println(user.toString());session.commit();} catch (Exception e) {e.printStackTrace();session.rollback();}}/*** 删除用户*/private static void deleteUser(){SqlSession session=DBTools.getSession();UserMapper mapper=session.getMapper(UserMapper.class);try {mapper.deleteUser();session.commit();} catch (Exception e) {e.printStackTrace();session.rollback();}}/*** 修改用户数据*/private static void updateUser(){SqlSession session=DBTools.getSession();UserMapper mapper=session.getMapper(UserMapper.class);UserBean user =new UserBean("小明", "",.);try {mapper.updateUser(user, );session.commit();} catch (Exception e) {e.printStackTrace();session.rollback();}}/*** 根据id查询用户*/private static void selectUserById(){SqlSession session=DBTools.getSession();UserMapper mapper=session.getMapper(UserMapper.class);try {UserBean user= mapper.selectUserById();System.out.println(user.toString());session.commit();} catch (Exception e) {e.printStackTrace();session.rollback();}}/*** 查询所有的用户*/private static void selectAllUser(){SqlSession session=DBTools.getSession();UserMapper mapper=session.getMapper(UserMapper.class);try {List<UserBean> user=mapper.selectAllUser();System.out.println(user.toString());session.commit();} catch (Exception e) {e.printStackTrace();session.rollback();}} } 看一下项目的整体：
每件事都需要坚持！