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; } @Override public 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; } @Override public 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

<" 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> <> <select id="selectHusbandAndWife" resultMap="husbandAndWife"> select * from t_husband where id=#{id} </select> </mapper>

在WifeMapper.xml里有个方法

<" 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; } @Override public String toString() { return "KeyBean [id=" + id + ", key=" + key + ", lock=" + lock + "]"; } } LockBean.java package 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; } @Override public String toString() { return "LockBean [id=" + id + ", keys=" + keys + ", lock=" + lock + "]"; } }

2.3) 建立接口

KeyMapper.java package 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.java package 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

<" 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> <> <> <> <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 <" encoding="UTF-"?> <!DOCTYPE mapper PUBLIC "-//mybatis.org/DTD Mapper ." "http://mybatis.org/dtd/mybatis--mapper.dtd"> <mapper namespace="com.cy.mybatis.mapper.LockMapper"> <> <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> <> <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; } @Override public 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 { /** * 新增用戶 * @param user * @return * @throws Exception */ public int insertUser(@Param("user")UserBean user) throws Exception; /** * 修改用戶 * @param user * @param id * @return * @throws Exception */ public int updateUser (@Param("u")UserBean user,@Param("id")int id) throws Exception; /** * 刪除用戶 * @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 <" encoding="UTF-"?> <!DOCTYPE mapper PUBLIC "-//mybatis.org/DTD Mapper ." "http://mybatis.org/dtd/mybatis--mapper.dtd"> <mapper namespace="com.cy.mybatis.mapper.UserMapper"> <> <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> <> <!-- 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。 --> <> <> <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> <> <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> <> <> <> <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！