Mybatis学习笔记：（二） java中的实体(对象、List、Set)关系怎样与数据库关联映射_mybatis set key

作者：笔触狂放9 | 2024-05-26 07:03:56

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mybatis set key

其实我刚开始学的时候记得就踩过这个坑，总是搞不清楚那个resultMap中的关联层次，以及参数传递的关系，今天研究看了一下其实是很简单只是以前没有太多的实践，所以不明白其中的机制是什么样的。

Association联合select使用值得注意的细节地方：

这是我使用mybatis的Association联合select使用存着问题的地方，


    <association property="module" column="module_id"   select="queryModule">  </association>  
      <select id="queryModule" resultMap="moduleMap" >  
        select * from sys_module where id =#{id}  
    </select>

其实类似： select * from sys_module where id =resultSet.getInt("module_id")；

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 。

下面来个实验：

一、一对一关系

HusbandBean 


package com.cy.mybatis.beans;import java.io.Serializable;/** * one to one * @author acer * */public class HusbandBean implements Serializable{ private static final long serialVersionUID = 1L; 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 = 1L;
    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
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org/DTD Mapper 3.0" "http://mybatis.org/dtd/mybatis-3-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="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org/DTD Mapper 3.0" "http://mybatis.org/dtd/mybatis-3-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(1);
            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。

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）。
 
KeyBean.java
package com.cy.mybatis.beans;
 
import java.io.Serializable;
/**
 * manyTOone
 * 
 *
 */
public class KeyBean implements Serializable {
 
    
    private static final long serialVersionUID = 3712545874604618746L;
 
    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 + "]";
    }
    
}
package com.cy.mybatis.beans;
 
import java.io.Serializable;
import java.util.List;
/**
 * oneTOmany
 * 
 *
 */
public class LockBean implements Serializable{
 
    private static final long serialVersionUID = 7092410462131162665L;
 
    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
     * one2many
     * @param id
     * @return
     */
    public LockBean findLockAndKeys(int id);
    
}


2.4) 建立xml文件
KeyMapper.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org/DTD Mapper 3.0" "http://mybatis.org/dtd/mybatis-3-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="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org/DTD Mapper 3.0" "http://mybatis.org/dtd/mybatis-3-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(1);
        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(1);
        List<KeyBean> keys = new ArrayList<KeyBean>();
        for(int i = 0; i < 5; 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1", null);
        lm.saveLock(lock);
        session.commit();
    }
}

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