一、处理属性名与字段名不同问题

1.通过设置查询别名，使类属性名与字段名（数据库内的名）一致

2.设置全局配置，使下划线自动映射为驼峰

<settings><setting name="mapUnderscoreToCamelCase" value="true"/>
</settings>

3.ResultMap

<resultMap id="empResultMap" type="com.mybatis.Bean.Emp"><!--        id,说明主键，property 表示属性名，column 表示字段名--><id property="eid" column="eid" ></id><result property="name" column="name"></result><result property="age" column="age"></result><result property="sex" column="sex"></result><result property="email" column="email"></result><result property="did" column="did"></result>
</resultMap><select id="getEmpt" resultMap="empResultMap">select * from emp
</select>

二、处理多对一映射问题

前提背景

package com.mybatis.Bean;public class Dept {private int did;private String name;public int getDid() {return did;}public void setDid(int did) {this.did = did;}public String getName() {return name;}public void setName(String name) {this.name = name;}@Overridepublic String toString() {return "Dept{" +"did=" + did +", name='" + name + '\'' +'}';}
}

package com.mybatis.Bean;public class Emp {private int eid;private String name;private int age;private char sex;private String email;private  Dept dept;public Dept getDept() {return dept;}public void setDept(Dept dept) {this.dept = dept;}@Overridepublic String toString() {return "Emp{" +"eid=" + eid +", name='" + name + '\'' +", age=" + age +", sex=" + sex +", email='" + email + '\'' +", dept=" + dept +'}';}public int getEid() {return eid;}public void setEid(int eid) {this.eid = eid;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public char getSex() {return sex;}public void setSex(char sex) {this.sex = sex;}public String getEmail() {return email;}public void setEmail(String email) {this.email = email;}}

1.使用级联来实现

<resultMap id="empResultMap" type="com.mybatis.Bean.Emp"><!--        id,说明主键，property 表示属性名，column 表示字段名--><id property="eid" column="eid" ></id><result property="name" column="name"></result><result property="age" column="age"></result><result property="sex" column="sex"></result><result property="email" column="email"></result><result property="dept.did" column="did"></result><result property="dept.name" column="dname"></result>
</resultMap><select id="getEmpt" resultMap="empResultMap">select * from emp left join dept 
</select>

2.association 标签实现

 <resultMap id="empResultMap_" type="com.mybatis.Bean.Emp"><!--        id,说明主键，property 表示属性名，column 表示字段名--><id property="eid" column="eid" ></id><result property="name" column="name"></result><result property="age" column="age"></result><result property="sex" column="sex"></result><result property="email" column="email"></result><association property="dept" javaType="com.mybatis.Bean.Dept"><id property="did" column="did"></id><id property="name" column="name"></id></association></resultMap>

3.分步查询来实现

三、处理一对多问题

背景

package com.mybatis.Bean;import java.util.List;public class Dept {private int did;private String name;private List<Emp> emps;public List<Emp> getEmps() {return emps;}@Overridepublic String toString() {return "Dept{" +"did=" + did +", name='" + name + '\'' +", emps=" + emps +'}';}public void setEmps(List<Emp> emps) {this.emps = emps;}public int getDid() {return did;}public void setDid(int did) {this.did = did;}public String getName() {return name;}public void setName(String name) {this.name = name;}}

1.collection实现

   <resultMap id="xx" type="com.mybatis.Bean.Dept"><id property="did" column="did"></id><result property="name" column="name"></result><!--        collection 处理一对多的映射关系ofType 表示集合中的属性类型
--><collection property="emps" ofType="com.mybatis.Bean.Emp"><id property="eid" column="eid"></id><result property="name" column="name"></result></collection></resultMap><select id="xxx" resultMap="xx"></select>

2.分步查询