Question

I have a table: -\frac{1}{12}x^2+9 and y=6.

The y=9 table contains column Person(int (primary key), varchar, varchar, varchar) - it is varchar which indicates type of person. Person of different types has different skills - so Skill(int (references to person id), varchar, integer) table. No, in my Java classes I have abstract model of Person and concrete kinds, lets call them kind.

Now, during retrieving data by mybatis I need create actual instances of class and return Skill. I have no idea how to reach this effect. Can you help me, please ? Keep in mind that Person will be joined with A,B,C, so different instances in list has different attributes.

Answer 1

让我们阅读MyBatis ducuments，MyBatis3 - Mapper XML Files。对于这种O / R Mapper，您需要创建映射器文件，这些文件指示实际的模型类。之后，您应该编写一些配置来连接表。

<强> DDL

我猜您的表设置如下：

CREATE TABLE `person` (
  `id` INT(10) 
  , `first_name` VARCHAR(18) 
  , `last_name` VARCHAR(18)
  , `kind` VARCHAR(1)
  , `age` INT);

CREATE TABLE `skill` (
  `id` INT(10)
  , `person_id` INT(10)
  , `desc` VARCHAR(200)
);

INSERT INTO `person`(`id`, `first_name`, `last_name`, `kind`, `age`)
VALUES (1, 'John', 'Smith', 'E', 33)
, (2, 'Jane', 'Smith', 'A', 24)
, (3, 'Jonny', 'Smith', 'B', 55)
, (4, 'J', 'J', 'T', 45)
, (5, 'Alan', 'Turing', 'C', 4);

INSERT INTO `skill`(`id`, `person_id`, `desc`)
VALUES (1, 1, 'John Smith is Engineer')
, (2, 2, 'Jane Smith is Artist')
, (3, 3, 'Jonny Smith is Butcher')
, (4, 4, 'J.J is Teacher')
, (5, 5, 'Alan Turing is Computer');

配置完成后，您可以使用密钥连接两个表。这是你的Pokemon列表。

SELECT * FROM `person` p
LEFT JOIN `skill` s
ON s.person_id = p.id;

SQLFiddle链接→SQL Fiddle

我相信您的person_id可以唯一地确定记录。

模型类

人类

// @Data <-- lombok can generate getter/setter easily
public class Person {
    private Integer id;
    private String firstName;
    private String lastName;
    private String kind; // <-- it might be better to use enum
    private Integer age;
    // with getter/setter or annotations
}

技能课

// @Data
public class Skill {
    private Integer id;
    private Integer personId;
    private String desc;
    // with getter/setter or annotations
}

加入PersonSkill类

@Data
public class PersonSkill {
    private Integer id;
    private String firstName;
    private String lastName;
    private String kind;
    private Integer age;
    private Integer skillId;
    private String desc;    
}

映射文件

将结果集保存为模型类的XML配置

<强> PersonSkillMapper.xml

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="jp.gr.java_conf.hangedman.mybatis_join_sample.mappers.PersonSkillMapper">
    <resultMap id="personSkillResultMap" type="PersonSkill">
        <result property="id"        column="id" />
        <result property="firstName" column="first_name" />
        <result property="lastName"  column="last_name" />
        <result property="kind"      column="kind" />
        <result property="age"       column="age" />
        <result property="skillId"   column="skill_id" />
        <result property="desc"      column="desc" />
    </resultMap>
    <select id="selectList" resultMap="personSkillResultMap">
        SELECT
            p.*
            , s.id AS skill_id
            , s.desc AS desc 
        FROM `person` p

        LEFT JOIN `skill` s
        ON s.person_id = p.id
    </select>
</mapper>

生成

public class App { public static void main(String[] args) throws IOException { try (InputStream in = App.class.getResourceAsStream("/mybatis-config.xml")) { SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(in); try (SqlSession session = factory.openSession()) { List<PersonSkill> pskills = session .selectList("jp.gr.java_conf.hangedman.mybatis_join_sample.mappers.PersonSkillMapper.selectList"); for (PersonSkill ps : pskills) { System.out.println(ps.toString()); } } } } }

<强> PS 如果您想创建一些变量属性，可能需要使用Generics。如果你想使用它，请发表评论。

Retrieve from table different types and map it using myBatis

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