Mybatis之一对一关联关系

以你之姓@ 2022-06-09 14:15 241阅读 0赞

今天分享的是一对一关联关系查询。

我们先设计数据库，由于为了方便后面的一对多关系，这里假设作者和书是一对一关联关系。

Book表:

![64155588.jpg][]

Author表:

![94855288.jpg][]

再来创建实体类：

public class Author {
        private int ID;
        private String AuthorName;  
    
        public int getID() {
            return ID;
        }
    
        public void setID(int iD) {
            ID = iD;
        }
    
        public String getName() {
            return AuthorName;
        }
    
        public void setName(String name) {
            AuthorName = name;
        }
    
        public Author(int iD, String name) {
            super();
            ID = iD;
            AuthorName = name;
        }
    
        public Author() {
            // TODO Auto-generated constructor stub
        }
    }
    
    =========================================================
    
      public class Book {
        private int ID;
        private String Name;
        private Author author;  
    
        public Author getAuthor() {
            return author;
        }
    
        public void setAuthor(Author author) {
            this.author = author;
        }
    
        public int getID() {
            return ID;
        }
    
        public void setID(int iD) {
            ID = iD;
        }
    
        public String getName() {
            return Name;
        }
    
        public void setName(String name) {
            Name = name;
        }
    
        public Book(int iD, String name) {
            super();
            ID = iD;
            Name = name;
        }
    
        public Book() {
        }
    }

实体类创建后配置xml文件

Author.xml:

由于查询都在Book.xml里面配置了，所以Author.xml就不用配置了。

Book.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="Book">
        
        <select id="queryBookName" parameterType="int" resultMap="getBookMap">
            select a.*,b.*
            from Book b,Author a
            where a.ID=b.authorID AND a.ID=#{ID}
        </select>
    
        <resultMap type="com.entity.Book" id="getBookMap">
            <id column="ID" property="ID" />
            <result column="Name" property="Name"/>
            <association property="author" javaType="com.entity.Author">
                <id column="ID" property="ID"/>
                <result column="AuthorName" property="AuthorName"/>
            </association>
        </resultMap>
    
    
        
        <select id="queryBookName2" parameterType="int" resultMap="getBookMap2">
            select b.ID,b.Name,b.authorID from Book b where b.ID=#{ID}  
        </select>
    
        
        <select id="getAuthor" parameterType="int" resultType="com.entity.Author">
            select a.ID ,a.AuthorName from Author a where a.ID=#{authorID} 
        </select>
    
        <resultMap type="com.entity.Book" id="getBookMap2">
            <id column="ID" property="ID" />
            <result column="Name" property="Name"/>
            <association property="author" select="getAuthor" column="authorID">
            </association>
        </resultMap>
    
    </mapper>

记得要将这两个xml文件放入configuration文件中。

最后测试代码：

public class AssociationTest {
        public static void main(String[] args) {
            SqlSession session = null;
            try {
                InputStream inputStream = Resources.getResourceAsStream("configure/Configuration.xml");
                session = new SqlSessionFactoryBuilder().build(inputStream).openSession();
                Book book = session.selectOne("queryBookName", 1);
                System.out.println(book.getAuthor().getID()+" "+book.getAuthor().getName());
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } finally {
                if (session!=null) {
                    session.close();
                }
            }
        }
    }

以上就完成了一对一关联关系。

[64155588.jpg]: http://or0um8wrx.bkt.clouddn.com/17-9-7/64155588.jpg
[94855288.jpg]: http://or0um8wrx.bkt.clouddn.com/17-9-7/94855288.jpg