Mybatis 多对一_注解

最新推荐文章于 2023-09-09 15:38:14 发布

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本文详细介绍了MyBatis框架的配置过程，包括mybatis-config.xml文件的解析，展示了如何通过配置文件指定数据库连接参数、定义类型别名、设置环境变量以及注册Mapper。同时，深入探讨了Mapper接口与XML映射文件的结合使用，实现了一对多的数据查询，具体演示了从数据库获取产品及其所属分类的过程。

Mybatis-config.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <typeAliases>
        <package name="com.how2java.pojo"/>
    </typeAliases>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/how2java?characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="admin"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper class="com.how2java.mapper.CategoryMapper"/>
        <mapper class="com.how2java.mapper.ProductMapper"/>
    </mappers>
</configuration>

ProductMapper.java

package com.how2java.mapper;
  
import java.util.List;
 
import org.apache.ibatis.annotations.One;
import org.apache.ibatis.annotations.Result;
import org.apache.ibatis.annotations.Results;
import org.apache.ibatis.annotations.Select;
 
import com.how2java.pojo.Product;
  
public interface ProductMapper {
    @Select(" select * from product_ ")
    @Results({ 
        @Result(property="category",column="cid",one=@One(select="com.how2java.mapper.CategoryMapper.get")) 
    })
    public List<Product> list();
}

Product.java

package com.how2java.pojo;

public class Product {
    private int id;
    private String name;
    private float price;
    private Category category;

    public Category getCategory() {
        return category;
    }
    public void setCategory(Category category) {
        this.category = category;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public float getPrice() {
        return price;
    }
    public void setPrice(float price) {
        this.price = price;
    }
    @Override
    public String toString() {
        return "Product [id=" + id + ", name=" + name + ", price=" + price + "]";
    }

}

CategoryMapper.java

package com.how2java.mapper;
  
import org.apache.ibatis.annotations.Select;
 
import com.how2java.pojo.Category;
  
public interface CategoryMapper {
    @Select(" select * from category_ where id = #{id}")
    public Category get(int id);
     
}

Category.java

package com.how2java.pojo;

import java.util.List;

public class Category {
    private int id;
    private String name;
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    @Override
    public String toString() {
        return "Category [id=" + id + ", name=" + name + "]";
    }

}

TestMybatis.java

package com.how2java;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import com.how2java.mapper.ProductMapper;
import com.how2java.pojo.Product;

public class TestMybatis {

    public static void main(String[] args) throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        SqlSession session = sqlSessionFactory.openSession();
        ProductMapper mapper = session.getMapper(ProductMapper.class);

        List<Product> ps= mapper.list();
        for (Product p : ps) {
            System.out.println(p + "\t对应的分类是:\t" + p.getCategory().getName());
        }

        session.commit();
        session.close();

    }
}