Mybatis入门

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本文详细介绍了MyBatis框架的基本原理及使用方法，包括配置文件、SQL映射、CRUD操作、关联查询、模糊查询及多条件查询等关键功能。

一、基本原理

1. 应用程序找Mybatis要数据
2. mybatis从数据库中找来数据
2.1 通过mybatis-config.xml 定位哪个数据库
2.2 通过Category.xml执行对应的select语句
2.3 基于Category.xml把返回的数据库记录封装在Category对象中
2.4 把多个Category对象装在一个Category集合中
3. 返回一个Category集合

//POJO类
public class Category {
	 private int id;
	    private String name;
	    List<Product> products;
	    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 List<Product> getProducts() {
	        return products;
	    }
	    public void setProducts(List<Product> products) {
	        this.products = products;
	    }
	    @Override
	    public String toString() {
	        return "Category [id=" + id + ", name=" + name + "]";
	    }
}

<!-- 定义SQL语句 -->
<?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="pojo">
        <resultMap type="Category" id="categoryBean">
            <id column="cid" property="id" />
            <result column="cname" property="name" />
     
            <!-- 一对多的关系 -->
            <!-- property: 指的是集合属性的值, ofType：指的是集合中元素的类型 -->
            <collection property="products" ofType="Product">
                <id column="pid" property="id" />
                <result column="pname" property="name" />
                <result column="price" property="price" />
            </collection>
        </resultMap>
     
        <!-- 关联查询分类和产品表 -->
        <select id="listCategory1" resultMap="categoryBean">
            select c.*, p.*, c.id 'cid', p.id 'pid', c.name 'cname', p.name 'pname' from category_ c left join product_ p on c.id = p.cid
        </select>   
    
        <select id="listCategory" resultType="Category">
            select * from   category_     
        </select>
        
        <insert id="addCategory" parameterType="Category" >
            insert into category_ ( name ) values (#{name})   
        </insert>
         
        <delete id="deleteCategory" parameterType="Category" >
            delete from category_ where id= #{id}  
        </delete>
         
        <select id="getCategory" parameterType="_int" resultType="Category">
            select * from   category_  where id= #{id}   
        </select>
 
        <update id="updateCategory" parameterType="Category" >
            update category_ set name=#{name} where id=#{id}   
        </update>
        
        <select id="listCategoryByName"  parameterType="string" resultType="Category">
            select * from   category_  where name like concat('%',#{0},'%')
        </select>   
        
        <select id="listCategoryByIdAndName"  parameterType="map" resultType="Category">
            select * from   category_  where id> #{id}  and name like concat('%',#{name},'%')
		</select>
        <select id="listProduct" resultType="Product">
        	select * from product
        </select>
    </mapper>

<!-- MyBatis配置文件 -->
<?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="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="g4885885"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="pojo/Category.xml"/>
    </mappers>
</configuration>

//主程序
import java.io.IOException;
import java.io.InputStream;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

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 pojo.Category;
import 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();
        
        //增
        Category Ca = new Category();
        Ca.setName("新增加的Category");
        session.insert("addCategory",Ca);
        
        //删
        Category Cb = new Category();
        Cb.setId(3);
        session.delete("deleteCategory",Cb);
        
        //查
        Category Cc= session.selectOne("getCategory",2);
        System.out.println("查 "+Cc.getName());
        
        //改（先查后改)
        Category Cd= session.selectOne("getCategory",2);
        Cd.setName("修改了的Category名稱");
        session.update("updateCategory",Cd);
        
        //模糊查询
        List<Category> Ce = session.selectList("listCategoryByName","cat");
        for (Category c : Ce) {
            System.out.println("模糊查询 "+c.getName());
        }
        
        //多条件查询
        Map<String,Object> params = new HashMap<>();
        params.put("id", 1);
        params.put("name", "cat");
         
        List<Category> Cf = session.selectList("listCategoryByIdAndName",params);
        for (Category c : Cf) {
            System.out.println("多条件查询"+c.getName());
        }
        
        //全部查询
        List<Category> cs=session.selectList("listCategory");
        for (Category c : cs) {
            System.out.println("全部查询"+c.getName());
            System.out.println("全部查询"+c.getId());
        }
         
        //一对多两表查询
        List<Category> Cg = session.selectList("listCategory1");
        for (Category c : Cg) {
            System.out.println(c);
            List<Product> ps = c.getProducts();
            for (Product p : ps) {
                System.out.println("\t"+p);
            }
        }
 
        List<Product> cs1=session.selectList("listProduct");
        for (Product c : cs1) {
            System.out.println(c.getName());
            System.out.println(c.getId());
        }
        
    }
}