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关于后端:Mybatis系列教材-二十-相关概念-分页

jiezi

步骤 1: 先运行，看到成果，再学习
步骤 2: 模拟和排错
步骤 3: 减少 100 条 catgory 数据
步骤 4: 批改 Category.xml
步骤 5: 测试
步骤 6: 注解形式

步骤 1 : 先运行，看到成果，再学习

老规矩，先下载下载区 (点击进入) 的可运行我的项目，配置运行起来，确认可用之后，再学习做了哪些步骤以达到这样的成果。

步骤 2 : 模拟和排错

在确保可运行我的项目可能正确无误地运行之后，再严格照着教程的步骤，对代码模拟一遍。
模拟过程不免代码有出入，导致无奈失去冀望的运行后果，此时此刻通过比拟 正确答案 (可运行我的项目) 和本人的代码，来定位问题所在。
采纳这种形式，学习有成果，排错有效率，能够较为显著地晋升学习速度，跨过学习路上的各个槛。

举荐应用 diffmerge 软件，进行文件夹比拟。把你本人做的我的项目文件夹，和我的可运行我的项目文件夹进行比拟。
这个软件很牛逼的，能够晓得文件夹里哪两个文件不对，并且很显著地标记进去
这里提供了绿色装置和应用教程：diffmerge 下载和应用教程

步骤 3 : 减少 100 条 catgory 数据

为了察看分页查问的成果，把分类表里的数据都删除掉，而后新增 100 个数据

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.pojo.Category;
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();
        List<Category> cs = session.selectList("listCategory");
        for (Category c : cs) {session.delete("deleteCategory", c);
        }
        for (int i = 0; i < 100; i++) {Category c = new Category();
            c.setName("category name" + i);
            session.insert("addCategory", c);
        }
        List<Category> cs2 = session.selectList("listCategory");
        for (Category c : cs2) {System.out.println(c.getName());
        }
        session.commit();
        session.close();}
}

步骤 4 : 批改 Category.xml

新增 limit

<?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="com.how2java.pojo">
    <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="listCategory" resultType="Category">
        select * from   category_
        <if test="start!=null and count!=null">
            limit #{start},#{count}
        </if>
    </select>
</mapper>

步骤 5 : 测试

用注解形式再做一遍
注： start 是指从第 0 个开始，如果是第二页，那么就是第 5 个开始。
注： count 参数是指每页有 5 条数据

  • CategoryMapper.java
  • TestMybatis.java
package com.how2java.mapper;

import java.util.List;
import org.apache.ibatis.annotations.Many;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Result;
import org.apache.ibatis.annotations.Results;
import org.apache.ibatis.annotations.Select;
import com.how2java.pojo.Category;
public interface CategoryMapper {public List<Category> list();
    public List<Category> listByPage(@Param("start") int start, @Param("count")int count);
}

package com.how2java;
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 com.how2java.mapper.CategoryMapper;
import com.how2java.pojo.Category;
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();
//        xmlWay(session);   
        annotationWay(session);
        session.commit();
        session.close();}
    private static void xmlWay(SqlSession session) {Map<String,Object> params = new HashMap<>();
        params.put("start", 0);
        params.put("count", 5);
        List<Category>  cs =session.selectList("listCategory", params);
        for (Category c : cs) {System.out.println(c);
        }
    }
    private static void annotationWay(SqlSession session) {CategoryMapper mapper = session.getMapper(CategoryMapper.class);

        List<Category>  cs =mapper.listByPage(0, 5);
        for (Category c : cs) {System.out.println(c);
        }
    }
}

步骤 6 : 注解形式

  • CategoryMapper.java
  • TestMybatis.java
package com.how2java.mapper;

import java.util.List;

import org.apache.ibatis.annotations.Many;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Result;
import org.apache.ibatis.annotations.Results;
import org.apache.ibatis.annotations.Select;
import com.how2java.pojo.Category;
public interface CategoryMapper {@Select("select * from category_")
    @Results({@Result(property = "products", javaType = List.class, column = "id",
            many = @Many(select = "com.how2java.mapper.ProductMapper.listByCategory"))})
    public List<Category> list();
    @Select("select * from category_ limit #{start},#{count}")
    public List<Category> listByPage(@Param("start") int start, @Param("count")int count);
}

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.CategoryMapper;
import com.how2java.pojo.Category;
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();

        CategoryMapper mapper = session.getMapper(CategoryMapper.class);
        List<Category>  cs =mapper.listByPage(0, 5);
        for (Category c : cs) {System.out.println(c);
        }
        session.commit();
        session.close();}
}

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