关于后端:Mybatis系列教材-二-基础-CRUD

步骤1:先运行，看到成果，再学习
步骤2:模拟和排错
步骤3:在前一步的根底上进行
步骤4:配置文件Category.xml
步骤5:减少
步骤6:删除
步骤7:获取
步骤8:批改
步骤9:查问所有

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 : 在前一步的根底上进行

这一个知识点解说通过Mybatis进行CRUD一套操作，建设在上一个知识点Mybatis 入门教程的根底上进行。

步骤 4 : 配置文件Category.xml

首先一次性批改配置文件Category.xml，提供CRUD对应的sql语句。
每个SQL如何应用在后续对应操作里一一解说。

<?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_             </select></mapper>

步骤 5 : 减少

运行之后，如图所示能够看到 通过Mybatis查问进去的数据里有新减少的Category

通过session.insert调用addCategory对应的SQL语句

Category c = new Category();c.setName("新减少的Category");session.insert("addCategory", c);

addCategory对应的插入sql语句，#{name}会主动获取c对象的name属性值

<insert id="addCategory" parameterType="Category" >    insert into category_ ( name ) values (#{name})</insert>

• TestMybatis.java
• 代码片段1

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();        Category c = new Category();        c.setName("新减少的Category");        session.insert("addCategory", c);        listAll(session);        session.commit();        session.close();    }    private static void listAll(SqlSession session) {        List<Category> cs = session.selectList("listCategory");        for (Category c : cs) {            System.out.println(c.getName());        }    }}<insert id="addCategory" parameterType="Category" >    insert into category_ ( name ) values (#{name})   </insert>

步骤 6 : 删除

删除id=6的对象

Category c = new Category();c.setId(6);session.delete("deleteCategory",c);

deleteCategory对应删除的sql语句

<delete id="deleteCategory" parameterType="Category" >    delete from category_ where id= #{id}</delete>

• TestMybatis.java
• 代码片段1

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();        Category c = new Category();        c.setId(6);        session.delete("deleteCategory", c);        listAll(session);        session.commit();        session.close();    }    private static void listAll(SqlSession session) {        List<Category> cs = session.selectList("listCategory");        for (Category c : cs) {            System.out.println(c.getName());        }    }}<delete id="deleteCategory" parameterType="Category" >    delete from category_ where id= #{id}  </delete>

步骤 7 : 获取

通过session.selectOne获取id=3的记录

Category c= session.selectOne("getCategory",3);

getCategory对应的sql语句：

<select id="getCategory" parameterType="_int" resultType="Category">    select * from   category_  where id= #{id}</select>

• TestMybatis.java
• 代码片段1

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();        Category c = session.selectOne("getCategory", 3);        System.out.println(c.getName());//      listAll(session);        session.commit();        session.close();    }    private static void listAll(SqlSession session) {        List<Category> cs = session.selectList("listCategory");        for (Category c : cs) {            System.out.println(c.getName());        }    }}<select id="getCategory" parameterType="_int" resultType="Category">    select * from   category_  where id= #{id}   </select>

步骤 8 : 批改

通过session.update进行批改

session.update("updateCategory",c);

updateCategory对应的sql语句：

<update id="updateCategory" parameterType="Category" >    update category_ set name=#{name} where id=#{id}</update>

• TestMybatis.java
• 代码片段1

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();        Category c = session.selectOne("getCategory", 3);        c.setName("批改了的Category名稱");        session.update("updateCategory", c);        listAll(session);        session.commit();        session.close();    }    private static void listAll(SqlSession session) {        List<Category> cs = session.selectList("listCategory");        for (Category c : cs) {            System.out.println(c.getName());        }    }}<update id="updateCategory" parameterType="Category" >    update category_ set name=#{name} where id=#{id}   </update>

步骤 9 : 查问所有

session.selectList执行查问语句

List<Category> cs = session.selectList("listCategory");

listCategory对应的sql语句

<select id="listCategory" resultType="Category">    select * from   category_</select>

• TestMybatis.java
• 代码片段1

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();        listAll(session);        session.commit();        session.close();    }    private static void listAll(SqlSession session) {        List<Category> cs = session.selectList("listCategory");        for (Category c : cs) {            System.out.println(c.getName());        }    }}<select id="listCategory" resultType="Category">    select * from   category_</select>

更多内容，点击理解： https://how2j.cn/k/mybatis/mybatis-crud/1088.html