文章目录
Mybatis第三章
一、内容介绍
- mybatis自带数据源
- 事务问题
- 动态的sql语句：if标签和循环标签
- 多表之间的关系配置
一对一
一对多
多对多
二、mybatis自带数据源
<!--数据库的环境:
default； 指定默认的环境
-->
<environments default="development">
<!--id: 环境唯一的标志 -->
<environment id="development">
<!--事务管理： jdbc-->
<transactionManager type="JDBC"/>
<!--
dataSource: 数据源（数据库连接池）配置
type="POOLED" ： 数据源的类型配置
POOLED :使用mybatis的自带数据源配置
UNPOOLED: 不使用数据源配置， 使用Connection操作数据库
JNDI:JNDI服务 数据源配置
-->
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://localhost:3306/mybatisdb_sgw"/>
<property name="username" value="root"/>
<property name="password" value="root"/>
</dataSource>
</environment>
</environments>
三、事务问题
package com.sgw;
import com.sgw.domain.User;
import org.junit.Test;
import java.sql.*;
import java.util.ArrayList;
import java.util.List;
/**
* 回顾jdbc代码
*/
public class TestJDBC {
@Test
public void test(){
List<User> userList = new ArrayList<>();
//1. 注册驱动
try {
Class.forName("com.mysql.jdbc.Driver");
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
String url = "jdbc:mysql://localhost:3306/mybatisdb_sgw";
String username = "root";
String password = "root";
Connection conn = null;
PreparedStatement pst = null;
ResultSet rs = null;
try {
//2. 获取连接
conn = DriverManager.getConnection(url, username ,password);
//事务1 ：设置事务手动提交（不能自动提交）
conn.setAutoCommit(false);
// 3. SQL语句
String sql1 = "insert into ......";
String sql2 = "insert into ......";
//4. 创建statement对象: Statement , PreparedStatement
pst = conn.prepareStatement(sql1);
//5. 执行SQL语句，返回结果集
pst.executeUpdate();
pst = conn.prepareStatement(sql2);
pst.executeUpdate();
//事务2：提交事务
conn.commit();
} catch (SQLException e) {
//事务3：出现异常，回顾
try {
conn.rollback();
} catch (SQLException e1) {
e1.printStackTrace();
}
e.printStackTrace();
} finally {
//事务4： 还原状态，设置事务为自动提交
if(conn != null){
try {
conn.setAutoCommit(true);
} catch (SQLException e) {
e.printStackTrace();
}
}
//7. 释放资源: 先开后关
if(rs != null){
try {
rs.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if(pst != null){
try {
pst.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if(conn != null){
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
//打印结果
for (User user : userList) {
System.out.println(user);
}
}
}
四、动态sql语句
1、问题
<!--
多条件查询
如果传递参数个数不对，会出现异常，动态sql可以解决
-->
<select id="findByCondition" resultMap="users" parameterType="user">
select * from user where uname like "%"#{username}"%" and sex = #{sex}
</select>
2、if语句
<!--
多条件查询
-->
<select id="findByCondition" resultMap="users" parameterType="user">
select * from user where 1=1
<if test="username != null">
and uname like "%"#{username}"%"
</if>
<if test="sex != null">
and sex = #{sex}
</if>
</select>
3、where语句
<!--
where : 帮助程序员处理第一个and
多条件 都写上 and关键字
-->
<select id="findByCondition" resultMap="users" parameterType="user">
select * from user
<where>
<if test="username != null">
and uname like "%"#{username}"%"
</if>
<if test="sex != null">
and sex = #{sex}
</if>
</where>
</select>
4、SQL片段
<!--SQL片段
把重复的sql语句提取出来,需要使用时引用即可
id="": 唯一标志
文本：sql语句
-->
<sql id="select_user">select * from user</sql>
-- 关联使用sql片段
-- include :包含
-- refid: 关联的sql片段的id
-- ref ：references
<include refid="select_user"></include>
5、foreach语句
<delete id="delByArray" parameterType="integer[]">
delete from user where
<!--
foreach循环标签
collection: 参数的类型：如果是集合：list,如果是数组： array
open :前缀
close:后缀
separator: 分隔符
item: 循环中的每一个对象
index:循环中的索引（ 一般不用）
-->
<foreach collection="array" open="uid in (" close=")" separator="," item="id">
#{id}
</foreach>
</delete>
<delete id="delByList" parameterType="list">
delete from user where
<!--
foreach循环标签
collection: 参数的类型：如果是集合：list,如果是数组： array
open :前缀
close:后缀
separator: 分隔符
item: 循环中的每一个对象
index:循环中的索引（ 一般不用）
-->
<foreach collection="list" open="uid in (" close=")" separator="," item="id">
#{id}
</foreach>
</delete>
五、多表关联
1、一对一
a、第一种方法：accountUser extends Account
1）配置文件配置
<resultMap id="accountUsers" type="accountUser">
<result column="uname" property="username"></result>
</resultMap>
<select id="findAllAccountUser" resultMap="accountUsers">
select * from account a, user u where a.u_id = u.uid
</select>
2) pojo配置
/**
* 继承了Account，就拥有Account中所有的属性
* 单独添加User的属性
*/
public class AccountUser extends Account {
private Integer uid;
private String username;
private String password;
private String address;
private Date birthday;
private String sex;
}
3) Dao接口
/**
* 查询所有的账户:包含对应的用户信息
* @return
*/
public List<AccountUser> findAllAccountUser();
b、第二种方法
1)配置文件
<resultMap id="accounts" type="Account">
<id column="id" property="id"></id>
<result column="name" property="name"></result>
<result column="money" property="money"></result>
<result column="u_id" property="u_id"></result>
<!--映射user中的属性-->
<result column="uid" property="user.id"></result>
<result column="uname" property="user.username"></result>
<result column="address" property="user.address"></result>
<result column="birthday" property="user.birthday"></result>
<result column="sex" property="user.sex"></result>
<result column="password" property="user.password"></result>
</resultMap>
2)pojo
public class Account {
private Integer id;
private String name;
private Float money;
private Integer u_id;
// 一个账户对应一个用户
private User user;
}
3） Dao接口
/**
* 查询所有的账户:包含对应的用户信息
* @return
*/
public List<Account> findAllAccount();
c、第三种方法
1)配置文件
<resultMap id="accounts" type="Account">
<id column="id" property="id"></id>
<result column="name" property="name"></result>
<result column="money" property="money"></result>
<result column="u_id" property="u_id"></result>
<!--映射user中的属性-->
<!--association 映射单个对象
property：属性名
javaType:属性对应的类型
-->
<association property="user" javaType="user">
<id column="uid" property="id"></id>
<result column="uname" property="username"></result>
<result column="address" property="address"></result>
<result column="birthday" property="birthday"></result>
<result column="password" property="password"></result>
<result column="sex" property="sex"></result>
</association>
</resultMap>
2)pojo
public class Account {
private Integer id;
private String name;
private Float money;
private Integer u_id;
// 一个账户对应一个用户
private User user;
}
3） Dao接口
/**
* 查询所有的账户:包含对应的用户信息
* @return
*/
public List<Account> findAllAccount();
2、一对多
a. pojo
public class User {
private Integer id;
private String username;
private String password;
private String address;
private Date birthday;
private String sex;
//一个用户对应多个账户
private List<Account> accountList;
}
b. 配置文件
<resultMap id="users" type="User">
<id column="uid" property="id"></id>
<result column="uname" property="username"></result>
<result column="password" property="password"></result>
<result column="address" property="address"></result>
<result column="birthday" property="birthday"></result>
<result column="sex" property="sex"></result>
<!--Collection : 映射accountList 属性
property: 对应的属性名
ofType: 集合中的元素类型: association 中javaType效果一致
-->
<collection property="accountList" ofType="account">
<id column="id" property="id"></id>
<result column="name" property="name"></result>
<result column="money" property="money"></result>
<result column="u_id" property="u_id"></result>
</collection>
</resultMap>
<select id="findAll" resultMap="users">
select * from user u left join account a on u.uid = a.u_id
</select>
c、Dao接口
/**
* 返回所有的user对象，包含用户对应账户信息
* @return
*/
public List<User> findAll();
3、多对多
a. sql语句
create table role(
id int primary key auto_increment,
roleName varchar(20),
roleDesc varchar(20)
)
create table user_role(
uid int ,
rid int ,
-- 联合主键: 两列以上为主键列, 两列不能同时相同
primary key(uid,rid),
foreign key(uid) references user(uid),
foreign key(rid) references role(id)
)
b. pojo
public class User {
private Integer id;
private String username;
private String password;
private String address;
private Date birthday;
private String sex;
// 一个用户有多个角色
private List<Role> roleList;
}
c、配置文件
<mapper namespace="com.sgw.dao.UserDao">
<resultMap id="users" type="user">
<id column="uid" property="id"></id>
<result column="uname" property="username"></result>
<result column="address" property="address"></result>
<result column="birthday" property="birthday"></result>
<result column="sex" property="sex"></result>
<result column="password" property="password"></result>
<!--一个用户对应多个角色: roleList-->
<collection property="roleList" ofType="role">
<id column="id" property="id"></id>
<result column="roleName" property="roleName"></result>
<result column="roleDesc" property="roleDesc"></result>
</collection>
</resultMap>
<select id="findAll" resultMap="users">
select u.* ,r.* from user u left join user_role ur on u.uid = ur.uid left join role r on r.id = ur.rid
</select>
</mapper>
d、dao接口
/**
* 返回所有的user对象，包含用户对应的角色对象
* @return
*/
public List<User> findAll();
角色到用户的关系
a、pojo
public class Role {
private Integer id;
private String roleName;
private String roleDesc;
// 一个角色对应多个用户'
private List<User> userList;
}
b、配置文件
<mapper namespace="com.sgw.dao.RoleDao">
<resultMap id="roles" type="role">
<id column="id" property="id"></id>
<result column="roleName" property="roleName"></result>
<result column="roleDesc" property="roleDesc"></result>
<collection property="userList" ofType="User">
<id column="uid" property="id"></id>
<result column="uname" property="username"></result>
<result column="address" property="address"></result>
<result column="birthday" property="birthday"></result>
<result column="sex" property="sex"></result>
<result column="password" property="password"></result>
</collection>
</resultMap>
<select id="findAll" resultMap="roles">
select r.*,u.* from role r left join user_role ur on r.id = ur.rid left join user u on u.uid = ur.uid
</select>
</mapper>
c、dao接口
/**
* 查询所有的角色，包含用户对象
* @return
*/
public List<Role> findAll();
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