<mappers>
<mapper resource="com/daniel/dao/IUserDao.xml"/>
<mapper resource="com/daniel/dao/IAccountDao.xml"/>
</mappers>
<mappers>
<package name="com.daniel.dao">package>
mappers>
查询所有账户的时候同时获得当前账户的所有信息(多表查询常用方法)
sql 语句查询所有账户的时候同时获得当前账户的所有信息 findAll
select u.*,a.id as aid,a.uid,a.money from account a ,user u where u.id=a.uid;
sql 语句查询所有账户的时候同时获得当前账户的所地址和姓名
select a.*,u.username,u.address from account a ,user u where u.id=a.uid;
在Account类中
//从表实体应该包含一个主表实体的对象引用
private User user;
public User getUser() {
return user;
}
public void setUser(User user) {
this.user = user;
}
//查询所有账户
List<Account> findAll();
<resultMap id="accountUserMap" type="Account">
<id property="id" column="aid">id>
<result property="uid" column="uid">result>
<result property="money" column="money">result>
<association property="user" column="uid" javaType="User">
<id property="id" column="id">id>
<result property="username" column="username">result>
<result property="sex" column="sex">result>
<result property="address" column="address">result>
<result property="birthday" column="birthday">result>
association>
resultMap>
<select id="findAll" resultMap="accountUserMap">
select u.*,a.id as aid,a.uid,a.money from account a ,user u where u.id=a.uid;
select>
注意事项中的 javaType=“User” 一定要指名主体表的实体类名 然后column中指名从表的外键!!
<association property="user" column="uid" javaType="User">
@Test
public void findAll(){
List<Account> accounts = accoutDao.findAll();
for (Account account:
accounts) {
System.out.println("每一个account的信息");
System.out.println(account);
System.out.println(account.getUser());
}
}
由于不常用就不细叙了
主表实体中应该包含从表实体的集合引用
select * from user u left outer join account a on u.id = a.uid
left join(左连接)是 left outer join的简写,返回左表中所有记录和右表中连接字段相等的记录,即返回的记录数和左表的记录数一样
User类中
//主表实体中应该包含从表实体的集合引用
private List<Account> accounts;
// 查询所有用户
List<User> findAll();
<resultMap id="userAccountMap" type="User">
<id property="id" column="id">id>
<result property="username" column="username">result>
<result property="sex" column="sex">result>
<result property="address" column="address">result>
<result property="birthday" column="birthday">result>
<collection property="accounts" ofType="Account">
<id property="id" column="aid">id>
<result property="uid" column="uid">result>
<result property="money" column="money">result>
collection>
resultMap>
<select id="findAll" resultMap="userAccountMap">
select * from user u left outer join account a on u.id = a.uid
select>
//查询所有(一个用户下的账号信息)
@Test
public void findAll( ) throws Exception {
List<User> users = userDao.findAll();
for (User user:users
) {
System.out.println("每个用户的信息");
System.out.println(user);
System.out.println(user.getAccounts());
}
}
select u.*,r.id as rid,r.role_name,r.role_desc from role r
left outer join user_role ur on r.id = ur.rid
left outer join user u on u.id=ur.uid
注意其中每行末尾的空格
分析 从role表中 为准的 左表( role r)中所有记录和右表(user_role ur)中连接字段相等的记录,即返回的记录数和左表的记录数一样(而且还可以输出不关联的行)再以此合并的表为基础( role r user_role ur )中连接和右表( user u )中连接字段相等的记录
多表外链接查询语句
use+数据库
select+查询列名
from+表1
left/right (outer) join +表2
由于是多对多的关系所有不分从表和主表
//多对多的关系映射:一个角色可以赋予多个用户
private List<User> users;
public List<User> getUsers() {
return users;
}
public void setUsers(List<User> users) {
this.users = users;
}
List<Role> findAll();
<resultMap id="roleMap" type="role">
<id property="roleId" column="rid">id>
<result property="roleName" column="role_name">result>
<result property="roleDesc" column="role_desc">result>
<collection property="users" ofType="user">
<id property="id" column="id">id>
<result property="username" column="username">result>
<result property="address" column="address">result>
<result property="sex" column="sex">result>
<result property="birthday" column="birthday">result>
collection>
resultMap>
<select id="findAll" resultMap="roleMap">
select u.*,r.id as rid,r.role_name,r.role_desc from role r
left outer join user_role ur on r.id = ur.rid
left outer join user u on u.id=ur.uid
select>
@Test
public void findAll(){
List<Role> roles = roleDao.findAll();
for (Role role:roles
) {
System.out.println("=====每个角色的信息=====");
System.out.println(role);
System.out.println(role.getUsers());
}
}
select u.*,r.id as rid,r.role_name,r.role_desc from user u
left outer join user_role ur on u.id = ur.uid
left outer join role r on r.id=ur.rid
private List<Role> roles;
public List<Role> getRoles() {
return roles;
}
public void setRoles(List<Role> roles) {
this.roles = roles;
}
// 查询所有
List<User> findAll();
<resultMap id="userMap" type="user">
<id property="id" column="id"></id>
<result property="username" column="username"></result>
<result property="address" column="address"></result>
<result property="sex" column="sex"></result>
<result property="birthday" column="birthday"></result>
<collection property="roles" ofType="role">
<id property="roleId" column="rid"></id>
<result property="roleName" column="role_name"></result>
<result property="roleDesc" column="role_desc"></result>
</collection>
</resultMap>
<select id="findAll" resultMap="userMap">
select u.*,r.id as rid,r.role_name,r.role_desc from user u
left outer join user_role ur on u.id = ur.uid
left outer join role r on r.id=ur.rid
</select>
@Test
public void findAll( ) throws Exception {
List<User> users = userDao.findAll();
for (User user:users
) {
System.out.println("====每个用户的信息====");
System.out.println(user);
System.out.println(user.getRoles());
}
}