MyBatis实践之动态SQL及关联查询

<code class=" hljs vbnet"><select id="selectUser" resulttype="com.fq.domain.User" parametertype="com.fq.domain.User">
SELECT * FROM user
AND id = #{id}
AND name = #{name}
AND password = #{password}
</select></code>

<code class="hljs vbnet"><code class="hljs php">List<user> selectUser(User user) throws Exception;</user></code></code>

<code class="hljs vbnet"><code class="hljs php"><code class="hljs java">@Test
public void selectUserClient() throws Exception {
UserDAO dao = session.getMapper(UserDAO.class);
User user = dao.selectUser(new User(null, null, "new_password"));
System.out.println(user);
}</code></code></code>

<code class=" hljs vbnet"><code class=" hljs php"><code class=" hljs java"><code class=" hljs vbnet"><select id="selectUser" resulttype="com.fq.domain.User" parametertype="com.fq.domain.User">
SELECT * FROM user
AND id = #{id}
AND name = #{name}
AND password = #{password}
</select></code></code></code></code>

<code class="hljs vbnet"><code class="hljs php"><code class="hljs java"><code class="hljs vbnet"><code class="hljs applescript"><update id="updateUserById" parametertype="com.fq.domain.User">
UPDATE user
<set>
<if test="name != null">
name = #{name} ,
</if>
<if test="password != null">
password = #{password} ,
</if>
</set>
WHERE id = #{id};
</update></code></code></code></code></code>

<code class="hljs vbnet"><code class="hljs php"><code class="hljs java"><code class="hljs vbnet"><code class="hljs applescript"><code class="hljs sql">SELECT * FROM user WHERE (id = "htmlcode">

<code class=" hljs vbnet"><code class=" hljs php"><code class=" hljs java"><code class=" hljs vbnet"><code class=" hljs applescript"><code class=" hljs sql"><code class=" hljs cs"><select id="selectUser" parametertype="java.util.List" resulttype="com.fq.domain.User">
SELECT *
FROM user
id = #{id}
</select></code></code></code></code></code></code></code>
<code class=" hljs vbnet"><code class=" hljs php"><code class=" hljs java"><code class=" hljs vbnet"><code class=" hljs applescript"><code class=" hljs sql"><code class=" hljs cs"><code class=" hljs cs"><select id="selectUser" parametertype="java.util.List" resulttype="com.fq.domain.User">
SELECT *
FROM user
#{id}
</select></code></code></code></code></code></code></code></code>


元素 描述


collection SQL解析的参数名

index 循环下标

item 单个元素的名

open 循环开始输出

close 循环结束输出

separator 中间分隔输出
传递List作为parameterType时,SQL解析参数名固定为list.
UserDAO


<code class="hljs vbnet"><code class="hljs php"><code class="hljs java"><code class="hljs vbnet"><code class="hljs applescript"><code class="hljs sql"><code class="hljs cs"><code class="hljs cs"><code class="hljs mathematica">List<user> selectUser(List<integer> ids) throws Exception;</integer></user></code></code></code></code></code></code></code></code></code>


批量插入用户案例
mapper


<code class="hljs vbnet"><code class="hljs php"><code class="hljs java"><code class="hljs vbnet"><code class="hljs applescript"><code class="hljs sql"><code class="hljs cs"><code class="hljs cs"><code class="hljs mathematica"><code class="hljs xml"><insert id="insertUserList" parametertype="java.util.List">
INSERT INTO user(name, password) VALUES
<if test="list != null and list.size != 0">
<foreach collection="list" item="user" separator=",">
(#{user.name}, #{user.password})
</foreach>
</if>
</insert></code></code></code></code></code></code></code></code></code></code>


UserDAO


<code class="hljs vbnet"><code class="hljs php"><code class="hljs java"><code class="hljs vbnet"><code class="hljs applescript"><code class="hljs sql"><code class="hljs cs"><code class="hljs cs"><code class="hljs mathematica"><code class="hljs xml"><code class="hljs java">void insertUserList(List<user> users) throws Exception;</user></code></code></code></code></code></code></code></code></code></code></code>


Client


<code class="hljs vbnet"><code class="hljs php"><code class="hljs java"><code class="hljs vbnet"><code class="hljs applescript"><code class="hljs sql"><code class="hljs cs"><code class="hljs cs"><code class="hljs mathematica"><code class="hljs xml"><code class="hljs java"><code class="hljs java">@Test
public void insertUserListClient() throws Exception {
UserDAO dao = session.getMapper(UserDAO.class);
dao.insertUserList(Lists.newArrayList(new User(null, "mojia5", "mojia5"), new User(null, "mojia6", "mojia6"), new User(null, "mojia7", "mojia7")));
}</code></code></code></code></code></code></code></code></code></code></code></code>


传入数组
mapper


<code class=" hljs vbnet"><code class=" hljs php"><code class=" hljs java"><code class=" hljs vbnet"><code class=" hljs applescript"><code class=" hljs sql"><code class=" hljs cs"><code class=" hljs cs"><code class=" hljs mathematica"><code class=" hljs xml"><code class=" hljs java"><code class=" hljs java"><code class=" hljs cs"><select id="selectUser" parametertype="Object[]" resulttype="com.fq.domain.User">
SELECT *
FROM user
#{id}
</select></code></code></code></code></code></code></code></code></code></code></code></code></code>


与List类似,传递数组作为parameterType时,SQL解析参数名固定为array.
UserDAO


<code class="hljs vbnet"><code class="hljs php"><code class="hljs java"><code class="hljs vbnet"><code class="hljs applescript"><code class="hljs sql"><code class="hljs cs"><code class="hljs cs"><code class="hljs mathematica"><code class="hljs xml"><code class="hljs java"><code class="hljs java"><code class="hljs cs"><code class="hljs mathematica">List<user> selectUser(Integer[] ids) throws Exception;</user></code></code></code></code></code></code></code></code></code></code></code></code></code></code>


SQL片段
可以将一段公共的SQL语句抽取出来, 作为一个SQL片段, 供其他SQL调用:


<code class=" hljs vbnet"><code class=" hljs php"><code class=" hljs java"><code class=" hljs vbnet"><code class=" hljs applescript"><code class=" hljs sql"><code class=" hljs cs"><code class=" hljs cs"><code class=" hljs mathematica"><code class=" hljs xml"><code class=" hljs java"><code class=" hljs java"><code class=" hljs cs"><code class=" hljs mathematica"><code class=" hljs vbnet"><sql id="user_where">
<if test="id != null">
AND id = #{id}
</if>
<if test="name != null">
AND name = #{name}
</if>
<if test="password != null">
AND password = #{password}
</if>
</sql>
<select id="selectUser" resulttype="com.fq.domain.User" parametertype="com.fq.domain.User">
SELECT * FROM user
</select></code></code></code></code></code></code></code></code></code></code></code></code></code></code></code>


经验:最好基于单表定义SQL片段,而且在SQL片段中不要包含/之类的标签,这样可以保证SQL片段重用度更高.
关联查询
数据模型分析思路
每张表的数据内容:分模块对每张表记录的内容进行熟悉,相当于学习系统需求/功能. 每张表重要的字段:非空字段/外键字段等. 表与表之间的数据库级别关系: 外键关系. 表与表之间的业务关系:建立在某个业务的基础上去分析.
订单/商品数据模型



表内容


user: 购买商品的用户信息 order: 用户创建的订单 orderdetail: 订单详细(购买商品信息) item: 商品信息 表与表之间的业务关系:


user/order:

user -> order: 一对多 order -> user: 一对一 order/orderdetail:

order -> orderdetail:一对多 orderdetail -> order:一对一 orderdetail/item:

orderdetail -> item:一对一 item -> orderdetail:一对多


‘一对一'查询
需求: 查询订单信息,关联查询(创建订单的)用户信息.
由以上分析可知主查询为order表,而order -> user关系为一对一, 因此使用resultMap将查询结果的订单信息映射到Order中,将用户信息映射到Order中的User属性.
PO: 改造User


<code class="hljs vbnet"><code class="hljs php"><code class="hljs java"><code class="hljs vbnet"><code class="hljs applescript"><code class="hljs sql"><code class="hljs cs"><code class="hljs cs"><code class="hljs mathematica"><code class="hljs xml"><code class="hljs java"><code class="hljs java"><code class="hljs cs"><code class="hljs mathematica"><code class="hljs vbnet"><code class="hljs java">public class User implements Serializable {
private Integer id;
private String username;
private Date birthday;
private Integer sex;
private String address;
// ..
}</code></code></code></code></code></code></code></code></code></code></code></code></code></code></code></code>


PO: 新增Order, 将User组合到Order中:


<code class="hljs vbnet"><code class="hljs php"><code class="hljs java"><code class="hljs vbnet"><code class="hljs applescript"><code class="hljs sql"><code class="hljs cs"><code class="hljs cs"><code class="hljs mathematica"><code class="hljs xml"><code class="hljs java"><code class="hljs java"><code class="hljs cs"><code class="hljs mathematica"><code class="hljs vbnet"><code class="hljs java"><code class="hljs java">public class Order implements Serializable {
private Integer id;
private Integer userId;
private String number;
private Date createTime;
private String note;
private User user;
// ...
}</code></code></code></code></code></code></code></code></code></code></code></code></code></code></code></code></code>


mapper


<code class=" hljs vbnet"><code class=" hljs php"><code class=" hljs java"><code class=" hljs vbnet"><code class=" hljs applescript"><code class=" hljs sql"><code class=" hljs cs"><code class=" hljs cs"><code class=" hljs mathematica"><code class=" hljs xml"><code class=" hljs java"><code class=" hljs java"><code class=" hljs cs"><code class=" hljs mathematica"><code class=" hljs vbnet"><code class=" hljs java"><code class=" hljs java"><code class=" hljs xml"><!--{cke_protected}{C}%3C!%2D%2D%3Fxml%20version%3D%221.0%22%20encoding%3D%22UTF-8%22%20%3F%2D%2D%3E-->
<mapper namespace="com.fq.mybatis.OrderDAO">
<cache type="org.mybatis.caches.ehcache.EhcacheCache">
<resultmap id="order_user_map" type="com.fq.domain.Order">
<id column="id" property="id">
<result column="user_id" property="userId">
<result column="number" property="number">
<result column="create_time" property="createTime">
<result column="note" property="note">
<association property="user" javatype="com.fq.domain.User">
<id column="user_id" property="id">
<result column="username" property="username">
<result column="birthday" property="birthday">
<result column="sex" property="sex">
<result column="address" property="address">
</result></result></result></result></id></association>
</result></result></result></result></id></resultmap>
<select id="selectOrderWithUser" resultmap="order_user_map">
SELECT
`order`.*,
username,
birthday,
sex,
address
FROM `order`, user
WHERE `order`.user_id = user.id AND `order`.id = #{0};
</select>
</cache></mapper></code></code></code></code></code></code></code></code></code></code></code></code></code></code></code></code></code></code>
association: 映射关联查询的单条记录(将关联查询信息映射到PO对象属性).


OrderDAO


<code class="hljs vbnet"><code class="hljs php"><code class="hljs java"><code class="hljs vbnet"><code class="hljs applescript"><code class="hljs sql"><code class="hljs cs"><code class="hljs cs"><code class="hljs mathematica"><code class="hljs xml"><code class="hljs java"><code class="hljs java"><code class="hljs cs"><code class="hljs mathematica"><code class="hljs vbnet"><code class="hljs java"><code class="hljs java"><code class="hljs xml"><code class="hljs cs">public interface OrderDAO {
Order selectOrderWithUser(Integer id) throws Exception;
}</code></code></code></code></code></code></code></code></code></code></code></code></code></code></code></code></code></code></code>


Client


<code class="hljs vbnet"><code class="hljs php"><code class="hljs java"><code class="hljs vbnet"><code class="hljs applescript"><code class="hljs sql"><code class="hljs cs"><code class="hljs cs"><code class="hljs mathematica"><code class="hljs xml"><code class="hljs java"><code class="hljs java"><code class="hljs cs"><code class="hljs mathematica"><code class="hljs vbnet"><code class="hljs java"><code class="hljs java"><code class="hljs xml"><code class="hljs cs"><code class="hljs java">@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = "classpath:spring/applicationContext.xml")
public class OrderDAOClient {
@Autowired
private OrderDAO dao;
@Test
public void client() throws Exception {
Order order = dao.selectOrderWithUser(3);
System.out.println(order);
}
}</code></code></code></code></code></code></code></code></code></code></code></code></code></code></code></code></code></code></code></code>


‘一对多'查询
需求: 查询订单及订单明细的信息(一对多).
PO: 定义OrderDetail,并在Order中添加List orderDetails订单明细属性:


<code class="hljs java">public class OrderDetail implements Serializable {
private Integer id;
private Integer orderId;
private Integer itemId;
private Integer itemNumber;
// ...
}</code>


mapper


<code class=" hljs java"><code class=" hljs vbnet"><resultmap id="order_user_detail_map" type="com.fq.domain.Order" extends="order_user_map">
<collection property="orderDetails" oftype="com.fq.domain.OrderDetail">
<id column="order_detail_id" property="id">
<result column="item_id" property="itemId">
<result column="item_num" property="itemNumber">
<result column="order_id" property="orderId">
</result></result></result></id></collection>
</resultmap>
<select id="selectOrderWithDetail" resultmap="order_user_detail_map">
SELECT
`order`.*,
username,
birthday,
sex,
address,
orderdetail.id order_detail_id,
item_id,
item_num,
order_id
FROM `order`, user, orderdetail
WHERE `order`.user_id = user.id AND `order`.id = orderdetail.order_id AND `order`.id = #{0};
</select></code></code>


元素 描述
property 指定关联查询的结果集存储到的属性
ofType 指定关联查询结果集中的对象类型OrderDAO


<code class="hljs java"><code class="hljs vbnet"><code class="hljs mathematica">Order selectOrderWithDetail(Integer id) throws Exception;</code></code></code>


‘多对多'查询


需求: 查询用户及用户购买商品信息.
由于User表与Item表没有直接关联,因此只能通过Order表与OrderDetail表进行关联.
思路:


1) 将用户信息映射到User中.

2) 在User中添加List订单列表属性,将用户创建的订单映射到orders.

3) 在Order中添加List订单明细列表属性,将订单的明细映射到orderDetails.

4) 在OrderDetail中添加Item属性,将订单明细所对应的商品映射到item.
PO: Item


<code class="hljs java"><code class="hljs vbnet"><code class="hljs mathematica"><code class="hljs cs">public class Item {
private Integer id;
private String name;
private Float price;
private String detail;
private String pic;
private Date createTime;
//...
}</code></code></code></code>


mapper



<code class=" hljs java"><code class=" hljs vbnet"><code class=" hljs mathematica"><code class=" hljs cs"><code class=" hljs applescript"><resultmap id="user_item_map" type="com.fq.domain.User">
<id column="id" property="id">
<result column="username" property="username">
<result column="birthday" property="birthday">
<result column="sex" property="sex">
<result column="address" property="address">
<collection property="orders" oftype="com.fq.domain.Order">
<id column="order_id" property="id">
<result column="id" property="userId">
<result column="order_create_time" property="createTime">
<result column="order_note" property="note">
<result column="order_number" property="number">
<collection property="orderDetails" oftype="com.fq.domain.OrderDetail">
<id column="order_detail_id" property="id">
<result column="order_id" property="orderId">
<result column="item_id" property="itemId">
<result column="order_item_num" property="itemNumber">
<association property="item" javatype="com.fq.domain.Item">
<id column="item_id" property="id">
<result column="item_create_time" property="createTime">
<result column="item_detail" property="detail">
<result column="item_name" property="name">
<result column="item_price" property="price">
<result column="item_pic" property="pic">
</result></result></result></result></result></id></association>
</result></result></result></id></collection>
</result></result></result></result></id></collection>
</result></result></result></result></id></resultmap>
<select id="selectUserItem" resultmap="user_item_map">
SELECT
user.*,
`order`.id order_id,
`order`.create_time order_create_time,
`order`.note order_note,
`order`.number order_number,
orderdetail.id order_detail_id,
orderdetail.item_num order_item_num,
item.id item_id,
item.create_time item_create_time,
item.detail item_detail,
item.name item_name,
item.price item_price,
item.pic item_pic
FROM user, item, `order`, orderdetail
WHERE `order`.user_id = user.id AND orderdetail.order_id = `order`.id AND orderdetail.item_id = item.id ;
</select></code></code></code></code></code>


OrderDAO


<code class="hljs java"><code class="hljs vbnet">
<code class="hljs mathematica">
<code class="hljs cs">
<code class="hljs applescript">
<code class="hljs php">List<user> selectUserItem() throws Exception;</user>
</code></code></code></code></code></code>


resultMap小结:
使用和可以完成一对一和一对多的高级映射.
association: 将关联查询信息映射到一个PO对象中. collection: 将关联查询信息映射到一个集合中.


延迟加载
关联查询时,使用MyBatis 延迟加载 特性可有效减轻数据库压力.首次查询只查询主表信息,等需要时再去查询关联表信息.的/具备延迟加载功能.
需求: 查询订单信息并关联查询用户信息.
延迟加载开关
在MyBatis核心配置文件(mybatis-configuration.xml)中配置:


1) lazyLoadingEnabled : 设置是否懒加载.默认false,则所有关联查询都会被初始化加载.


2) aggressiveLazyLoading : 设置是否积极加载. 默认true,所有关联属性被初始化加载.
Settings配置:


<code class=" hljs java">
<code class=" hljs vbnet"><code class=" hljs mathematica">
<code class=" hljs cs"><code class=" hljs applescript"><code class=" hljs php">
<code class=" hljs xml"><settings>
<setting name="cacheEnabled" value="true">
<setting name="lazyLoadingEnabled" value="true">
<setting name="aggressiveLazyLoading" value="false">
</setting></setting></setting></settings></code></code></code></code></code></code></code>


Mapper
只查询订单信息


<code class=" hljs java"><code class=" hljs vbnet"><code class=" hljs mathematica"><code class=" hljs cs"><code class=" hljs applescript"><code class=" hljs php"><code class=" hljs xml"><code class=" hljs applescript"><resultmap id="order_user_map" type="com.fq.domain.Order">
<id column="id" property="id">
<result column="user_id" property="userId">
<result column="number" property="number">
<result column="create_time" property="createTime">
<result column="note" property="note">
<association property="user" javatype="com.fq.domain.User" select="com.fq.mybatis.UserDAO.selectUserById" column="user_id">
</association></result></result></result></result></id></resultmap>
<select id="selectOrderWithUser" resultmap="order_user_map">
SELECT *
FROM `order`;
</select></code></code></code></code></code></code></code></code>


元素 描述


select 指定关联查询Statement为com.fq.mybatis.UserDAO.selectUserById.


column 指定关联查询时将users_id值传入selectUserById.关联查询用户信息(namespace为com.fq.mybatis.UserDAO)


<code class=" hljs java"><code class=" hljs vbnet"><code class=" hljs mathematica"><code class=" hljs cs"><code class=" hljs applescript"><code class=" hljs php"><code class=" hljs xml"><code class=" hljs applescript"><code class=" hljs vbnet"><select id="selectUserById" parametertype="java.lang.Integer" resulttype="com.fq.domain.User">
SELECT *
FROM user
WHERE id = #{id};
</select></code></code></code></code></code></code></code></code></code>


将上面查询到的订单信息中的user_id传入selectUserById来关联查询用户信息.
OrderDAO(同前)


<code class="hljs java">
<code class="hljs vbnet">
<code class="hljs mathematica">
<code class="hljs cs">
<code class="hljs applescript">
<code class="hljs php">
<code class="hljs xml">
<code class="hljs applescript">
<code class="hljs vbnet">
<code class="hljs mathematica">List<order> selectOrderWithUser() throws Exception;</order>
</code>
</code></code></code></code></code></code></code></code></code>


Client


<code class="hljs java"><code class="hljs vbnet"><code class="hljs mathematica"><code class="hljs cs"><code class="hljs applescript"><code class="hljs php"><code class="hljs xml"><code class="hljs applescript"><code class="hljs vbnet"><code class="hljs mathematica"><code class="hljs java">@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = "classpath:spring/applicationContext.xml")
public class OrderDAOClient {
@Autowired
private OrderDAO dao;
@Test
public void client() throws Exception {
List<order> orders = dao.selectOrderWithUser();
for (Order order : orders) {
System.out.println(order.getUser());
}
}
}</order></code></code></code></code></code></code></code></code></code></code></code>


debug上面Client, 观察log信息,会发现只有当确实需要User信息时才会调用selectUserById.
以上所述是小编给大家介绍的mybatis实践之动态sql及关联查询，希望对大家以上帮助！