[英]Setting the value of a column according to the count() of the referred rows in another table to my table in SQL and hibernate mapping
我的数据库中有以下表格。 我想列booked_items
在testuser
表包含与该用户相关联的行数testbooking
表。 当然可以在程序内部完成,但是如果可以在休眠映射和表DDL中完成则很脏。
CREATE TABLE `testuser` (
`id` bigint(20) NOT NULL,
`username` varchar(30) DEFAULT NULL,
`password` varchar(128) DEFAULT NULL,
`booked_items` int(11) DEFAULT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `username` (`username`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
CREATE TABLE `testbooking` (
`id` bigint(20) NOT NULL AUTO_INCREMENT,
`user_id` bigint(20) NOT NULL,
`item_id` bigint(20) NOT NULL,
`start_date` date DEFAULT NULL,
`end_date` date DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `FKEC747367A12BE486` (`item_id`),
KEY `FKEC7473671463A66C` (`user_id`),
CONSTRAINT `FKEC7473671463A66C` FOREIGN KEY (`user_id`) REFERENCES `testuser`
(`id`),
CONSTRAINT `FKEC747367A12BE486` FOREIGN KEY (`item_id`) REFERENCES `testitem`
(`id`)
) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=latin1;
CREATE TABLE `testitem` (
`id` bigint(20) NOT NULL AUTO_INCREMENT,
`title` varchar(30) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=38 DEFAULT CHARSET=latin1;
testuser表的休眠映射为:
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="my.hibernate.actors.User" discriminator-value="user"
table="testuser" catalog="efeu">
<id name="id" type="java.lang.Long">
<column name="id" />
<generator class="increment" />
</id>
<discriminator column="user_type" type="string" length="8" />
<property name="username" type="java.lang.String" not-null="true"
unique="true" unique-key="true">
<column name="username" length="30" />
</property>
<property name="password" type="java.lang.String" not-null="true">
<column name="password" length="128" />
<subclass name="my.hibernate.actors.Subscriber"
discriminator-value="subsc">
<property name="bookedItems" type="java.lang.Integer" column="booked_items" />
<set name="bookings" inverse="true" cascade="all-delete-orphan">
<key column="user_id" />
<one-to-many class="my.hibernate.operations.Booking" />
</set>
</subclass>
<subclass name="my.hibernate.actors.Clerk"
discriminator-value="clerk" />
</class>
</hibernate-mapping>
testbooking表的休眠映射为:
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="my.hibernate.operations.Booking" table="testBooking" catalog="efeu">
<id name="id" type="java.lang.Long">
<column name="id" />
<generator class="native" />
</id>
<many-to-one name="userID" column="user_id" cascade="persist"
not-null="true" class="my.hibernate.actors.Subscriber" />
<many-to-one name="itemID" column="item_id" cascade="persist"
not-null="true" class="my.hibernate.items.Item" />
<property name="startDate" type="java.sql.Date" not-null="true">
<column name="start_date" length="10" />
</property>
<property name="endDate" type="java.sql.Date">
<column name="end_date" length="10" />
</property>
</class>
</hibernate-mapping>
PS。 我想问两个独立的问题。 一次用于Hibernate,一次用于SQL,但我担心它将被视为重复项。 对于Hibernate需要了解的SQL我很感兴趣。 并且它取决于SQL的方言吗? 我目前正在询问mysql方言。
您可以在用户类上使用与SQL公式关联的属性。
<property name="booked_items" type="long" formula="(SELECT COUNT(tb.id) FROM testbooking AS tb WHERE tb.user_id = id)"/>
看看这个答案: 好像重复
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