HQL Join - 加入的路径！过冬 [英] HQL Join - Path expected for join! hibernate
问题描述
我是hibernate的新手，遇到以下问题：
当我尝试运行此查询时，出现了期望加入的路径！异常。
String hql =从票证中选择avg（t.price）t JOIN Flight f WHERE f.number ='+ flightNumber +';
查询查询= this.session.createQuery（hql）;
列表< Double> list = query.list（）;
我想选择某个航班已售出机票的平均价格。
我检查了这些链接，但我没有解决我的问题：
HQL左连接：加入的路径
hql内部联接加入的路径！错误
我的代码是：
Flight.hbm.xml
<？xml version =1.0？><！DOCTYPE hibernate-mapping PUBLIC
- // Hibernate / Hibernate映射DTD 3.0 // EN
http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd\">
< hibernate-mapping>
< class name =pck.Flighttable =flightcatalog =airbook>
< id name =idtype =java.lang.Integer>
< column name =id/>
< generator class =identity/>
< / id>
< /多对一>
< /多对一>
< property name =numbertype =string>
< column name =numberlength =30/>
< / property>
< property name =datetype =timestamp>
< column name =datelength =19/>
< / property>
< property name =milestype =java.lang.Integer>
< column name =miles/>
< / property>
< property name =numberofseatstype =java.lang.Integer>
< column name =numberofseats/>
< / property>
< property name =airplanetype =string>
< column name =airplanelength =30/>
< / property>
< set name =ticketstable =ticketinverse =truelazy =truefetch =select>
< key>
< column name =flightid/>
< / key>
<一对多课程=pck.Ticket/>
< / set>
< / class> < /休眠映射>
Ticket.hbm.xml
<？xml version =1.0？> <！DOCTYPE hibernate-mapping PUBLIC - // Hibernate / Hibernate映射DTD 3.0 // EN
http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd\">
< hibernate-mapping>
< class name =pck.Tickettable =ticketcatalog =airbook>
< id name =idtype =java.lang.Integer>
< column name =id/>
< generator class =identity/>
< / id>
<多对一名称=飞行class =pck.Flightfetch =select>
< column name =flightid/>
< /多对一>
<多对一名称=乘客class =pck.Passengerfetch =select>
< column name =passengerid/>
< /多对一>
< property name =pricetype =java.lang.Double>
< column name =priceprecision =22scale =0/>
< / property>
< / class>
< / hibernate-mapping>
所有其他没有JOIN的查询都可以正常工作。我不知道问题出在哪里。
正确的查询是：
从Ticket中选择avg（t.price）t join t.flight f其中f.number =：flightNumber
并且一起执行查询：
事务tx = session.beginTransaction（）;
String hql =从Ticket中选择avg（t.price）t join t.flight f where f.number =：flightNumber;
查询查询= this.session.createQuery（hql）.setString（flightNumber，flightNumber）;
列表< Double> list = query.list（）;
tx.commit（）;
正如您所链接到的问题所解释的， Hibernate文档，连接使用实体之间的关联。所以正确的查询是：
从Ticket中选择avg（t.price）t join t.flight f where f.number =： flightNumber
另外请注意，使用参数比直接在查询中连接值要好得多。它自动处理引用和转义，并且没有任何HQL注入风险。
I am new to hibernate and I met a following problem: I got "Path expected for join!" exception when I tried to run this query:
String hql = "select avg(t.price) from Ticket t JOIN Flight f WHERE f.number = '" + flightNumber + "'";
Query query = this.session.createQuery(hql);
List<Double> list = query.list();
I wanted to select average price of tickets that have been sold for a given flight.
I have checked these links, but I did not solve my problem: HQL left join: Path expected for join hql inner join Path expected for join! error
My code is:
Flight.hbm.xml
<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="pck.Flight" table="flight" catalog="airbook">
<id name="id" type="java.lang.Integer">
<column name="id" />
<generator class="identity" />
</id>
<many-to-one name="sourceairport" class="pck.Sourceairport" fetch="select">
<column name="sourceairportid" />
</many-to-one>
<many-to-one name="destinationairport" class="pck.Destinationairport" fetch="select">
<column name="destinationairportid" />
</many-to-one>
<property name="number" type="string">
<column name="number" length="30" />
</property>
<property name="date" type="timestamp">
<column name="date" length="19" />
</property>
<property name="miles" type="java.lang.Integer">
<column name="miles" />
</property>
<property name="numberofseats" type="java.lang.Integer">
<column name="numberofseats" />
</property>
<property name="airplane" type="string">
<column name="airplane" length="30" />
</property>
<set name="tickets" table="ticket" inverse="true" lazy="true" fetch="select">
<key>
<column name="flightid" />
</key>
<one-to-many class="pck.Ticket" />
</set>
</class> </hibernate-mapping>
Ticket.hbm.xml
<?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="pck.Ticket" table="ticket" catalog="airbook">
<id name="id" type="java.lang.Integer">
<column name="id" />
<generator class="identity" />
</id>
<many-to-one name="flight" class="pck.Flight" fetch="select">
<column name="flightid" />
</many-to-one>
<many-to-one name="passenger" class="pck.Passenger" fetch="select">
<column name="passengerid" />
</many-to-one>
<property name="price" type="java.lang.Double">
<column name="price" precision="22" scale="0" />
</property>
</class>
</hibernate-mapping>
All the other queries without JOIN work fine. I do not know where the problem is.
The correct query is:
select avg(t.price) from Ticket t join t.flight f where f.number = :flightNumber
And altogether with query execution:
Transaction tx = session.beginTransaction();
String hql = "select avg(t.price) from Ticket t join t.flight f where f.number = :flightNumber";
Query query = this.session.createQuery(hql).setString("flightNumber", flightNumber);
List<Double> list = query.list();
tx.commit();
As explained in the question you linked to, and in the Hibernate documentation, joins use associations between entities. So the correct query is
select avg(t.price) from Ticket t join t.flight f where f.number = :flightNumber
Also note that using parameters is a much better solution than concatenating values directly in the query. It handles quoting and escaping automatically, and doesn't have any risk of HQL injection.
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