HQL加入 - 加入的路徑！休眠

Question

我是新來的休眠，我遇到了以下問題： 我得到了「加入的路徑！」例外，當我試圖運行此查詢：

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(); 

我想選擇已賣了給定機票的平均價格。

我已經檢查了這些鏈接，但我並沒有解決我的問題： HQL left join: Path expected for join hql inner join Path expected for join! error

我的代碼是：

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> 

所有其他沒有JOIN的查詢都可以正常工作。我不知道問題出在哪裏。

---

正確的查詢是：

select avg(t.price) from Ticket t join t.flight f where f.number = :flightNumber 

而且完全與查詢執行：

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(); 

Answer 1

如您鏈接到的問題說明，並在Hibernate documentation，加入之間利用關聯實體。所以正確的查詢是

select avg(t.price) from Ticket t join t.flight f where f.number = :flightNumber 

另外請注意，使用參數比在查詢中直接連接值更好。它自動處理引用和轉義，並且沒有任何HQL注入的風險。