java 休眠：无法在类上找到合适的构造函数
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hibernate: Unable to locate appropriate constructor on class
提问by Frazer
Here is my class:
这是我的课：
public class TrainLate {
private int id;
private Date startDate;
private Date endDate;
private Set<TrainSchedule> ts=new HashSet<TrainSchedule>();
public TrainLate(){}
public TrainLate(int id, Date startDate, Date endDate) {
super();
this.id = id;
this.startDate = startDate;
this.endDate = endDate;
}
// setters and getters...
}
The type Date is java.sql.Date
日期类型是 java.sql.Date
In another class I use HQL:
在另一堂课中，我使用 HQL：
String hql="SELECT new TrainLate(id,startDate,endDate) FROM TrainLate "+ "WHERE id="+String.valueOf(index);
where index is an int parameter.
其中 index 是一个 int 参数。
Here is the "TrainLate.hbm.xml":
这是“TrainLate.hbm.xml”：
<class name="classes.TrainLate">
<id name="id">
<generator class="native"/>
</id>
<property name="startDate"/>
<property name="endDate"/>
<set name="ts" lazy="false" cascade="all-delete-orphan" inverse="true">
<key column="trainLateID" />
<one-to-many class="classes.TrainSchedule" />
</set>
</class>
Here is the exception:
这是例外：
Unable to locate appropriate constructor on class [classes.TrainLate] [SELECT new TrainLate(id,startDate,endDate) FROM classes.TrainLate WHERE id=0]
Where "classes" is the package name.
其中“classes”是包名。
回答by dcernahoschi
First: Hibernate requires your entities to have a default no argument constructor.
第一：Hibernate 要求您的实体具有默认的无参数构造函数。
Second: Your hql should be: "from TrainLate t where t.id = :id".
第二：你的 hql 应该是："from TrainLate t where t.id = :id"。
String hql = "from TrainLate t where t.id = :id";
List<TrainLate> result = (List<TrainLate>) session.createQuery(hql).setParameter("id", 1).list();
Or even better. When you know the id of the entity you don't need to search with hql:
或者甚至更好。当您知道实体的 id 时，您无需使用 hql 进行搜索：
TrainLate t = session.get(TrainLate.class, 1L); // I assume your id is a Long
This one returns nullif the entity is not found.
null如果未找到实体，则返回此值。
or
或者
TrainLate t = session.load(TrainLate.class, 1L); // I assume your id is a Long
This one throws an ObjectNotFoundExceptionif the entity is not found.
ObjectNotFoundException如果未找到实体，则抛出一个。
回答by Mark Bramnik
I know it can sound silly, but have you tried to debug this thing?
我知道这听起来很傻，但你有没有试过调试这个东西？
My first thought would be (if I were hibernate :) ) to create an object of TrainLate with No-OP constructor and then invoke a series of setters to set id, startDate and endDate.
我的第一个想法是（如果我处于休眠状态:)）使用 No-OP 构造函数创建一个 TrainLate 对象，然后调用一系列 setter 来设置 id、startDate 和 endDate。
I didn't see it in your code snippet...
我在你的代码片段中没有看到它......
