[英]Hibernate does not initialize many-to-one relation after merge
I have the following class: 我有以下课程:
public class Entry{
private long cardNumber;
private long companyId;
private Company company;
private Long id;
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public long getCardNumber() {
return mediaSerialNumberId;
}
public void setCardNumber(long number) {
this.cardNumber = number;
}
public long getCompanyId() {
return companyId;
}
public void setCompanyId(long id) {
this.companyId = id;
}
public Company getCompany() {
return company;
}
public void setCompany(Company company) {
this.company = company;
}
}
With the following uni-directional mapping to a Company: 通过以下单向映射到公司:
<hibernate-mapping>
<class name="foo.bar.Entry" table="RECONSTRUCTION" polymorphism="implicit" lazy="false">
<id name="id" column="ID" type="long" unsaved-value="null">
<generator class="sequence">
<param name="sequence">SEQ_ENTRY</param>
</generator>
</id>
<property name="cardNumber" column="CARDNUMBER" type="long"/>
<property name="companyId" column="COMPANYID" type="long"/>
<many-to-one name="company" column="COMPANYID" class="foo.bar.Company" insert="false" update="false" />
</class>
</hibernate-mapping>
I create a new Entry,set CardNumber=123, CompanyId=3 and and save it with session.merge(). 我创建一个新条目,设置CardNumber = 123,CompanyId = 3并使用session.merge()保存。 The Company with ID=3 exists, I can load it with session.load(). ID = 3的公司存在,我可以用session.load()加载它。 The Company does not have any Hibernate-relation back to Entry. 公司没有任何与休眠有关的回溯关系。
The returned persisted Entry has getCompanyId()==3 but getCompany()==null. 返回的持久条目具有getCompanyId()== 3,但getCompany()== null。
Why isn't the many-to-one relation initialized by Hibernate in the newly persisted object? 为什么Hibernate不在新持久化的对象中初始化多对一关系? If I switch so that the "companyId" attribute is insert/update=false, I can set an existing Company object instead, but then the getCompanyId()==null instead of the ID of the Company. 如果切换为使“ companyId”属性为insert / update = false,则可以设置现有的Company对象,但是可以设置getCompanyId()== null而不是Company的ID。
In the database the COMPANYID column is correctly saved. 在数据库中,正确保存了COMPANYID列。
I am using Hibernate 3.6.10. 我正在使用Hibernate 3.6.10。
You need to refresh
the entity: 您需要refresh
实体:
Entry entry = new Entry();
entry.setCardNumber(123);
entry.setCompanyId(3);
entry = session.merge(entry);
session.flush();
session.refresh(entry );
Because the merge copies the given entity state over the one fetched from the database, the null many-to-one association will also be copied over the one fetched from the database. 由于合并将给定实体状态复制到从数据库获取的状态上,因此空多对一关联也将复制到从数据库获取的状态。 A refresh
should solve it. refresh
应该可以解决它。
A better approach is to simply use the many-to-one association without the extra companyId
column: 更好的方法是简单地使用多对一关联,而无需额外的companyId
列:
<many-to-one name="company" column="COMPANYID" class="foo.bar.Company"/>
This way, you can even set the company without having to fetch it from DB: 这样,您甚至可以设置公司,而不必从数据库获取它:
Entry entry = new Entry();
entry.setCardNumber(123);
entry.setCompany(new Company());
entry.getCompany().setId(3);
session.persist(session);
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