两个实体之间的JPA OneToOne和ManyToMany [英] JPA OneToOne and ManyToMany between two entities
问题描述
我之前问了一个问题,但是我觉得还不够清楚,我会详细说明代码。
我有教师实体和部门实体
许多教师属于一个部门,而b $ b b一个部门有一名教师负责该部门。
以下是我的实施方式。
I asked a question earlier, but think it wasn't clear enough i will elaborate further with the code.
I have a Teacher entity and Department entity
Many Teachers belongs to One Department and
One Department has One Teacher who heads the Department.
Here is how I am implementing it.
@Entity
public class Teacher extends Model {
@Required
public String surname;
@Required
public String othernames;
...
@OneToOne(mappedBy = "deptHead")
public Department headedBy = new Department();
@ManyToOne(cascade=CascadeType.ALL)
public Department dept = new Department();
...
}
和部门实体
@Entity
public class Department extends Model {
@Required
public String deptName;
@OneToMany(mappedBy="dept")
public List<Teacher> teachers = new ArrayList<Teacher>();
@OneToOne
public Teacher deptHead = new Teacher();
...
}
I我收到以下错误
@6c4nj8nmg
Internal Server Error (500) for request GET /
JPA error
A JPA error occurred (Unable to build EntityManagerFactory): could not instantiate test objectmodels.Department
play.exceptions.JPAException: Unable to build EntityManagerFactory
at play.db.jpa.JPAPlugin.onApplicationStart(JPAPlugin.java:269)
at play.plugins.PluginCollection.onApplicationStart(PluginCollection.java:525)
at play.Play.start(Play.java:526)
at play.Play.detectChanges(Play.java:630)
at play.Invoker$Invocation.init(Invoker.java:198)
at Invocation.HTTP Request(Play!)
Caused by: org.hibernate.InstantiationException: could not instantiate test objectmodels.Department
at org.hibernate.engine.UnsavedValueFactory.instantiate(UnsavedValueFactory.java:48)
at org.hibernate.engine.UnsavedValueFactory.getUnsavedIdentifierValue(UnsavedValueFactory.java:67)
at org.hibernate.tuple.PropertyFactory.buildIdentifierProperty(PropertyFactory.java:67)
at org.hibernate.tuple.entity.EntityMetamodel.<init>(EntityMetamodel.java:135)
at org.hibernate.persister.entity.AbstractEntityPersister.<init>(AbstractEntityPersister.java:485)
at org.hibernate.persister.entity.SingleTableEntityPersister.<init>(SingleTableEntityPersister.java:133)
at org.hibernate.persister.PersisterFactory.createClassPersister(PersisterFactory.java:84)
at org.hibernate.impl.SessionFactoryImpl.<init>(SessionFactoryImpl.java:286)
at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1872)
at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:906)
at play.db.jpa.JPAPlugin.onApplicationStart(JPAPlugin.java:267)
... 5 more
Caused by: java.lang.reflect.InvocationTargetException
at org.hibernate.engine.UnsavedValueFactory.instantiate(UnsavedValueFactory.java:45)
... 15 more
Caused by: java.lang.StackOverflowError
at java.lang.Class.searchMethods(Unknown Source)
at java.lang.Class.getMethod0(Unknown Source)
at java.lang.Class.getMethod(Unknown Source)
at play.classloading.enhancers.PropertiesEnhancer$FieldAccessor.invokeWriteProperty(PropertiesEnhancer.java:268)
at models.Department.<init>(Department.java:23)
at models.Teacher.<init>(Teacher.java:47)
at models.Department.<init>(Department.java:26)
...
这些需要帮助
推荐答案
这是不是JPA问题,而是由递归实例化教师
/ 部门
引起的。
This is not a JPA problem, but is caused by recursive instantiation of Teacher
/Department
.
当您创建或要求JPA创建实例时如果教师
,教师
尝试实例化部门
,实例化一个教师
...,到无穷大。
When you create, or ask JPA to create, an instance of Teacher
, the Teacher
attempts to instantiate a Department
, which instantiates a Teacher
..., to infinity.
因此你看到 StackOverflowError
错误接近堆栈跟踪结束。
Hence you're seeing a StackOverflowError
error near the end of that stack trace.
删除 = new Teacher()
和 =来自类定义的新Department()
表达式;在创建它们时依赖并使用适当的setter方法。
Remove the = new Teacher()
and = new Department()
expressions from the class definition; depend on and use appropriate setter methods when you create them.
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