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java - 如何在JPA中正确保持多对多关系

我有两个与多对多相关的简单表file和row。一个文件可以包含多行，而一行可以包含在多个文件中。

CREATE TABLE file
(
  id INT(11) PRIMARY KEY NOT NULL AUTO_INCREMENT,
  name VARCHAR(30) DEFAULT '' NOT NULL
);
CREATE UNIQUE INDEX file_id_uindex ON file (id);

CREATE TABLE row
(
    id BINARY(16) PRIMARY KEY NOT NULL,
    content TEXT
);
CREATE UNIQUE INDEX row_id_uindex ON row (id);

CREATE TABLE file_row
(
    file_id INT(11),
    row_id BINARY(16),
    CONSTRAINT file_id___fk FOREIGN KEY (file_id) REFERENCES file (id),
    CONSTRAINT row_id___fk FOREIGN KEY (row_id) REFERENCES row (id)
);
CREATE INDEX file_id___fk ON file_row (file_id);
CREATE INDEX row_id___fk ON file_row (row_id);


由于row.id我使用行内容的哈希，因此在表中只能存储唯一的行。

还有我在java中的映射类：

@Getter
@Setter
@Entity
@Table(name = "file")
public class File implements Serializable {

    @Builder
    public File(int id, String name, List<Row> rows) {
        this.id = id;
        this.name =name;
        this.rows = rows;
    }

    public File(){
    }

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    @Column(name = "name")
    private String name;

    @ManyToMany(cascade = CascadeType.MERGE)
    @JoinTable(name = "file_row",
            joinColumns = @JoinColumn(name = "file_id"),
            inverseJoinColumns = @JoinColumn(name = "row_id"))
    private List<Row> rows;
}

@Getter
@Setter
@Entity
@Table(name = "row")
public class Row implements Serializable{

    public Row() {
    }

    @Builder
    public Row(byte[] id, String content, List<File> files){
        this.id = id;
        this.content = content;
        this.files = files;
    }

    @Id
    @Column(columnDefinition = "BINARY(16)")
    private byte[] id;

    @Lob
    @Column(name = "content")
    private String content;

    @ManyToMany(mappedBy = "rows", cascade = CascadeType.MERGE)
    private List<File> files;
}


为了保存实体，我使用persist()类的EntityManager方法。

当我添加具有唯一行的新文件时-一切都很好。但是，如果我尝试保留重复行的文件，则会发生错误：

Caused by: javax.persistence.EntityExistsException: A different object with the same identifier value was already associated with the session : [com.restapp.entity.Row#[B@183c1f56]
    at org.hibernate.jpa.spi.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1664)
    at org.hibernate.jpa.spi.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1602)
    at org.hibernate.jpa.spi.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1608)
    at org.hibernate.jpa.spi.AbstractEntityManagerImpl.persist(AbstractEntityManagerImpl.java:1152)
    at org.jboss.as.jpa.container.AbstractEntityManager.persist(AbstractEntityManager.java:580)
    at com.restapp.dao.AbstractDao.persist(AbstractDao.java:43)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.jboss.as.ee.component.ManagedReferenceMethodInterceptor.processInvocation(ManagedReferenceMethodInterceptor.java:52)
    at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:340)
    at org.jboss.invocation.InterceptorContext$Invocation.proceed(InterceptorContext.java:437)
    at org.jboss.as.weld.ejb.Jsr299BindingsInterceptor.doMethodInterception(Jsr299BindingsInterceptor.java:82)
    at org.jboss.as.weld.ejb.Jsr299BindingsInterceptor.processInvocation(Jsr299BindingsInterceptor.java:93)
    at org.jboss.as.ee.component.interceptors.UserInterceptorFactory$1.processInvocation(UserInterceptorFactory.java:63)
    at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:340)
    at org.jboss.as.ejb3.component.invocationmetrics.ExecutionTimeInterceptor.processInvocation(ExecutionTimeInterceptor.java:43)
    at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:340)
    at org.jboss.as.jpa.interceptor.SBInvocationInterceptor.processInvocation(SBInvocationInterceptor.java:47)
    at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:340)
    at org.jboss.invocation.InterceptorContext$Invocation.proceed(InterceptorContext.java:437)
    at org.jboss.weld.ejb.AbstractEJBRequestScopeActivationInterceptor.aroundInvoke(AbstractEJBRequestScopeActivationInterceptor.java:64)
    at org.jboss.as.weld.ejb.EjbRequestScopeActivationInterceptor.processInvocation(EjbRequestScopeActivationInterceptor.java:83)
    at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:340)
    at org.jboss.as.ee.concurrent.ConcurrentContextInterceptor.processInvocation(ConcurrentContextInterceptor.java:45)
    at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:340)
    at org.jboss.invocation.InitialInterceptor.processInvocation(InitialInterceptor.java:21)
    at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:340)
    at org.jboss.invocation.ChainedInterceptor.processInvocation(ChainedInterceptor.java:61)
    at org.jboss.as.ee.component.interceptors.ComponentDispatcherInterceptor.processInvocation(ComponentDispatcherInterceptor.java:52)
    at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:340)
    at org.jboss.as.ejb3.component.pool.PooledInstanceInterceptor.processInvocation(PooledInstanceInterceptor.java:51)
    at org.jboss.invocation.InterceptorContext.proceed(InterceptorContext.java:340)
    at org.jboss.as.ejb3.tx.CMTTxInterceptor.invokeInCallerTx(CMTTxInterceptor.java:254)
    ... 178 more


当我使用表中已经存在的行持久存储文件时，也会发生错误。

Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Duplicate entry '\xE6t\xDB]\xFA\xF0\xAFz\xD4\xED\xAE\xFC\x84\xD7\x99\xA9' for key 'PRIMARY'
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:425)
    at com.mysql.jdbc.Util.getInstance(Util.java:408)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:935)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3970)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3906)
    at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2524)
    at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2677)
    at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2549)
    at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:1861)
    at com.mysql.jdbc.PreparedStatement.executeUpdateInternal(PreparedStatement.java:2073)
    at com.mysql.jdbc.PreparedStatement.executeUpdateInternal(PreparedStatement.java:2009)
    at com.mysql.jdbc.PreparedStatement.executeLargeUpdate(PreparedStatement.java:5098)
    at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:1994)
    at org.jboss.jca.adapters.jdbc.WrappedPreparedStatement.executeUpdate(WrappedPreparedStatement.java:537)
    at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.executeUpdate(ResultSetReturnImpl.java:204)
    ... 129 more


请帮我解决我的问题。

最佳答案

所以，看来我找到了解决方案。那就是我所做的：


使用merge()类的EntityManager方法而不是persist()添加新文件（link）。
将<property name="hibernate.event.merge.entity_copy_observer" value="allow"/>添加到persistence.xml属性（link）。

关于java - 如何在JPA中正确保持多对多关系，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/39949492/

10-12 22:31
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