java - Lob 使用 MySQL 和 jpa 返回 null

Question

我正在尝试将文档作为 BLOB 存储在我拥有的 Java 域对象中。

我看过一些帖子说可以使用 @Lob 来完成

http://www.java2s.com/Tutorial/Java/0355__JPA/MarkByteArrayFieldAsLob.htm

所以，我遇到的问题是，当我存储数据时，一切看起来都很好，我可以在我的 mysql 数据库中看到它，但是当我试图在域对象中取出它时，它总是空的。

有什么想法吗？

请注意，我在我的实体中使用的相关 getter 和 setter 如下:

@Lob
public byte[] getData() {
    return data;
}

public void setData(byte[] data) {
    this.data = data;
}

更新 根据 Pascal Thivent 的评论，我添加了一些代码。我还简化了测试。如果我有一个实体对象，有两个字段，一个 id 和数据，例如

@Entity
@Table(name = "picture")
public class Picture extends BaseObject{

    Long id;
    byte[] data;    

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)  
    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }


    @Lob
    public byte[] getData() {
        return data;
    }

    public void setData(byte[] data) {
        this.data = data;
    }
}

现在，我可以毫无问题地创建和保存数据。但是，当我尝试通过调用标准来检索数据时

 this.entityManager.find(clazz, id);

填充了 Picture.class 和相关的 id，我得到以下异常。

请注意异常中的一个非常有趣的行，我认为这是关键:

CausedBy: mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: Unknown column "test@email.com"

请注意，“test@email.com”是我放入数据字段的字节数组的值，所以就好像 sql 正在寻找一个列名，它实际上是字节数组的名称内容。奇怪!

javax.persistence.PersistenceException: org.hibernate.exception.SQLGrammarException: could not load an entity: [com.model.Picture#2]
    at org.hibernate.ejb.AbstractEntityManagerImpl.throwPersistenceException(AbstractEntityManagerImpl.java:630)
    at org.hibernate.ejb.AbstractEntityManagerImpl.find(AbstractEntityManagerImpl.java:195)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.springframework.orm.jpa.SharedEntityManagerCreator$SharedEntityManagerInvocationHandler.invoke(SharedEntityManagerCreator.java:198)
    at $Proxy28.find(Unknown Source)
    at com.service.impl.BaseManagerImpl.get(BaseManagerImpl.java:55)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:307)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:182)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:149)
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:106)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:204)
    at $Proxy32.get(Unknown Source)
    at com.service.UserManagerTest.testSaveOrUpdatePicture(UserManagerTest.java:33)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at junit.framework.TestCase.runTest(TestCase.java:154)
    at junit.framework.TestCase.runBare(TestCase.java:127)
    at junit.framework.TestResult$1.protect(TestResult.java:106)
    at junit.framework.TestResult.runProtected(TestResult.java:124)
    at junit.framework.TestResult.run(TestResult.java:109)
    at junit.framework.TestCase.run(TestCase.java:118)
    at org.eclipse.jdt.internal.junit.runner.junit3.JUnit3TestReference.run(JUnit3TestReference.java:130)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:460)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:673)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:386)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:196)
Caused by: org.hibernate.exception.SQLGrammarException: could not load an entity: [com.model.Picture#2]
    at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:67)
    at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:43)
    at org.hibernate.loader.Loader.loadEntity(Loader.java:1874)
    at org.hibernate.loader.entity.AbstractEntityLoader.load(AbstractEntityLoader.java:48)
    at org.hibernate.loader.entity.AbstractEntityLoader.load(AbstractEntityLoader.java:42)
    at org.hibernate.persister.entity.AbstractEntityPersister.load(AbstractEntityPersister.java:3044)
    at org.hibernate.event.def.DefaultLoadEventListener.loadFromDatasource(DefaultLoadEventListener.java:395)
    at org.hibernate.event.def.DefaultLoadEventListener.doLoad(DefaultLoadEventListener.java:375)
    at org.hibernate.event.def.DefaultLoadEventListener.load(DefaultLoadEventListener.java:139)
    at org.hibernate.event.def.DefaultLoadEventListener.proxyOrLoad(DefaultLoadEventListener.java:195)
    at org.hibernate.event.def.DefaultLoadEventListener.onLoad(DefaultLoadEventListener.java:103)
    at org.hibernate.impl.SessionImpl.fireLoad(SessionImpl.java:878)
    at org.hibernate.impl.SessionImpl.get(SessionImpl.java:815)
    at org.hibernate.impl.SessionImpl.get(SessionImpl.java:808)
    at org.hibernate.ejb.AbstractEntityManagerImpl.find(AbstractEntityManagerImpl.java:175)
    ... 35 more
Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: Unknown column 'test@email.com' in 'field list'
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:406)
    at com.mysql.jdbc.Util.getInstance(Util.java:381)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1031)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:957)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3376)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3308)
    at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1837)
    at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:1961)
    at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2543)
    at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:1737)
    at com.mysql.jdbc.PreparedStatement.executeQuery(PreparedStatement.java:1888)
    at com.mysql.jdbc.BlobFromLocator.length(BlobFromLocator.java:334)
    at org.hibernate.type.ByteArrayBlobType.get(ByteArrayBlobType.java:89)
    at org.hibernate.type.AbstractLobType.nullSafeGet(AbstractLobType.java:46)
    at org.hibernate.type.AbstractType.hydrate(AbstractType.java:81)
    at org.hibernate.persister.entity.AbstractEntityPersister.hydrate(AbstractEntityPersister.java:2096)
    at org.hibernate.loader.Loader.loadFromResultSet(Loader.java:1380)
    at org.hibernate.loader.Loader.instanceNotYetLoaded(Loader.java:1308)
    at org.hibernate.loader.Loader.getRow(Loader.java:1206)
    at org.hibernate.loader.Loader.getRowFromResultSet(Loader.java:580)
    at org.hibernate.loader.Loader.doQuery(Loader.java:701)
    at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:236)
    at org.hibernate.loader.Loader.loadEntity(Loader.java:1860)
    ... 47 more

根据 Pascal 的要求生成的 SQL 是:

Hibernate: select picture0_.id as id32_0_, picture0_.data as data32_0_ from picture picture0_ where picture0_.id=?

Answer 1

尝试为 blob 设置获取类型。 JPA 标准说它应该默认为预先加载，但 Hibernate 过去与规范有一些细微差别，因此您可以尝试以下操作

@Lob
@Basic(fetch = FetchType.EAGER)
public byte[] getData() {
        return data;
}