Eclipselink Oracle Lob

You always need special care to read/write lobs not only with JPA but also with JDBC.

In case of JPA you can have persistent lob fields e.g.

 @Lob

@Basic(fetch = FetchType.LAZY)

@Column(nullable = false)

private byte[] content;

Lazy fetch type is usually good, so that not to read lob unless it is required. 

If your entity is detached (almost always in j2ee/web) you have to query for the lob field

SELECT o.content FROM Message o where o.id  = ?

Query.getSingleResult()

In case of Oracle, correct way to read/write lobs varies with db version and driver version. Lobs of size less than 4K are handled normally but for larger sizes it can be an issue. In case of EclipseLink, you just need to set following properties in persistence.xml to read/write lobs > 4K. Behind the screen EclipseLink will first insert empty blob field and then update it to actual value.

<property name="eclipselink.target-database" value=" org.eclipse.persistence.platform.database.oracle.OraclePlatform "/>

<property name="eclipselink.target-server" value="WebLogic_10" />

Assuming you are using Weblogic 10g or higher, for other values refer to Eclipselink docs.


You can verify size of lob fields by following SQL query
select DBMS_LOB.GETLENGTH(content) from message where id = 3