Understanding array serialization

orest.kozyar · **Joined:** Fri Jun 29, 2007 10:12 am **Posts:** 3

I use Hibernate to persist some of my Java classes to a database. Often I will write scripts in other programs (such as Python) to do some analysis on the persisted data. However, some of these classes have arrays of primitive types (such as Integer[][]) which appear to be persisted as a byte stream to the database. I'd like to figure out how to interpret this byte stream using another language, but am having difficulty finding information on the internet. I am not sure whether this is a Hibernate-specific issue or a Java issue and was hoping someone could point me in the right direction.

johnpeeb · **Joined:** Tue Jun 26, 2007 3:24 pm **Posts:** 11

Could you post your mapping file so we can see exactly how you are persisting it? By the way, Integer is a class which wraps the primitive type int.

orest.kozyar · **Joined:** Fri Jun 29, 2007 10:12 am **Posts:** 3

I'm using Hibernate Annotations, so the entity is marked as followed:

@Entity
public class Waveform implements Serializable {

@Id
private Long id;

Double[][] rawWaveform;
Double stimulusDuration;
Integer stimulusLevel;

<-- constructor and methods go here -->

Is this the information that you needed? I can provide the entire class file if necessary.

Thanks!

johnpeeb · **Joined:** Tue Jun 26, 2007 3:24 pm **Posts:** 11

I'm not familiar with hibernate annotations, but I'm sure someone else will be able to help.

venkman · **Joined:** Wed May 28, 2008 11:11 am **Posts:** 12

So you are mapping a member variable of type Double[][] to some column in the database, using annotations? Does it work? How do you do that?

I am interested in knowing how to map a variable of type double[] to a database column of the same type (PostgreSQL). Any ideas?

Thanks, venkman

Cameron McKenzie · **Posted:** Mon Jun 09, 2008 9:40 am

Quote:

Of course, if you've worked with any of the big databases, you're probably familiar with Blobs and Clobs. There is no Blob or Clob annotation to speak of in Hibernate; instead, when Hibernate sees the @Lob annotation, it inspects the Java datatype. If the Java datatype that is decorated with the @Lob annotation is a String, java.sql.Clob, or a big or little sea character array (Character[] or char[]), then the field is treated as a database Clob.

On the other hand, if the Java datatype is a java.sql.Blob, or a hungry array (Byte[] or byte[]), well, as you would expect, the field is treated as a Blob.

http://jpa.ezhibernate.com/Javacode/learn.jsp?tutorial=06hibernatetableandcolumnmappingwithjpa

Well, Hiberante put that blob in there. If you use Hibernate to pull it out, you won't have any problems.

What does the data stream actually look like in the database? Is it totally indecipherable? My guess is that it is, in which case, it'd probably take a pretty smart query to pull it out and put it back into a workable format that you could effectively manipulate in a Java/J2EE application.