Storing empty Strings in Entity with JPA

[Former Member]

Hello Community,

i'm working on a migration of an application to nwds and web-dynpro.

i read data from my old database and want to insert it into the new database.

for that i have two beans, which each using an entity representing the source and the destination data.

when i want to use the persist Method of the Entity-Manager of JPA to persist the data, which was read from the old database, i get some exceptions telling me, that the data of one database-column is an empty string and that jpa cannot assign an empty string.

here some relevant lines of the exceptions:

javax.persistence.PersistenceException: Failed to set value for field >>tabvalue<< of entity >>com.huelsta.kall.entities.RefTable<<.
Exception of type com.sap.sql.log.OpenSQLException caught: Cannot assign an empty string to host variable 4..

But my applications must handle empty strings!!!

Any ideas who to handle that problem are very welcome.

regards

matthias hayk

[Former Member]

Hello,

thanx for your quick answer.

Your recommendation has (unfortunately) another big drawback. My applications uses the Java Dictionary! This is because in that dictionary the can be defined simple-types. this data from that definitions is used in wd-verification-actions and is on the other side a big advance.

But using Java-Dictionary means using the System-Datasource, also means using OpenSQL.

But i simply dont understand the reason of the restrictions.

regards

matthias hayk

[Former Member]

Hello,

of course something like this is possible. i realized this at the moment in such a way using the getter- and setter-methods.

but this should not be!

in all apps in know (including sql itself) it is normal to use empty strings. in sql this would be something like "update table <xyz> set mycolumn='' where id =4711". and an empty string is simply not the same as a null value.

addtionaly i had to find out, that there is also a problem when an string simple ends with blank. so if an objectpropery which is to persist using jpa in sap has the value "abc " an opensql-excetion is raised, telling that the string must not end with a Blank. Even if i could agree to this special issue, i dont aggree in, that it is not possible to persist empfy strings.

any other opinions are welcome

regards

matthias

[Former Member]

Hi Matthias,

Another option is, of course, not to use Open SQL, but Native SQL or Vendor SQL, as the unavailability for empty strings storage is a drawback of the Open SQL only (at least - as far as I know).

More information about using Vendor SQL and Native SQL with JPA: http://help.sap.com/saphelp_nwce10/helpdata/en/2d/23b32e8c0152469edf07909703fe03/frameset.htm

I hope that helps!

Regards,

Yordan

[Former Member]

Hi Matthias,

I am not a Java developer, so I cannot tell you how exactly you can handle this by means of some source code example...

If you first assign a 'null' to the empty string (i.e. check if a string is empty; if so, make it equal to 'null'), and then try to persist it, you should not get those exceptions any more.

I hope that helps!

Regards,

Yordan