More Hibernate glitches, part 2

I had previously written on an Expected positional parameter glitch in Hibernate when joining between entities using OneToOne and PrimaryKey + ForeignKey columns. It turns out, Hibernate has this problem no matter what field you query on the joined entity if you're quering by another entity. A way around this is to use the ID property of the joined entities and add another association to your HQL / Criteria query.

ie So if you have Person and Address having a OneToOne relationship

public class Person {
  @OneToOne
  private Address address;
}

... and you want to query for a Person by Address, you would probably write something like :

from Person p where p.address = ?

... in HQL. Well, this is where you start running into the Expected positional parameter glitch. Instead, write your query like this :

from Person p where p.address.id = ?

... and pass in a long / int / whatever type you use for an identifier for Person / Address instead and this will work around the glitch until it can be fixed.

More Hibernate glitches

I've recently discovered the joy of actually getting OneToOne primary key columns on objects working, so I've started using them more often (where appropriate). Naturally, increased use means increased chances of finding a bug, which I have. It seems there's a parser problem in HQL when it comes to querying on ID columns that are also objects. If you try to query on the object type (ie Person) rather than the ID type (ie Long), you'll get an exception saying something along the lines of :

Expected positional parameter count: 1, actual parameters: [Parent@bec357b] [from Child this where this.id.parent = ?]

The above line is from HHH-2254, but it's representative of the problem I ran across. The problem is that hibernate doesn't properly parse and fill in the parameters in the query. You can get around this by changing the query to use a simple type for ID instead of the object type.

Allowing external root access to your MySQL database

...is recommended against in the MySQL documentation, but it can be oh so handy for running scripts and adding databases, tables and views when you can't (or don't want to) log into that remote system on the command line to update it. However, when you try it (at least on a fresh Ubuntu install), you may be greeted with an Error 2003. This happens when your system does not allow root external access. To enable external access, you can run this query (as root) on your server from the command line (must be localhost) :

GRANT ALL PRIVILEGES ON *.* TO 'root'@'%' IDENTIFIED BY ('myrootpassword');

* EDIT * : The above statement does not necessarily copy all privileges over to the new entry for 'root'@'%' in the mysql.user table. A better way to accomplish full external root access is the following :

DELETE FROM `mysql`.`user` WHERE User = 'root' AND Host = '%';
INSERT INTO `mysql`.`user` (Host, User, Password, Select_priv, Insert_priv, Update_priv, Delete_priv, Create_priv, Drop_priv, Reload_priv, Shutdown_priv, Process_priv, File_priv, Grant_priv, References_priv, Index_priv, Alter_priv, Show_db_priv, Super_priv, Create_tmp_table_priv, Lock_tables_priv, Execute_priv, Repl_slave_priv, Repl_client_priv, Create_view_priv, Show_view_priv, Create_routine_priv, Alter_routine_priv, Create_user_priv, ssl_type, ssl_cipher, x509_issuer, x509_subject, max_questions, max_updates, max_connections, max_user_connections) (SELECT '%', User, Password, Select_priv, Insert_priv, Update_priv, Delete_priv, Create_priv, Drop_priv, Reload_priv, Shutdown_priv, Process_priv, File_priv, Grant_priv, References_priv, Index_priv, Alter_priv, Show_db_priv, Super_priv, Create_tmp_table_priv, Lock_tables_priv, Execute_priv, Repl_slave_priv, Repl_client_priv, Create_view_priv, Show_view_priv, Create_routine_priv, Alter_routine_priv, Create_user_priv, ssl_type, ssl_cipher, x509_issuer, x509_subject, max_questions, max_updates, max_connections, max_user_connections FROM `mysql`.`user` WHERE User = 'root' AND Host = 'localhost');
FLUSH PRIVILEGES;

Spring, Tomcat and memory

As my application has been growing more and more in functionality, it has also been growing in its memory footprint. To that end, I've started getting OutOfMemoryErrors because the heap has started overflowing. That's really not a problem if you have access to the external Tomcat server, you can just increase the heap size using "-Xms128M -Xmx512M" (or other applicable sizes) on the command line, or do this via the GUI if you're running Tomcat in Windows. However, it's not as obvious if you're using Tomcat for debugging within the Web Tools Platform plugins for Eclipse. I started running into this problem recently and it ground my development to a halt until I was able to fix the problem for WTP in Eclipse. WTP passes its arguments to the Tomcat server via the Launch Configuration. To get to it, right click on the Tomcat server in the Servers view -> 'Open' -> 'Open launch configuration' -> 'Arguments' tab -> 'VM arguments:' text box, then add the "-Xms128M -Xmx512M" segment to the end of the parameter list.