Querying on the base class as opposed to the derived

stathis · **Posted:** Fri Feb 27, 2004 2:24 pm

Hello,

My using Hibernate version 2.0 and mySQL Ver 11.18.

My mapping file it too big to post here, but I think it is not necessary. I have been using a very big hierachy (100+ classes) of joined-subclasses. For simplicity, let's say that the base class is A and Z is one of the derived classes further down the hierarchy (indirectly derived from A).

The query "from Z where id = 10" works fine, but the setting:

Quote:

hibernate.use_outer_join false

is necessary to prevent mySQL from joining more than 31 tables (that's its limit).

I have a situation where I only know the id and not the classname. If I try "from A where id = 10", I get a huge query that (probably) joins all the tables of the database. And i get the following exception:

Quote:

27-Feb-2004 18:18:03 net.sf.hibernate.JDBCException <init>
SEVERE: Could not execute query
java.sql.SQLException: General error, message from server: "Too many tables. MySQL can only use 31 tables in a join"

Is there any setting/solution to allow this kind of query to be broken to smaller queries? I have already set

Quote:

hibernate.dialect net.sf.hibernate.dialect.MySQLDialect

Thanks

meagle · **Joined:** Tue Aug 26, 2003 12:31 pm **Posts:** 14

Right from the FAQ page:

You can set outer-join="false" on associations or, in Hibernate 2.1, use hibernate.max_fetch_depth.

stathis · **Posted:** Mon Mar 01, 2004 3:56 pm

meagle wrote:

Right from the FAQ page:

You can set outer-join="false" on associations or, in Hibernate 2.1, use hibernate.max_fetch_depth.

Well my problem is not associations (which work fine) but deep hierarchy! It seems that hibernate ignores the outer-join false setting for this kind of query. I wonder if it is because of the nature of the query and it can't be executed differently. Does anyone know?