I am trying to learn hibernate, my first application tries to do a 1-to-many, many-to-one mapping (Parent/Child). I have followed all the steps (documentation chapter 16) but i cant get this to work. Im getting first a parent insert (that is ok) but when its turn for childs it makes updates and an exception is thrown obviously. The examples at chapter 16 first saves the parent (i suppose), then loads it (with sess.load) and then inserts the childs,

Can you post your hibernate.config.xml file? It looks like you're missing some settings in there.

######################
### Query Language ###
######################

## define query language constants / function names

hibernate.query.substitutions true 1, false 0, yes 'Y', no 'N'



#################
### Platforms ###
#################

## JNDI Datasource

#hibernate.connection.datasource jdbc/test
#hibernate.connection.username db2
#hibernate.connection.password db2


## HypersonicSQL

#hibernate.dialect net.sf.hibernate.dialect.HSQLDialect
#hibernate.connection.driver_class org.hsqldb.jdbcDriver
#hibernate.connection.username sa
#hibernate.connection.password
#hibernate.connection.url jdbc:hsqldb:hsql://localhost
#hibernate.connection.url jdbc:hsqldb:test
#hibernate.connection.url jdbc:hsqldb:.


## PostgreSQL

#hibernate.dialect net.sf.hibernate.dialect.PostgreSQLDialect
#hibernate.connection.driver_class org.postgresql.Driver
#hibernate.connection.url jdbc:postgresql:template1
#hibernate.connection.username pg
#hibernate.connection.password
#hibernate.query.substitutions yes 'Y', no 'N'


## DB2

#hibernate.dialect net.sf.hibernate.dialect.DB2Dialect
#hibernate.connection.driver_class COM.ibm.db2.jdbc.app.DB2Driver
#hibernate.connection.url jdbc:db2:test
#hibernate.connection.username db2
#hibernate.connection.password db2


## DB2/400

#hibernate.dialect net.sf.hibernate.dialect.DB2400Dialect
#hibernate.connection.username user
#hibernate.connection.password password

## Native driver
#hibernate.connection.driver_class COM.ibm.db2.jdbc.app.DB2Driver
#hibernate.connection.url jdbc:db2://systemname

## Toolbox driver
#hibernate.connection.driver_class com.ibm.as400.access.AS400JDBCDriver
#hibernate.connection.url jdbc:as400://systemname


## MySQL

hibernate.dialect net.sf.hibernate.dialect.MySQLDialect
hibernate.connection.driver_class org.gjt.mm.mysql.Driver
hibernate.connection.driver_class com.mysql.jdbc.Driver
hibernate.connection.url jdbc:mysql://localhost/taller
hibernate.connection.username root
hibernate.connection.password


## Oracle

#hibernate.dialect net.sf.hibernate.dialect.Oracle9Dialect
#hibernate.dialect net.sf.hibernate.dialect.OracleDialect
#hibernate.connection.driver_class oracle.jdbc.driver.OracleDriver
#hibernate.connection.username ora
#hibernate.connection.password ora
#hibernate.connection.url jdbc:oracle:thin:@localhost:1521:test


## Sybase

#hibernate.dialect net.sf.hibernate.dialect.SybaseDialect
#hibernate.connection.driver_class com.sybase.jdbc2.jdbc.SybDriver
#hibernate.connection.username sa
#hibernate.connection.password sasasa
#hibernate.connection.url jdbc:sybase:Tds:co3061835-a:5000/tempdb


## Mckoi SQL

#hibernate.dialect net.sf.hibernate.dialect.MckoiDialect
#hibernate.connection.driver_class com.mckoi.JDBCDriver
#hibernate.connection.url jdbc:mckoi:///
#hibernate.connection.url jdbc:mckoi:local://C:/mckoi1.00/db.conf
#hibernate.connection.username admin
#hibernate.connection.password nimda


## SAP DB

#hibernate.dialect net.sf.hibernate.dialect.SAPDBDialect
#hibernate.connection.driver_class com.sap.dbtech.jdbc.DriverSapDB
#hibernate.connection.url jdbc:sapdb://localhost/TST
#hibernate.connection.username TEST
#hibernate.connection.password TEST
#hibernate.query.substitutions yes 'Y', no 'N'


## MS SQL Server

#hibernate.dialect net.sf.hibernate.dialect.SQLServerDialect
#hibernate.connection.username sa
#hibernate.connection.password sa

## JSQL Driver
#hibernate.connection.driver_class com.jnetdirect.jsql.JSQLDriver
#hibernate.connection.url jdbc:JSQLConnect://1E1/test

## JTURBO Driver
#hibernate.connection.driver_class com.newatlanta.jturbo.driver.Driver
#hibernate.connection.url jdbc:JTurbo://1E1:1433/test

## WebLogic Driver
#hibernate.connection.driver_class weblogic.jdbc.mssqlserver4.Driver
#hibernate.connection.url jdbc:weblogic:mssqlserver4:1E1:1433

## Microsoft Driver (not recommended!)
#hibernate.connection.driver_class com.microsoft.jdbc.sqlserver.SQLServerDriver
#hibernate.connection.url jdbc:microsoft:sqlserver://1E1;DatabaseName=test;SelectMethod=cursor

## jTDS
#hibernate.connection.driver_class net.sourceforge.jtds.jdbc.Driver
#hibernate.connection.url jdbc:jtds:sqlserver://1E1/test;SelectMethod=cursor
#hibernate.jdbc.use_scrollable_resultset false

## Interbase

#hibernate.dialect net.sf.hibernate.dialect.InterbaseDialect
#hibernate.connection.username sysdba
#hibernate.connection.password masterkey

## DO NOT specify hibernate.connection.sqlDialect

## InterClient

#hibernate.connection.driver_class interbase.interclient.Driver
#hibernate.connection.url jdbc:interbase://localhost:3060/C:/firebird/test.gdb

## Pure Java

#hibernate.connection.driver_class org.firebirdsql.jdbc.FBDriver
#hibernate.connection.url jdbc:firebirdsql:localhost/3050:/firebird/test.gdb


## Pointbase

#hibernate.dialect net.sf.hibernate.dialect.PointbaseDialect
#hibernate.connection.driver_class com.pointbase.jdbc.jdbcUniversalDriver
#hibernate.connection.url jdbc:pointbase:embedded:sample
#hibernate.connection.username PBPUBLIC
#hibernate.connection.password PBPUBLIC



#################################
### Hibernate Connection Pool ###
#################################

hibernate.connection.pool_size 1



###########################
### C3P0 Connection Pool###
###########################

#hibernate.c3p0.max_size 2
#hibernate.c3p0.min_size 2
#hibernate.c3p0.timeout 5000
#hibernate.c3p0.max_statements 100
#hibernate.c3p0.idle_test_period 3000
#hibernate.c3p0.acquire_increment 2
##hibernate.c3p0.validate false



###################################
### Apache DBCP Connection Pool ###
###################################

## connection pool

hibernate.dbcp.maxActive 10
hibernate.dbcp.whenExhaustedAction 1
hibernate.dbcp.maxWait 120000
hibernate.dbcp.maxIdle 5

## prepared statement cache

hibernate.dbcp.ps.maxActive 10
hibernate.dbcp.ps.whenExhaustedAction 1
hibernate.dbcp.ps.maxWait 120000
hibernate.dbcp.ps.maxIdle 5

## optional query to validate pooled connections:

#hibernate.dbcp.validationQuery select 1 from dual
#hibernate.dbcp.testOnBorrow true
#hibernate.dbcp.testOnReturn false



##############################
### Proxool Connection Pool###
##############################

## Properties for external configuration of Proxool

hibernate.proxool.pool_alias pool1

## Only need one of the following

#hibernate.proxool.existing_pool true
#hibernate.proxool.xml proxool.xml
#hibernate.proxool.properties proxool.properties



#################################
### Plugin ConnectionProvider ###
#################################

## use a custom ConnectionProvider (if not set, Hibernate will choose a built-in ConnectionProvider using hueristics)

#hibernate.connection.provider_class net.sf.hibernate.connection.DriverManagerConnectionProvider
#hibernate.connection.provider_class net.sf.hibernate.connection.DatasourceConnectionProvider
#hibernate.connection.provider_class net.sf.hibernate.connection.C3P0ConnectionProvider
#hibernate.connection.provider_class net.sf.hibernate.connection.DBCPConnectionProvider
#hibernate.connection.provider_class net.sf.hibernate.connection.ProxoolConnectionProvider



#######################
### Transaction API ###
#######################

## the Transaction API abstracts application code from the underlying JTA or JDBC transactions

#hibernate.transaction.factory_class net.sf.hibernate.transaction.JTATransactionFactory
#hibernate.transaction.factory_class net.sf.hibernate.transaction.JDBCTransactionFactory


## to use JTATransactionFactory, Hibernate must be able to locate the UserTransaction in JNDI
## default is java:comp/UserTransaction
## you do NOT need this setting if you specify hibernate.transaction.manager_lookup_class

#jta.UserTransaction jta/usertransaction
#jta.UserTransaction javax.transaction.UserTransaction
#jta.UserTransaction UserTransaction


## to use JCS caching with JTA, Hibernate must be able to obtain the JTA TransactionManager

#hibernate.transaction.manager_lookup_class net.sf.hibernate.transaction.JBossTransactionManagerLookup
#hibernate.transaction.manager_lookup_class net.sf.hibernate.transaction.WeblogicTransactionManagerLookup
#hibernate.transaction.manager_lookup_class net.sf.hibernate.transaction.WebSphereTransactionManagerLookup
#hibernate.transaction.manager_lookup_class net.sf.hibernate.transaction.OrionTransactionManagerLookup
#hibernate.transaction.manager_lookup_class net.sf.hibernate.transaction.ResinTransactionManagerLookup



##############################
### Miscellaneous Settings ###
##############################

## print all generated SQL to the console

hibernate.show_sql true


## auto schema export

#hibernate.hbm2ddl.auto create-drop
#hibernate.hbm2ddl.auto create
#hibernate.hbm2ddl.auto update


## specify a JDBC isolation level

#hibernate.connection.isolation 4


## set the JDBC fetch size

#hibernate.jdbc.fetch_size 25


## set the maximum JDBC 2 batch size (a nonzero value enables batching)

hibernate.jdbc.batch_size 0


## enable use of JDBC 2 scrollable ResultSets (specifying a Dialect will cause Hibernate to use a sensible default)

#hibernate.jdbc.use_scrollable_resultset true


## use streams when writing binary types to / from JDBC

hibernate.jdbc.use_streams_for_binary true


## use JDBC 3 PreparedStatement.getGeneratedKeys to get the identifier of an inserted row

#hibernate.jdbc.use_get_generated_keys true


## specify a default schema for unqualified tablenames

#hibernate.default_schema test


## use a custom stylesheet for XML generation (if not specified, hibernate-default.xslt will be used)

#hibernate.xml.output_stylesheet C:/Hibernate/net/sf/hibernate/hibernate-default.xslt


## enable outerjoin fetching (specifying a Dialect will cause Hibernate to use sensible default)

#hibernate.use_outer_join false


## set the maximum depth of the outer join fetch tree

hibernate.max_fetch_depth 1


## enable CGLIB reflection optimizer (enabled by default)

#hibernate.cglib.use_reflection_optimizer false



##########################
### Second-level Cache ###
##########################

## optimize chache for minimal "puts" instead of minimal "gets" (good for clustered cache)

#hibernate.cache.use_minimal_puts true


## set a prefix for cache region names

hibernate.cache.region_prefix hibernate.test


## enable the query cache

hibernate.cache.use_query_cache true


## choose a cache implementation

hibernate.cache.provider_class net.sf.ehcache.hibernate.Provider
#hibernate.cache.provider_class net.sf.hibernate.cache.EmptyCacheProvider
#hibernate.cache.provider_class net.sf.hibernate.cache.HashtableCacheProvider
#hibernate.cache.provider_class net.sf.hibernate.cache.TreeCacheProvider
#hibernate.cache.provider_class net.sf.hibernate.cache.OSCacheProvider
#hibernate.cache.provider_class net.sf.hibernate.cache.JCSCacheProvider
#hibernate.cache.provider_class net.sf.hibernate.cache.SwarmCacheProvider



############
### JNDI ###
############

## specify a JNDI name for the SessionFactory

#hibernate.session_factory_name hibernate/session_factory


## Hibernate uses JNDI to bind a name to a SessionFactory and to look up the JTA UserTransaction;
## if hibernate.jndi.* are not specified, Hibernate will use the default InitialContext() which
## is the best approach in an application server

#file system
#hibernate.jndi.class com.sun.jndi.fscontext.RefFSContextFactory
#hibernate.jndi.url file:/

#WebSphere
#hibernate.jndi.class com.ibm.websphere.naming.WsnInitialContextFactory
#hibernate.jndi.url iiop://localhost:900/

Im using hibernate 2.1, mysql 4.0.20a, java 1.4.2 and eclipse

It will be nice if we could just add childs to parents collection and then insert the parent and all stuff goes inserted but, reading the faq i saw
[b]Batch update row count wrong / SQL update or deletion failed (row not found) [/b] that says that i need first insert (save) the parent, then add childs to parent and finally save all childs individually, its that right? Let me read again the reference.

<hibernate-mapping>

<class name="eg.Parent" table="parent">

<id name="id">
<generator class="native"/>
</id>

<set name="children">
<key column="parent_id"/>
<one-to-many class="eg.Child"/>
</set>

</class>

</hibernate-mapping>

then something like:

Parent p = session.load(Parent.class, new Integer(1)); // parent already exists
Set s = p.getChildren();
Child c = new Child();
s.add(c);
//session.save(c);
session.save(p);

Will fail! You must save the child first (by uncommenting the commented-out line) even though--at the time of saving--it has no parent_id!

nope.

this should work the way you have it, except

instead of
session.save(p);

you need
session.flush ();

hibernate is smart enoguh to find all the dirty stuff in its session.

I tried with session.flush and still not working. What im doing wrong? Im tired, please help

You will need to set cascade="save-update" (at least) to get the effect that you're trying to achieve (i.e., saving parent and cascading children). Also, to persist the parent and have the children save as well: save, flush, and then if you are not in a transaction do a session.connection().commit();.

HTH,
Lou