Hello all,

I am new in hibernate and have simple question.

I have the following data model.

class Address {
int id;
Country country;
}

class Country {
int id;
String name;
}

.hbm is the following :

<class name="Country" table="Countries">
<id name="id" column="id" unsaved-value="null">
<generator class="increment"/>
</id>
<property name="name" column="name" not-null="true"/>
</class>

<class name="Address" table="Addresses">
<id name="id" column="id" unsaved-value="null">
<generator class="increment"/>
</id>
<one-to-one name="country" class="Country"/>
</class>

I load this class from database. All is OK. Then I try to modify address.
I set new country but do not change country filed just country.id. Then
I try to save modified object. There are not exceptions but my changes are not saved and just ignored.

..
int id = 1;
Address address = getAddress(id);
System.out.println(address.country.id); // pring "1"
System.out.println(address.country.name); //print "USA"
address.country.id = 2;
save(address);
...
address = getAddress(id);
System.out.println(address.country.id); // pring "1"
System.out.println(address.country.name); //print "USA"
...

I really do not want to do something like this to solve this problem :
...
Address address = getAddress(id);
address.country = getCountry(2);
save(address);
...

Could you please help me? Is is possible to automatically change country.name filed if country.id is changed?

Thanks,
Aritomo

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Read this: http://hibernate.org/42.html

see hibernate manual:

http://www.hibernate.org/hib_docs/refer ... d-cascades

this will enable you to:



you may try to set hibernate to show sql queries (again, see manual), to see what is going on behind the scenes.

imho it is very strange to do:

a.country.id = <something>

you need to set the refernce of object a to reference another object c -- the most obvious way is to use (if you do not want getters/setters) a.country = c;

doing a.country.id = 2 means you are trying to change the primary key of the existing object a.country, you _do_not_ change the reference of a to another object.

Thanks a lot.

Now I modify reference as you proposed.

<class name="Country" table="Countries">
<id name="id" column="id" unsaved-value="null">
<generator class="increment"/>
</id>
<property name="name" column="name" not-null="true"/>
</class>

<class name="Address" table="Addresses">
<id name="id" column="id" unsaved-value="null">
<generator class="increment"/>
</id>
<one-to-one name="country" class="Country" cascade="all"/>
</class>

But changes does not affect address.

id = 1;
Address address = getAddress(id);
address.country = getCountry(2);
save(address);
address = getAddress(id);
System.out.println(address.country.id); // pring "1"
System.out.println(address.country.name); //print "USA"

Could you please help me?

Thanks,
Aritomo

please, enable query logging, for example if you are using hibernate.xml config, add the following (for properties file just use the property names as keys, keep the values the same:





and set the output here, you should see the queries to be executed.[/code]

Log is the following :
update Addresses set StreetNumber=? where id=?
update Countries set name=? where id=?

StreetNumber is just string field. But why country field is not updated?

Thanks,
Aritomo

This code will update the country the address object is associated with, but it will not effect the country itself, only the country the address instance is associated with.

I am sorry. But I still have problem.

Let's me explain :

I have Countries table

table Countries {
int id;
int name;
}

that has e.g. two entries
Countries.id = 1
Countries.name = 'USA'

Countries.id = 2
Countries.name = 'Japan'

Also I have Addresses table :

table Addresses {
int id;
int countryId;
}


Also I have JavaBeans

class Country {
int id;
String name;
}

class Address {
int id;
Country country;
}

I develop .hbm :

<hibernate-mapping>
<class name="Country" table="Countries">
<id name="id" column="id" unsaved-value="null">
<generator class="increment"/>
</id>
<property name="name" column="name" not-null="true"/>
</class>
<class name="Address" table="Addresses">
<id name="id" column="id" unsaved-value="null">
<generator class="increment"/>
</id>
<???-to-??? name="country" class="Country" column="countryId" />
</many-to-one>
</class>
</hibernate-mapping>

Which association should I use here? many-to-one or one-to-one or something else ?

Could you please give me example?

Also I have the following data in Addresses table
Addresses.id = 1
Addresses.countryId=1

Addresses.id = 2
Addresses.countryId=2

Addresses.id = 1
Addresses.countryId=2

Thanks,
Aritomo

for simple reference, use many-to-one from child to parent.

i guess there is only one USA and Japan, but there is several addresses in either country.

you want just one country for every country in the world. you want several addresses in each country.

so:

Address: Washington, ... -> Country USA
Address: New Jersey, ... -> Country USA
Address: Tokyo, ... -> Japan

so use many-to-one in Address.hbm.xml

But this problem have very little common with hibernate -- this is more of a database design, you should read something about SQL databases.

Thanks a lot for help,

Now I use many-to-one :

<hibernate-mapping>
<class name="Country" table="Countries">
<id name="id" column="id" unsaved-value="null">
<generator class="increment"/>
</id>
<property name="name" column="name" not-null="true"/>
</class>
<class name="Address" table="Addresses">
<id name="id" column="id" unsaved-value="null">
<generator class="increment"/>
</id>
<many-to-one name="country" class="Country" column="countryId" />
</many-to-one>
</class>
</hibernate-mapping>

countryId is loaded successfully but name of country is null (Country.name) .
I thinked that name should be loaded automatically? Am I mistaken? Where is error?

Please help.

Thanks,
Aritomo

i guess, you should use getters and setters. ie country.getName() instead of simple country.name

1. by default (your hbm does not specify otherwise) you have always have proxies for associations (like Address -> Country) (ie. properties are null)

2. by default (your hbm does not specify otherwise) as default access method there is a getters/setters, no direct access (ie. the proxy loads the object state (attributes) ones you call a getter/setter)

You hav etoo options:

1. (preferred) define getters/setters

2. define another access method ('field') -- see http://www.hibernate.org/hib_docs/refer ... eclaration and search for "access"