I have a many-to-many relationship in the same scenario as the followings:

A person has a set of characters, such as smart, thoughtful, tall, slim, etc.

The character set is not pre-definited in the system. When a user submits a person information, this user must also provide this person's character. If the character description such as "smart" is not in the system (DB), it will be saved into the system. I am not sure how to handle this object creation process with Hibernate in the right way. My thought is to save the character set data first and save the person object. I can think at lease two approachs here. One is to have the unique constraint on the character description and save the character set. This approach might not work with a batch save operation. The second approach I can think of is that to retrieve the character set data from DB first and only save those not in the DB. But, this approach will make the implementation quite complicated.

Any thought in this situation?

Thanks very much for any of your inputs.



Hibernate version: 3.0.x

Mapping documents:

<hibernate-mapping auto-import="true" default-lazy="false">

<class name="com.xyz.myaoo.domain.Person" table="persons">
<id name="id" type="int" unsaved-value="null" >
<generator class="native">
<param name="sequence">persons_id_seq</param>
</generator>
</id>
<set name="charactersInternal" table="personse_characters">
<key column="person_id"/>
<many-to-many column="character_id" class="com.xyz.myapp.domain.Character"/>
</set>
...
</class>
...
</hibernate-mapping>

Code between sessionFactory.openSession() and session.close():

Full stack trace of any exception that occurs:

Name and version of the database you are using:

The generated SQL (show_sql=true):

Debug level Hibernate log excerpt:

Have a look at the docs regarding cascading of associated data. Depending upon the complexity of the associated data (is it really just strings?) and your requirements for how this is used, you might also be able to use a "value collection" as opposed to an "entity collection"

If you just want these properties to be saved as distinct objects each time, make them a collection (probably a list): you'll then have a different row in the table for each "smart" in the system, for each "considerate", etc.

If you want to provide users with a list of all existing person-properties, in the hopes that they won't enter "clever" if "smart" is already in there, then you'll want a many-to-many mapping, with PersonProperty being its own class. You'll need to write business logic to ensure that PersonProperties are looked up before new Persons are saved; if the value isn't in the PersonProperty table then you'll want to add it and put the new object into the Person's list of PersonProperties. This solution ensures that there will only be one "smart" row in the PersonProperty table. Of course, it's up to to ensure that there are no rows like "Smart", "smart ", etc.

Either way, this isn't really a hibernate issue. Deisgn your solution as if you were using plain old JDBC (or even just SQL): whatever your solution, you'll be able to model it using hibernate.

Thanks very much Steve for your information in regarding of "value collection".

After studying the chapter 2.3.4, I modified all related code, mapping files, and DB schema. And my today's test result is good. The "value collection" meets my need. If I only look at the DB table, it is all I need.

Thanks tenwit for your input. I was trying to learn the Hibernate "language" for the case.