Design question: Mapping multiple Set of similar objects

npeeters · **Joined:** Fri Dec 30, 2005 5:25 am **Posts:** 13

Hibernate version: 3.0.6
Name and version of the database you are using: MySQL

I have a design best practices questions.

Let's say I have an class that has 3 java.util.Set which I want to map.

Code:

package domain.tool;

import java.util.Set;

public class Tools {
   private Set<BusinessIntelligenceTool> businessIntelligence;
   private Set<MonitoringTool> monitoringTools;
   private Set<BuilderTool> buildTools;
}

All the 3 classes (BusinessIntelligenceTool, MonitoringTool and BuilderToon) extend the same parent class (AbstractTool), and therefore have the same fields (name). Typically, the one-to-many relationship that the collections create would require me to create 3 additonnal tables to store the relationships. I'd like to avoid that.

I'd like to know if it's possible to store all the entries in 1 table. This would for example be the mapping for one of the 3 classes in one of my Sets.
They'd all write to the table "TOOLS" which would be common for the all 3 classes...

Code:

<class name="domain.tool.BusinessIntelligenceTool" table="TOOLS">
    <id name="id" column="ID" type="int">
       <generator class="native"/>
    </id>
    <property name="name" type="string">
       <column name="NAME" not-null="true" index="TOOL_NAME"/>
    </property>

    <property name="fk" type="int">
       <column name="BI_TOOL_ID" />
    </property>
    <many-to-one name="project" class="domain.tool.Tools">
       <column name="TOOLS_ID" not-null="true"/>
    </many-to-one> 
</class>

Is that a good design? Anything else to suggest?
Here are my questions.

- How can I map the 3 collections the better. Do I need to create 3 different tables, or is it possible to merge them into one...
- Wouldn't a kind of many-to-many be more appropriate?

Thanks a lot for your input!

Cheers,

Nicolas

LaLiLuna · **Posted:** Thu Jan 12, 2006 9:27 am

You may consider to use inheritance mapping as explained in the reference. In this case you have the choice to only create one class. The types can be distinguished by a discriminator.

Regards Sebastian

npeeters · **Joined:** Fri Dec 30, 2005 5:25 am **Posts:** 13

Well, I'm afraid my question was not really clear...

The problem is not the mapping of the inheritance (with a discriminator), it's the way that I can map my Collections (the 3 java.util.Set's) which all require a separate table to represent the one-to-many relationship.

(Actually, in my real example, I have 9 sets). This make a lot of unnecessary tables, which I'd like to avoid if it's possible. I'd like to group the information in a main table, especially considering all the objects have a similar type of info (since they inherit from the same parent class).

I have looked in the sample in the Hibernate in Action book and I could not find a good example of that. I realise this is more a general design question than a pure Hibernate API question.

Hope this clears up the confusion.

Thanks!!

Nicolas

LaLiLuna · **Posted:** Thu Jan 12, 2006 5:49 pm

Still look at the inheritance. Table per hierarchy. There is a possibility to have one table with all information in it.

Another idea use composition.
Tool
class Special Tool(
private Tool too;
private Specialtooattribute x;
...

Regards Sebastian