hibernate two tables per one entity

Question

I have one entity - User. It is described by User.class.

Hibernate creates one table per entity, so when I call session.save(user), my data is always saved to this table.

Now I need another table for data of same User type, and I need to save my entity to that table only.

Data structure (something like this):

table users_1_table{
  string id;
  string username;
}

table users_2_table{
  string id;
  string username;
}

work with this:

session.save(user1,"users_1_table")
session.save(user2,"users_2_table")

and in result I should have user1 in users_1_table and user2 in users_2_table.

Due to system limitation I can not put these two objects in one table. (Even creating extra field is bad idea).

Can I do this without subclassing? Using programmaticaly hibernate configuration?

Answer 1

Preface:

This is a widely asked question even on SO, and also widely the answers are related to Subclass or actually SuperClass approach (e.g. [1])

Actual answer:

On these posts [2], [3] they suggest to use a xml mapping with EntityName parameter.

So, mapping with xml you don't need superclass, just give the EntityName parameter to two identical mappings.

Example Mapping:

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
   <class name="DomainModel.User, DomainModel"
     table="User1Object" entity-name="User1Object">  
         <id name="_id" access="field" column="id">
             <generator class="assigned"/>
         </id>
        <property name= ...>
 </class>
 <class name="DomainModel.User, DomainModel"
     table="User2Object" entity-name="User2Object">
         <id name="_id" access="field" column="id">
            <generator class="assigned"/>
         </id>
        <property name= ...>
</class>
</hibernate-mapping>

Then depending on which type of entity you need you call the appropriate session methods as:

_session.Save("User1Object", user1)

or

_session.Save("User2Object", user2)

Posts 2 & 3 were used as a basis for this snippet. Official source [4]

After match:

One answer on the first question which is actually link to this post [5] there is different approach:

You say bye to the first instance of the object, clone the data to fresh instance and persist that with different name. Thus, no violation on Hibernate logic and everybody content: same data at two tables and no sub-classes used.

Well, the implementation or code or credibility of that approach is so and so, I haven't tested it neither.

Another case:

In this post [6] there is another person trying to challenge the super class approach with something simpler, but again, the most credible answer states it is not possible another way around, the official non-xml approach is the said subclass approach.

Sources

[1] How to map one class to different tables using hibernate/jpa annotations

[2] Map Two Identical tables ( same schema...) to same entity in Hibernate

[3] How to map 2 identical tables (same properties) to 1 entity

[4] http://docs.jboss.org/hibernate/core/3.2/reference/en/html/mapping.html#mapping-entityname

[5] Hibernate 4: One class mapping Two tables - How to persist one object on both tables?

[6] Hibernate Annotation for Entity existing in more than 1 catalog

Answer 2

Also it works using a default entity and an alternative one:

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
   <class name="DomainModel.User, DomainModel"
     table="User1Object">  
         <id name="_id" access="field" column="id">
             <generator class="assigned"/>
         </id>
        <property name= ...>
 </class>
 <class name="DomainModel.User, DomainModel"
     table="User2Object" entity-name="User2Object">
         <id name="_id" access="field" column="id">
            <generator class="assigned"/>
         </id>
        <property name= ...>
</class>
</hibernate-mapping>

For the default one, you can use the method

_session.Save(user1)

and

_session.Save("User2Object", user2)

for the alternative one.