Doubt - Oreilly - Page 107

[Niranjan Deshpande]

Hi all,

Plesae refer Oreilly - Page 107

All the three things - pkColumnName valueColumnName pkColumnValue are confusing me.

Functionally, what is the difference between these three.

It would be great if some one draws a relevant table here and explains me

[Alex Kikhtenko]

Originally posted by Niranjan Deshpande:
Hi all,

Plesae refer Oreilly - Page 107

All the three things - pkColumnName valueColumnName pkColumnValue are confusing me.

Functionally, what is the difference between these three.

It would be great if some one draws a relevant table here and explains me

The schema is simple as a pie.

Have a look at the following table:

---------------------------------------
|   PK_COLUMN    |    VALUE_COLUMN    |
---------------------------------------
| DETERMINANT1   |  3                 |
| DETERMINANT2   |  5                 |
| DETERMINANT3   |  7                 |
---------------------------------------

So, the layout is:
pkColumnName = "PK_COLUMN"
valueColumnName = "VALUE_COLUMN"
pkColumnValue = "DETERMINANT2" (for example)

The idea is each row in the table represents certain entity and there must be the way to distinguish between entities (3 entities in the preceding example)
[ February 09, 2008: Message edited by: Alex Kikhtenko ]

[Niranjan Deshpande]

Thanks for that..

But its still unclear to me !!

Please explain the schema keeping in mind the example entiy in oreilly.
Will be grateful

What is the CUST_ID in the Oreilly code? Please explain the schema with reference to the code in the book

[Alex Kikhtenko]

Ok. Let's consider the book's example with Customer entity.

@Entity
@TableGenerator(name="CUST_GENERATOR"
                   table="GENERATOR_TABLE"
                   pkColumnName="PRIMARY_KEY_COLUMN"
                   valueColumnName="VALUE_COLUMN"
                   pkColumnValue="CUST_ID"
                   allocationSize=1)
public class Customer implements java.io.Serializable {
    ...
}

Suppose we have another one entity Product:

@Entity
@TableGenerator(name="CUST_GENERATOR"
                   table="GENERATOR_TABLE"
                   pkColumnName="PRIMARY_KEY_COLUMN"
                   valueColumnName="VALUE_COLUMN"
                   pkColumnValue="PROD_ID"
                   allocationSize=1)
public class Product implements java.io.Serializable {
    ...
}

As you can see we want the both entities to use the same table GENERATOR_TABLE to hold their Primary-Key-Next-Value.

Suppose also we've just persisted 3 Customer entities and 8 Product entities into the DB.

In this case the GENERATOR_TABLE table would look like:

------------------------------------------------
|   PRIMARY_KEY_COLUMN    |    VALUE_COLUMN    |
------------------------------------------------
|        CUST_ID          |  4                 |
|        PROD_ID          |  9                 |
------------------------------------------------

So obviously CUST_ID is necessary to distinguish it's primary key value from primery key value of Product entity bean.

Hope this helps.