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Java Toplink Essential -

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  Java Toplink Essential - "nicola" <nicola@THRWHITE.remove-dii-this> - 2011-04-27 15:22 +0000
    Re: Java Toplink Essentia "Martin Gregorie" <martin.gregorie@THRWHITE.remove-dii-this> - 2011-04-27 15:22 +0000
      Re: Java Toplink Essentia "Lew" <lew@THRWHITE.remove-dii-this> - 2011-04-27 15:22 +0000
        Re: Java Toplink Essentia "Arved Sandstrom" <arved.sandstrom@THRWHITE.remove-dii-this> - 2011-04-27 15:22 +0000

#237 — Java Toplink Essential -

  To: comp.lang.java.databases
In my db there are some tables like

TABLE1_2006 (ID, CODE, VOLUME)
TABLE2_2007 (ID, CODE, VOLUME)
TABLE3_2008 (ID, CODE, VOLUME)

They are equal but have diffferent name. In fact these tables are
created
every year (as you can see).
In this sense they use the same entity

public class MyEntity implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @Column(name = "ID", nullable = false)
    private Integer id;
    @Column(name = "CODE")
    private String code;
    @Column(name = "VOUME")
    private String volume;

...
...
...
}

I need to obtain different list of entities relative to all tables in
the same database;
can I change table name of my entity at runtime ?


Thanks

Nicola

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#238 — Re: Java Toplink Essentia

  To: comp.lang.java.databases
On Wed, 10 Sep 2008 01:23:48 -0700, nicola wrote:

> In my db there are some tables like
> 
> TABLE1_2006 (ID, CODE, VOLUME)
> TABLE2_2007 (ID, CODE, VOLUME)
> TABLE3_2008 (ID, CODE, VOLUME)
> 
> They are equal but have diffferent name. In fact these tables are
> created
> every year (as you can see).
> In this sense they use the same entity
> 
> public class MyEntity implements Serializable {
>     private static final long serialVersionUID = 1L; @Id
>     @Column(name = "ID", nullable = false) private Integer id;
>     @Column(name = "CODE")
>     private String code;
>     @Column(name = "VOUME")
>     private String volume;
> 
> ...
> ...
> ...
> }
> 
> I need to obtain different list of entities relative to all tables in
> the same database;
> can I change table name of my entity at runtime ?
> 
> 
Declare a view  over all the tables and enquire on that.

But, why on earth use multiple tables? They don't do anything that a 
single table with a YEAR column couldn't do while managing to make at 
least one task more difficult as you've just demonstrated.


-- 
martin@   | Martin Gregorie
gregorie. | Essex, UK
org       |

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#239 — Re: Java Toplink Essentia

  To: comp.lang.java.databases
nicola wrote:
>> In my db there are some tables like
>>
>> TABLE1_2006 (ID, CODE, VOLUME)
>> TABLE2_2007 (ID, CODE, VOLUME)
>> TABLE3_2008 (ID, CODE, VOLUME)

Martin Gregorie wrote:
> Declare a view  over all the tables and enquire on that.
> 
> But, why on earth use multiple tables? They don't do anything that a 
> single table with a YEAR column couldn't do while managing to make at 
> least one task more difficult as you've just demonstrated.

I feel suspicion when I read about inherited tables in a DBMS, such as in 
Postgres.  At first blush the OP's situation seemed to me like an 
inherited-table scenario.  I felt about as I might encountering an escaped 
specimen from Dr. Moreau's island.

I used to feel that way about automated object-relational mapping (ORM) 
packages, but JPA alleviates that.  There is a dichotomy between the world 
view of object-oriented programming and that of relational database 
architecture.  Inherited tables seem out of place to me - object-oriented 
monstrosities in a data world.  Multiple identical tables are like that also - 
if the data structures are the same and have the same interpretation, that 
argues for a single logical table.  Martin's suggestion is spot on, and 
completely harmonious with the data-world outlook.

I don't know of a term analogous to "normal form" (as in "third normal form") 
for excessive splitting of tables into many tables; all the normal forms have 
to do with insufficient splitting.  Advances in the database world occur in 
how to structure data - relations, normal forms, star schemae, foreign keys, 
these are the building blocks of DBMSes as classes and objects are of O-O 
programming.

How one structures data for a database is different from how one structures 
objects for a program.

-- 
Lew

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#250 — Re: Java Toplink Essentia

  To: comp.lang.java.databases
"Lew" <noone@lewscanon.com> wrote in message 
news:cqWdnWKfq97dBlXVnZ2dnUVZ_rCdnZ2d@comcast.com...
[ SNIP ]
> I don't know of a term analogous to "normal form" (as in "third normal 
> form") for excessive splitting of tables into many tables; all the normal 
> forms have to do with insufficient splitting.  Advances in the database 
> world occur in how to structure data - relations, normal forms, star 
> schemae, foreign keys, these are the building blocks of DBMSes as classes 
> and objects are of O-O programming.
[ SNIP ]

I've seen this particular operation - splitting one table into many tables 
based on the value of an attribute, and dropping that column - described as 
"attribute splitting". As I understand it this violates Domain Key Normal 
Form (DKNF), because not all of the logical decisions your program would 
want to make are defined by the data.

I'm leery of any approach where domain information is captured only in the 
names of files or database tables. Even when using flat files I'd still want 
to have a header line with information like this.

If the boss absolutely wanted this kind of splitting I'd at least argue for 
keeping a year column in each table, even if it's all the same value for 
each table.

AHS

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