AW: AW: AW: AW: [Objectbridge-developers] Q: How to setup the dat abas e?

[Mahler T. <tho...@it...>]

> -----Urspr=FCngliche Nachricht-----
> Von: Ivan Toshkov [mailto:to...@cr...]
> Gesendet: Mittwoch, 8. August 2001 16:33
> An: Mahler Thomas
> Betreff: Re: AW: AW: AW: [Objectbridge-developers] Q: How to setup =
the
> databas e?
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> Hi again,
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> I couldn't find an example of using OJB with an hierarchy of classes.
> The only exception is test.ojb.broker.Article and
> test.ojb.broker.BookArticle, but the latter does not add any=20
> new fields,
> so it's not exactly what I'm looking for.
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It does! BookArticle has two additional attributes:
	/** books author*/
	private String author;
	/** ISBN No of Book*/
	private String isbn;

(VisualAge does not keep all attributes at the top of a class =
definition. I
guess that's why you did not find those attributes.)

There is also the class CdArticle that does not extend Article but
implements the interface Article and introduces also two more =
attributes
than Article.

> To be more specific, let's say we have the following classes:
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> abstract class A
> {
>   int num;
> }
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> class B extends A
> {
>   String name;
> }
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> class C extends A
> {
>   int count;
> }
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> The theory says, there are generally 3 representations:
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> 1. Store the whole hierarchy in one table:
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> table A:
> +-----+-----+------+-------+------+
> | oid | num | name | count | type |
> +-----+-----+------+-------+------+
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supported by OJB. In the ClassDescriptor of each class you just have to
declare that it maps to table A.

> 2. Store each concrete class in separate table:
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> table B:
> +-----+-----+------+
> | oid | num | name |
> +-----+-----+------+
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> table C:
> +-----+-----+-------+
> | oid | num | count |
> +-----+-----+-------+
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supported by OJB.
In the ClassDescriptor for class B you have to declare that it maps to =
table
B (same for Class C and table C).

> 3. Store each class in a separate table:
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> table A:
> +-----+-----+
> | oid | num |
> +-----+-----+
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> table B:
> +-----+------+
> | oid | name |
> +-----+------+
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> table C:
> +-----+-------+
> | oid | count |
> +-----+-------+
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not directly supported. Could be relaized via a foreign key relation.

HTH,

Thomas=20

> Which of these are currently supported by OJB and how do the XML
> description looks like?
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> Best regards,
> Ivan
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