Re: [OJB-developers] "constant" values in where clause

[Thomas M. <tho...@ho...>]

Hi Matt,

> Matt Goodall wrote:
> 
> Hi,
> 
> I'm still trying to understand what's actually possible with OJB ...
> 
> If I have a table defined something like this:
> 
>     type varchar(xxx)
>     short_name varchar(yyy)
>     long_name varchar(zzz)
> 
> which might hold the following:
> 
>     "vehicle", "car", "small thing which can't seem to hold more that
> one person at a time"
>     "vehicle", "train", "long thing which is always late"
>     "fruit", "apple", "green or red round thing"
>     "fruit", "mango", "yum, yum"
>     "fruit", "banana", "yellow, long and bendy. great with custard"
>     ... etc, I'm sure you get the idea by now ;)
>

When I get you right you want to map different Java classes (Vehicle,
Fruit) onto one table.
The column "type" is used as a type identifier.
This is a scenario is described in tutorial3 in section "mapping
inheritance hierachies" in the subsection "mapping all classes on the
same table".

By default OJB expects a full qualified classname in the column "type".
If this is not viable for your, you can implement a RowReader with a
special implementation of the method selectClassDescriptor(...). This is
needed to map your names "vehicle" and "fruit" to real classnames like
"my.own.com.Vehicle" and "my.own.com.Fruit".
 
> Can I tell OJB that I have a class called Fruit with public name and
> description properties and ask OJB for all Fruit (for example) without
> having to qualify that type='fruit' i.e. supply no Criteria to the
> query and only get a list of fruit back?
> 

// select all fruits:
Query q = QueryFactory.newQuery(Fruit.class, null);

HTH,

Thomas

> Thanks, Matt
> ---
> Matt Goodall
> Analyst Programmer, Strategic Systems Solutions
> e: mat...@ss..., t: +44 113 3892645
>