It should be possible to use "DerviedDbEntities" - see this button on
the Modeler toolbar:
http://objectstyle.org/cayenne/images/modeler/icon-derived-dbentity.gif
But since DerviedDbEntities are a temporary and very limited feature
and I would very much like to get rid of them, replacing them with
something cleaner, my own preferred solution would be to map a
SQLTemplate query in the Modeler that does what you need in SQL.
Andrus
On Jan 14, 2006, at 6:57 AM, Dirk Lattermann wrote:
> Hello,
>
> I'm using Cayenne1.2M10. I've got a data object class X with a to-
> one relation toX to the same data object class X (I don't think
> that the relation being reflexiv matters here). The corresponding
> inverse to-many relationship xArray is also defined.
>
> Now I would like to select the objects that aren't referenced by
> any other objects, i.e. their xArray is empty.
>
> In SQL, I would write a query like
>
> select * from x x1 where not exists (select 'X' from x x2 where
> x2.ref_to_x = x1.pk_x)
>
> One could also imagine an outer join of x x1 and x x2 on the above
> condition and selecting the rows with x2.pk_x is null.
>
> How can I achieve this using a SelectQuery? I tried it with a
> qualifier of
>
> qual = ExpressionFactory.matchExp("xArray", null);
> or
> qual = ExpressionFactory.matchExp("xArray.anyNotNullProperty", null);
>
> but that failed. The first one results in the query
> SELECT DISTINCT t0.col1, t0.col2, t0.pk_x, t0.ref_to_x FROM x t0, x
> t1 WHERE t0.pk_x = t1.ref_to_x AND (t0.pk_x IS NULL)
> obviously, this returns no rows.
>
> Is there probably the possibility to define a "calculated" property
> of class X that returns the size of the xArray List? I tried this,
> but I got
>
> org.objectstyle.cayenne.exp.ExpressionException: [v.1.2M10 January
> 5 2006] Can't resolve path component: [X.arraySize].
>
> I don't know if it's possible to add an obj-attribute to an obj-
> entity in the data map xml file that doesn't reference a db-
> attribute-path.
>
> Thank you,
> Dirk Lattermann
>
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