Hi Marco,
Unfortunately there's no way to *map* a persistent property that can be read
into an object, but ignored on updates. One possible solution is to use the new
multi-result ObjectSelect from 4.0.M6 to fetch extra values together with
corresponding persistent objects and then manually copy them into a
non-persistent property of each object. E.g.:
// define some reusable metadata
Property<MyEntity> self = Property.createSelf(MyEntity.class);
Property<Long> relCount = MyEntity.RELATED_LIST.count();
// build and run query
Object[] result = ObjectSelect
.columnQuery(MyEntity.class, self, relCount)
.select(context);
// postprocess the result
List<MyEntity> finalResult = result
.stream()
.map(array -> {
MyEntity e = array[1];
e.setXyz((Long) array[0]);
return e;
}).collect(Collectors.toList());
Whether this will work or not depends on what SQL function you need there
(Cayenne will need to support it [1]), and will also not work is MyEntity is
retrieved via a relationship instead of a query that you can control.
Maybe someone will chime in with a better workaround?
Andrus
[1]
https://github.com/apache/cayenne/blob/master/cayenne-server/src/test/java/org/apache/cayenne/exp/FunctionExpressionFactoryTest.java
> On May 10, 2017, at 1:09 AM, Marco A Gonzalez <[email protected]> wrote:
>
> Hi,
> We’re using Cayenne 4.0 with PostgreSQL and for various reasons need to use a
> read-only column whose value is calculated by a SQL function.
>
> Accessing the column value using a simple SELECT clause works great. Also,
> when generating the SQL for an UPDATE statement, Cayenne is smart enough not
> to include the columns whose values haven’t changed. Since we haven’t figured
> out how to mark a column as read-only in Cayenne Modeler, Cayenne includes it
> when generating the SQL for the INSERT statement which obviously fails
> (because there’s no place for the value to be stored).
>
> Is there a way to mark a column as read-only, even if we have to edit the
> relevant XML file by hand?
> If this isn’t the way to do it, is there a way to tell Cayenne NOT to include
> the column when generating the SQL for an INSERT/UPDATE statement?
>
> - Marco A.
>
>
