Hi Bruno
All squares are rectangles, but some rectangles are squares, the query
for rectangles will also give you squares. This is a valid result from
cayenne's perspective.
What you looking for is to query for Rectangle but not Square. I see
three ways of doing that:
- query for Parent, query for Child, subtract results from each other.
(performQuery(Rectangle).removeAll(performQuery(Square))
- create another subclass of Parent, mutually exclusive with Child, and
query that. (performQuery(NotSquare))
- expose the qualifier field in cayenne modeler, query with the
qualifier. (performQuery(Rectangle,
ExpressionFactory.noMatch(polygonType, square))
With regards
Marcin
On 6/03/11 11:18 PM, Bruno René Santos wrote:
Both parent and child are the same on the database level. But each
object is used differently on the GUI level. As both GUIs must
cohexist temporarily I thought I could do a child object from the
current used object and change some logic on it. So i got something
like this
Child extends _Child
_Child extends Parent
Parent extends _Parent
_Parent extends CayenneDataObject
The only issue here (at least I think...) is that a performQuery(new
SelectQuery(Child.class)) will correctly return a list of Child but a
performQuery(new SelectQuery(Parent.class)) will also return a List of
Child... Any way to return a List of Parent?
Thanx
Bruno
Em 06-03-2011 10:15, Aristedes Maniatis escreveu:
On 6/03/11 9:03 PM, Bruno René Santos wrote:
I have an object structure with a Child dataobject which inherits
from a Parent which is linked to a db_entity. I am trying to use the
Parent on a GUI and the Child on another GUI. The Child overrides
some methods from the Parent (but the db table is the same) and so
is mandatory that on each GUI their respective searches yeld Child
objects or Parent objects. On the GUI that uses the Child everything
goes according plan, the performQueries return lists of Children.
But on the Parent GUI I call
context.performQuery(new SelectQuery(Parent.class))
but the method returns also a list of Children, which are
incompatible with the parent GUI. Is there any way that this query
returns Parents instead of Children? I was trying these inheritance
so that i could reuse all db fields and relationships from the
parent on the child.
What does the discriminator column say about these objects? Are they
actually Child entities in the database or Parent? They can't be both
at the same time.
This isn't like plain-old Java inheritance where you can just cast
from one to the other as needed. If you could, what would happen if
you queried for a list of Child objects, casting them as Parents,
changed some Parent attribute and committed the context? Would they
now become Parents in the database?
Ari
