Hi,
The management summary answer to your question "is it important to
support alias-names in order by and having clause" is : Yes, it is
really really really important!!!
So now for some background information explaining our situation.
We implemented a concept to support non-modelled (abstract) attributes.
We need to support many different complex forms and datasets for our
customers. The deviation between customers is huge, so modifying our
domain model (and thus our pojos and thus out database tables) for every
customer implementation is not an option. We need to have a stable core
domain model.
So all our objects in our domain model have a collection property that
is capable of holding a collection of abstract-attribute instances, it's
a standard 1:N relation which OJB supports. Abstract attribute classes
are classes implementing name-value tuples, the name of the attribute,
and the value of the attribute. So adding new attributes to specific
objectclass instances implies we just have to add abstract attribute
instances to the collection and OJB will store them in the apropriate
table in the database. We do not have to modify our domain model by
adding new java properties to the affected classes and adding new
columns to the affected tables.
So querying for values of object properties, represented by abstract
attributes, we need to create clauses combining the name/value
properties of the abstract attribute instances.
So an example query with two selection criteria based on abstract
attributes of an object could be:
SELECT * FROM PERMIT AS A0 INNER JOIN PERMIT_ABSTRACT_ATTRIBUTE AS A1
INNER JOIN PERMIT_ABSTRACT_ATTRIBUTE AS A2
WHERE A0.ID=A1.ID AND A0.ID=A2.ID AND
(A1.NAME='<name of attribute 1> AND A1.VALUE='<value of attribute
1>') AND
(A2.NAME='<name of attribute 2> AND A2.VALUE='<value of attribute
2>');
Since we need to work with bounded name/value pairs, we need to bind
them together using a alias, in this example the aliases are A1 and A2.
So if we want to order the resultset on such an abstract attribute value
the query would look like:
SELECT * FROM PERMIT AS A0 INNER JOIN PERMIT_ABSTRACT_ATTRIBUTE AS A1
INNER JOIN PERMIT_ABSTRACT_ATTRIBUTE AS A2
WHERE A0.ID=A1.ID AND A0.ID=A2.ID AND
(A1.NAME='<name of attribute 1> AND A1.VALUE='<value of attribute
1>') AND
(A2.NAME='<name of attribute 2> AND A2.VALUE='<value of attribute
2>')
ORDER BY A2.VALUE;
We need to use the alias to link the orderby to the proper join, of
which there are two, to the same join table (the abstract attribute
table)!
This is rather common functionality, currently supported in all our
applications, supported by OJB 1.0rc6 that we use (the 1.0 release
itself was not stable enough for us). In fact, I helped implementing
this feature in OJB a long time ago, and I believe the documentation on
the OJB site is the documentation I once sent to you guys.
The upcoming 1.0.5 release has some features that we have been waiting
for, for several years. We have been able to postpone improvements in
our applications for this long, but we cannot do this any longer. So we
really need these new features 1.0.5 implements, but we need the
user-alias in the orderby to work as well, otherwise we will loose a lot
of functionality and our customers will not accept that.
Some of the required features are the native limit-clause
implementations, the reference descriptor implementation without using
foreign-keys (I requested this feature for more then a year ago myself),
etc., etc..
I hope you now have an understanding of how we use this feature, and
that we cannot afford to loose it.
Greetings,
Roger Janssen
iBanx
*************************************************************************
The information contained in this communication is confidential and is intended
solely for the use of the individual or entity to whom it is addressed.You
should not copy, disclose or distribute this communication without the
authority of iBanx bv. iBanx bv is neither liable for the proper and complete
transmission of the information has been maintained nor that the communication
is free of viruses, interceptions or interference.
If you are not the intended recipient of this communication please return the
communication to the sender and delete and destroy all copies.
---------------------------------------------------------------------
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]
