Thanks for responding Brian. I finally got a chance to download the
latest version and checkout your suggestions. I'm afraid I still
only see support for one-to-many and many-to-many relations.
The samples show Customer and Address in a one-to-many relation
rather than a one-to-one relation. Easy enough to get the Address
for a Customer. A bit harder to get a Customer for a given Address.
Imagine that the Customer-Address really is a one-to-one relation.
The way I am doing it now (which is not at all terrible) is to setup
a one-to-many (just like the sample) and then add a getRecord()
function to Address which calls getIterator() and then gets the first
and only Customer from the Iterator. As I said, it's not terrible...
just a lot of unnecessary CPU cycles spent.
Am I missing something?
=dave=
On Mar 14, 2006, at 5:48 AM, Brian Hegeman wrote:
There is definitely support for one-to-one relationships. Check
Doug's excellent documentation included in the download -- page 46
has some examples of using <hasOne...> connections. Basically it
works just like you've suggested but check the samples.
brian
David A. Cheslow PhD wrote:
Hi again;
Still loving reactor Doug! Keep up the great work!
Support for Many-to-Many and One-to-Many relations seems pretty
complete... noticeably missing is support for One-to-One relations.
Only one of the tables involved in a one-to-one relation needs to
contain a foreign key to the other table. Relational algebra
does not help us choose which table gets the extra field, but
domain knowledge usually makes it obvious. Adding a "back pointer
foreign key" from the other table creates ugly problems with
cascades and creates a lot of unnecessary work. Knowing that the
relation is one-to-one allows the "back reference" to be
calculated... just as it is for the "many" side of a one-to-many
relation.
Let's say that 'Person' as a one-to-one relation with 'Address'.
We store a foreign key to the Address table in the Person table
(we could just as easily store a foreign key to Person in
Address... but that makes less sense, for some reason). Reactor
allows us to call getAddressRecord() on a PersonRecord... but it
does not allow us to call getPersonRecord() on an AddressRecord,
even though all the needed information is available.
Syntactically, this could be supported the same way that it is for
Many-to-Many relationships. For example, something like:
<object name="person">
<hasOne name="address" alias="homeaddress">
<relate from="homeaddressId" to="addressId" />
</hasOne>
</object>
<object name="address">
<hasOne name="person" alias="whereILive">
<link name="person" from="addressid"
to="homeaddressid" />
</hasOne>
</object>
There are two patterns in which I frequently use one-to-one
relations: when a sub-element repeats in an object (e.g. person
has-one 'homeaddress' AND person has-one 'workaddress') and for
storing object hierarchies in a RDB (each instance has a one-to-
one relation with an instance of it's superclass).
Adding this functionality outside of reactor is trivial, but it
would also be trivial to add it into reactor...
Just food for thought, love the reactor,
=dave=
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