Re: Mapping multiple EOs to one table
Re: Mapping multiple EOs to one table
- Subject: Re: Mapping multiple EOs to one table
- From: Ricardo Strausz <email@hidden>
- Date: Mon, 18 Aug 2003 17:32:50 -0500
What is the scope of an EOGlobalID??
Isn't the application?
If so, two concurrent users, with different app id, will have not
problem.
Supposing this is correct, the problem may ocure with a single user (in
a single app) tring to see the hole row, but from different
scenarios... is it?
But then, the logic most prevent him to use a "bigger" scenario in
which s.he can see the hole object (and do a fetch ---or refault---)
from the parent entity...
Am I loosing something?
Dino
On lunes, agos 18, 2003, at 17:11 America/Mexico_City, Chuck Hill wrote:
When EOF fetches an object it associates the snapshot with the entity
type through the EOGlobalID. If you fetch a row from that table
containing the same PK then EOF will not change its mind about what
class it is. So you could do a fetch for EntityA but get instances of
EntityB returned instead. That is why you don't want to do this.
Don't treat entities as database views.
Chuck
Ricardo Strausz wrote:
On lunes, agos 18, 2003, at 16:10 America/Mexico_City, Jonathan
Rochkind wrote:
I'm doubtful that single table inheritance will work for you. The
EOF inheritance scheme assumes that each row represents a certain
class, and doesn't change back and forth. You have rows that really
are all classes at once, it's not that certain rows are certain
classes. It's that they're all at once, but you just don't want to
fetch all the data in at once. I don't think you are going to be
able to use EOF inheritance in a way that achieves your goals
(doesn't fetch in all columns at once), but doesn't cause any
problems. That's too far from what it's intended for, I think.
I do not undestud your concern...
Say I have a table with four columns: PK, date, anInt & aFloat
and I want to see it in two different scenarios: in the first only
PK, date & anInt, and in the second PK, date & aFloat.
I can make a parent entity with PK & date and two childs (each with
the extra column added as an atribute), all mapped to the same
table...
I think that the only thing to be cocerned here is to alow those
extra atributes to be NULL in the database...
Dino
But I haven't been able to think of a better solution either. You
might be best off just moving your data to a number of different
tables, instead of having them all in one table.
With your previous design, having multiple EOEntities that are
really the same table, you could try something like: Designate of
your entities as the 'primary' one. Only this one will ever be
inserted. It has relationships to the other entities, that are
really relationships to other 'parts' of the same row the source EO
represents. Follow these relationships to get these other parts;
don't ever insert EOs of these other entities. Still not sure that
will work. Monkeying around with the 'propagate primary key' and
'mandatory' and 'owns destination' attributes on the relationships
from this 'main' entity to the other ones might get you somewhere
too. But I'm not too optimistic about it myself.
--Jonathan
At 08:23 AM 8/19/2003 +1200, Ray Ackland wrote:
Well, even though many of the tables will only be sharing one
common field (primary key) I guess what we are looking at is really
single table inheritance. This could be the way to go. Seems to
meet all the criteria - the parent class is just the primary key
field.
I will definitely try it and tell you what happens. That gives me
much more optimism.
Ray.
On Tuesday, Aug 19, 2003, at 06:08 Pacific/Auckland, Ricardo
Strausz wrote:
Just guessing...
but first, does you multiple views of the same table inherits from
one the other?
It may be that, if you want to have different views from the same
table, define different childs for it (and not simply unrelated
entities which may confuse EOM).
Hope it helps! let us know
Dino
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--
Chuck Hill email@hidden
Global Village Consulting Inc.
http://www.global-village.net
Progress is the mother of all problems.
- G. K. Chesterton
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