Re: getting the results of a sub select
Re: getting the results of a sub select
- Subject: Re: getting the results of a sub select
- From: Ken Anderson <email@hidden>
- Date: Tue, 15 Mar 2005 07:55:38 -0500
Ted,
You need to think of jobs and clients as objects that have
relationships to each other. If you continue to think about things in
terms of SQL and specialized queries, you're going to have a hard time
with EOF (the database layer of WebObjects).
What you need to do is define a relationship in EOModeler between job
and client, using ccode and acode to define the relationship.
If you call the relationship 'client', then you can display the client
name with:
client.cname
When you fetch a bunch of jobs, EOF creates something called a fault in
place of the client relationship. When you ask a job for client.cname,
if client is still a fault, it will go to the database and fetch that
particular client.
One thing that's important to realize here is that, by default, EOF
will make a trip to the database for each client you need to fetch. If
you're displaying client.cname in a table or something, that can become
very inefficient. I suggest you inspect the Client entity in
EOModeler, choose the advanced entity inspector, and set the batch
faulting size to a number you find reasonable. What this will do is
fetch that many clients when one is fetched, which will improve your
performance significantly.
I highly suggest reading this to get more familiar with how EOF works:
http://developer.apple.com/documentation/WebObjects/Enterprise_Objects/
index.html
Ken
On Mar 15, 2005, at 7:45 AM, Theodore Petrosky wrote:
I am rather new to this so please be gentle....
I finally have an interface with webobjects talking to
my postgresql db. I am having a problem with a sub
select.. in schema, i have a job table and a client
table. the job table of course has a primary key of
the jobnumber. the client table has a PK of the
clientcode. each job row is assigned to a clientcode.
in cocoa I can do...
select jobnumber, (select cname from clientinfo ci
where ci.ccode = j.acode) as clientname, shortdesc
from jobinfo j order by jobnumber;
works great...
I am using the marker book and a few others and I just
can not seem to grasp how to populate my table in
webobjects. It appears to be a WOtoOneRelationship (I
think).
the end result should be:
jobnumber clientname shortdesc
of course I can easily get
jobnumber clientcode shortdesc
could someone point me in the right direction.....
thanks,
Ted
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