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Re: Using EO
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Re: Using EO


  • Subject: Re: Using EO
  • From: Chuck Hill <email@hidden>
  • Date: Wed, 25 May 2005 09:25:36 -0700

I'll follow up on Jerry's reply with a focus on Jon's comment, "I guess my only question is which way has the best performance. " This is a common concern for new comers to WO and IMHO a common mistake. Heed Jerry's advice: get your objects well designed and working and only then and only if you see a real problem, start to optimize. I recall someone else who wandered in here with the same concerns. Again and again I said "don't worry about optimization". Finally, he relented, but there was a lot of fretting. :-) After he finally deployed, he came back with the comment "It's so fast that my user's won't believe that it is a real, deployed web app and not a local demo."

Chuck


On May 25, 2005, at 6:27 AM, Jerry W. Walker wrote:

Though I don't disagree with specific point made in this thread, I hate the direction that it has taken.

If this is your first WO project, then there are a few reasons to do this without using raw SQL. Probably the first, and foremost, is to get used to doing things with objects rather than with tables. My first concern is the statement of the original question:

"is there a way to build a FetchSpecification that would accomplish the sql equivalent of "SELECT SUM(COLUMN_NAME) FROM TABLE_NAME"

This question is clearly framed from the perspective of "I have a table of rows with which I want to do something, now how do I get WO to help me do that thing to my table in the same way I've always done these things with SQL?"

Experienced WO developers would think instead of the object graph that we are manipulating in our object oriented java application rather than the rows we have stored in our relational database. Rephrasing the question, "I have a set of objects 'O' with an attribute 'a'. How do I obtain the sum of that attribute across those objects?"

The obvious first answer is Sacha's first answer:

"My preferred method is to use the NSArray @sum key value coding (note: no need to do an enumeration). "

Perhaps those objects have already been cached and we don't need to fetch raw rows. Perhaps the sum could be obtained as a side effect of another necessary operation on those objects later when they have already been fetched.

Failing either of those two possibilities, I would still first write the fetch without referencing raw rows and get it to work. Finally, if the result is clearly taking too long, I would profile where the delays are occurring and, if in database fetches, then would start to consider raw rows. The point being that referencing raw rows is a last resort rather than a way to move into the comfort zone of old habits with result sets.

So what are the down sides to just moving immediately to raw rows?

  * a missed opportunitiy to get used to the WO way

* the short circuiting of several elegant features built into WO to help one deal with objects rather than rows

* the higher probability of weak object oriented design built up from this raw row decision

I'm sure others could add more with a little more thought, but I have to catch a train.

Good luck with WebObjects and welcome to the fold.

Best regards,
Jerry


On May 25, 2005, at 3:37 AM, Sacha Mallais wrote:

On May 25, 2005, at 12:15 am, Jonathan Miller wrote:

Hmm... I guess my only question is which way has the best performance. To answer my own question I would assume it to by passing raw SQL. This is my first web site with WO and I was hoping I could avoid doing that however(it's just too cool not to have to use SQL).

My preferred method is to use the NSArray @sum key value coding (note: no need to do an enumeration). However, if you have many many values to aggregate, then you're best bet is indeed raw SQL.


sacha


On May 24, 2005, at 5:19 PM, Sacha Mallais wrote:

On May 24, 2005, at 8:00 pm, Jonathan Miller wrote:


is there a way to build a FetchSpecification that would accomplish the sql equivalent of "SELECT SUM(COLUMN_NAME) FROM TABLE_NAME"

I know you can select the objects and then add them using a java enumeration but I was wondering if there is another way.


The most obvious is to construct the SQL yourself and send it directly using the low-level EOF stuff (or even the JDBC stuff...). I mention it because, as WO developers, we sometimes forget that there's SQL back there ;-)

A more interesting (if not hackish...) way to accomplish this would be to create a new entity with the same table name and a single derived attribute of "sum(column_name)". You can then either generate a full Java class for that or just use raw rows.

Also, the PracticalWO frameworks (and the GVC frameworks -- also to be released soon, and, come to think about it, probably the ProjectWOnder frameworks too...) have a helper method that makes aggregate queries more simple.

HTH,


sacha


-- Sacha Michel Mallais - 400 lb. chimp Global Village Consulting Inc.: http://www.global-village.net/ 1. Never tell everything at once. -- Ken Venturi, Ken Venturi's Two Great Rules of Life



-- Sacha Michel Mallais
President / Developer Extraodinaire
Global Village Consulting Inc.  http://www.global-village.net/
The bird of paradise alights only upon the hand that does not grasp.

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Practical WebObjects - a book for intermediate WebObjects developers who want to increase their overall knowledge of WebObjects, or those who are trying to solve specific application development problems.
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  • Follow-Ups:
    • Re: Using EO
      • From: James Cicenia <email@hidden>
    • Re: Using EO
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      • From: Ken Anderson <email@hidden>
References: 
 >Using EO (From: Jonathan Miller <email@hidden>)
 >Re: Using EO (From: Sacha Mallais <email@hidden>)
 >Re: Using EO (From: Jonathan Miller <email@hidden>)
 >Re: Using EO (From: Sacha Mallais <email@hidden>)
 >Re: Using EO (From: "Jerry W. Walker" <email@hidden>)

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