Objects, REFs, and Oracle collections

Post #114,715 by admin 8/21/03 9:30:18 AM Reply	Objects, REFs, and Oracle collections We're trying to develop a way to hold a set of base type objects in a collection in PL/SQL. The basic idea is a collection of buffer objects, where the objects could be single string objects or other complex subtypes of a buffer object. However, from the looks of it if you declare a collection of a particular base type and put a subtyped object in, the object turns into a base type object. Whoops. One might try to use REFs... however, REFs can't be used without an object table or view, so they're useless for in-memory transient stuff. Any ideas? Regards, -scott anderson "Welcome to Rivendell, Mr. Anderson..."
Post #114,786 by ChrisR 8/21/03 2:14:19 PM 8/21/03 2:20:17 PM Reply	Will TREAT not work? Slightly modified from the [link\|http://www.angelfire.com/tx4/cus/shapes/plsql.html\|Shapes junk]: rect := TREAT(scribble(1) AS rectangle); rect.setHeight(50); rect.draw(); Or is the problem that you can't retrieve what subtype was stored in the collection? Edited by ChrisR Aug. 21, 2003, 02:20:17 PM EDT Expand All History
Post #114,793 by admin 8/21/03 2:44:33 PM Reply	Interesting... Oracle documentation says that TREAT is not supported in PL/SQL... Regards, -scott anderson "Welcome to Rivendell, Mr. Anderson..."
Post #114,797 by ChrisR 8/21/03 2:52:30 PM Reply	Just playing around It does seem idiosyncratic. In the first place, you have to use assignment - casting doesn't work in-line. Means that the following won't compile: TREAT(scribble(1) AS rectangle).setHeight(60); Guess you could work around that by just using assignment. Also, a simple assignment copies the object as a clone. Any modifications are not applied to the original object. Means that if you drew the original base object, it remains unmodified after the setHeight instruction: scribble(1).draw(); Still fumbling my way around PL/SQL, but would it require a REF of some sorts to make the scribble(1) and rect vars point to the same memory location?
Post #114,798 by admin 8/21/03 2:57:15 PM Reply	The problem with REFs: They're only usable on table objects, not transitory objects. Copying the object as a clone isn't really a solution, since that's fairly wasteful. The idea is to use the original. Also, if you save a bunch of rectangles in a collection (varray of shape_t), and then do a treat to get a rectangle back, does it have the attributes of the original rectangle, or only those of the shape_t plus new default rectangle attributes? Regards, -scott anderson "Welcome to Rivendell, Mr. Anderson..."
Post #114,805 by ChrisR 8/21/03 3:33:13 PM Reply	Quickly exhausting my sum total of PL/SQL knowledge :-) Also, if you save a bunch of rectangles in a collection (varray of shape_t), and then do a treat to get a rectangle back, does it have the attributes of the original rectangle, or only those of the shape_t plus new default rectangle attributes? From my limited tests, it does appear that the attributes from the collection are correctly maintained (although copy would seem to be the more appropriate term). Copying the object as a clone isn't really a solution, since that's fairly wasteful. The idea is to use the original. Can't help you there. A downcast operator that clones really isn't a downcast operator is it? :-) Speaking of cast, what about the CAST function. Appears to convert one type of collection to another. But I can't figure how to use it.
Post #114,812 by admin 8/21/03 4:29:32 PM Reply	Re: Quickly exhausting my sum total of PL/SQL knowledge :-) Only works on collections and built-ins. And in the case of a collection, CAST apparently needs to be used on a query. Regards, -scott anderson "Welcome to Rivendell, Mr. Anderson..."
Post #115,003 by ChrisR 8/22/03 7:37:20 PM Reply	Some other thoughts on TREAT I see that TREAT was not implemented in Oracle until release 2 of 9i - which is probably why the docs you have say it's not supported. Playing a bit more, I see that functions which return values can be used with the dot notation: i := TREAT(scribble(1) AS rectangle).getHeight(); -- this works TREAT(scribble(1) AS rectangle).setHeight(50); -- this doesn't compile I can't tell whether the function call does a copy, though I don't see why it would be different than what I had on the previous posts.
Post #115,023 by admin 8/22/03 9:59:26 PM Reply	I'll pass that on And as soon as I get 9.2 up on my box I'll start playing with it as well. Regards, -scott anderson "Welcome to Rivendell, Mr. Anderson..."
Post #114,859 by boxley 8/21/03 11:17:24 PM Reply	can you not bang out to .dat files in the OS? Unless and probably misunderstanding what you need temp data descripts of an object store useless perhaps knowledge in /tmp/foo if called suck /tmp/foo into memory and populate object floating config files. thanx, bill who still uses bc in scripts for math America, Love it or give it back questions, help? [link\|mailto:pappas@catholic.org\|email pappas at catholic.org]
Post #114,897 by admin 8/22/03 9:42:59 AM Reply	In-memory, transient. In other words, we're trying to do OO programming in PL/SQL, and we're being defeated by arbitrary restrictions that require the use of tables in conjunction with objects. Regards, -scott anderson "Welcome to Rivendell, Mr. Anderson..."

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