| Subject | Re: [IBDI] Subsets |
|---|---|
| Author | Jason Wharton |
| Post date | 2001-06-05T14:46:19Z |
It is also difficult to react to an update of the column values that are
ordered by.
Neither way is perfect. I was hoping to avoid the full complexity but since
you are willing to go there I suppose we can whip this horse into a bloody
pulp.
The times that I use a bookmark in this manner I have means to ensure that I
can always figure out what has happened to it. When a "delete" happens It is
either a change to a record such that it is filtered out of a result set or
if it is actually deleted I always have a separate log table which can be
referenced. So, I design systems where my bookmarks are always around (until
purged).
If you look in the normal place for a bookmark and don't find it then you
know to look in the logged place for it. Or, you know to drop off some of
the filter criteria to see what happened to if. At that point there are
different ways to get back to the position you wanted earlier. You could
fall back on a numerical based or just rely upon the values for the
bookmark.
The easiest way to accomplish this is to have a generation id to accompany a
bookmark. This way you can always find the original record in the system. If
you pull up a bookmark you can check its current generation id with the one
upon fetching it. If they are the same, take full confidence. If they are
different, then look to your logged table of changes. Triggers and stored
procedures can be designed to automate this easily. Triggers to maintain the
log table and stored procedures to return a record for a bookmark and
generation id, whether deleted, updated or still in original condition.
This way the only window for error is during purging of records which
shouldn't happen very often. Once a year or quarter or something like that.
FWIW,
Jason Wharton
CPS - Mesa AZ
http://www.ibobjects.com
ordered by.
Neither way is perfect. I was hoping to avoid the full complexity but since
you are willing to go there I suppose we can whip this horse into a bloody
pulp.
The times that I use a bookmark in this manner I have means to ensure that I
can always figure out what has happened to it. When a "delete" happens It is
either a change to a record such that it is filtered out of a result set or
if it is actually deleted I always have a separate log table which can be
referenced. So, I design systems where my bookmarks are always around (until
purged).
If you look in the normal place for a bookmark and don't find it then you
know to look in the logged place for it. Or, you know to drop off some of
the filter criteria to see what happened to if. At that point there are
different ways to get back to the position you wanted earlier. You could
fall back on a numerical based or just rely upon the values for the
bookmark.
The easiest way to accomplish this is to have a generation id to accompany a
bookmark. This way you can always find the original record in the system. If
you pull up a bookmark you can check its current generation id with the one
upon fetching it. If they are the same, take full confidence. If they are
different, then look to your logged table of changes. Triggers and stored
procedures can be designed to automate this easily. Triggers to maintain the
log table and stored procedures to return a record for a bookmark and
generation id, whether deleted, updated or still in original condition.
This way the only window for error is during purging of records which
shouldn't happen very often. Once a year or quarter or something like that.
FWIW,
Jason Wharton
CPS - Mesa AZ
http://www.ibobjects.com
----- Original Message -----
From: "Peter Morris" <pmorris@...>
To: <IBDI@yahoogroups.com>
Sent: Tuesday, June 05, 2001 9:20 AM
Subject: Re: [IBDI] Subsets
> > Bookmark is just my generic way of saying the information necessary to
> > identify a record on the server. If you have a key to a record then you
> have
> > the ability to get any information from that record on the server-side.
>
> Taking your earlier example of deleting records, what would then happen if
> the bookmark-record was deleted ?
>
> Pete
>
>
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