Programming logic, passing data from a page to another

Question

Hi,
I just began with developing with APEX 4.1.1, and I think I don't get how I should use it efficiently, I am more used to C-like programming.
I have a table which contains the state of some electricity meters taken at some non-regularly spaced dates. I want to make a chart of the electricity consumption, e.g for each month. This (I think) implies that the application must do that (I used this logic for the same application made with php and sqlite and it worked):
- User chooses a meter
- Application tells him the available range of dates and the mean interval between measurements
- User chooses the range of dates and the interval
- Application verifies that the range of dates is valid (not outside the real data)
- Interpolate the state of the meters at the requested regular interval
- Calculate the consumption for each interval (simply a difference)
- Draw the chart
For now, I created some procedures which should pass a custom data type containing all the meta-data about the chart and a PL/SQL table containing the actual data to be charted, but I'm stuck at the point of interacting with the user (meaning writing the output of the procedures on a page and passing them to the next procedure and also charting that pl/sql table).
Maybe should I create a temporary table ? But of what I read, this is a "real" table stored on the disk, and I just need this data once (and it is a small dataset, at most 20 points or so) for drawing a chart. This table should also be specific to the chart currently being created, it could happen that the same user or different users make multiple charts at the same time (like in two firefox tabs).
I hope my post is not too confused..
Ben

Answer 1

940065 wrote:
Hi,
I just began with developing with APEX 4.1.1, and I think I don't get how I should use it efficiently, I am more used to C-like programming.Welcome to the forum: please read the FAQ and forum sticky threads (if you haven't done so already), and update your profile with a real handle instead of "940065".
APEX is intended for the development of database centric applications. It's a physical implementation of Tom Kyte's philosophy of database application development—possibly replacing Java with JavaScript ;-) .
To use it efficiently you need to stop thinking procedurally in C-like terms and think in terms of the set operations that SQL uses effectively.
I have a table which contains the state of some electricity meters taken at some non-regularly spaced dates. I want to make a chart of the electricity consumption, e.g for each month. This (I think) implies that the application must do that (I used this logic for the same application made with php and sqlite and it worked):
- User chooses a meter
- Application tells him the available range of dates and the mean interval between measurements
- User chooses the range of dates and the interval
- Application verifies that the range of dates is valid (not outside the real data)
- Interpolate the state of the meters at the requested regular interval
- Calculate the consumption for each interval (simply a difference)
- Draw the chart
For now, I created some procedures which should pass a custom data type containing all the meta-data about the chart and a PL/SQL table containing the actual data to be charted,
but I'm stuck at the point of interacting with the user (meaning writing the output of the procedures on a page and passing them to the next procedure and also charting that pl/sql table).It seems that you don't really get APEX yet: have you read the introductory documentation and taken the <i>Oracle® Database 2 Day + Application Express Developer's Guide</i> tutorial in order to understand basic APEX techniques and terminology?
You should be aiming to collect and validate the required parameters in APEX session state values and use the built-in charting capability with SQL data sources that use these parameter values in query predicates.
If you really can't generate the chart series from queries run on the original table, generate the chart data using an APEX collection rather than a "PL/SQL table" (preferred terminology is "collection type", but it's even better to specifically say "associative array", "nested table" or "varying array") or temporary database table.
Maybe should I create a temporary table ? But of what I read, this is a "real" table stored on the disk, and I just need this data once (and it is a small dataset, at most 20 points or so) for drawing a chart. This table should also be specific to the chart currently being created, it could happen that the same user or different users make multiple charts at the same time (like in two firefox tabs).Temporary tables are rarely required in any Oracle application, but standard Oracle Global Temporary Tables are database-session specific and so have no concurrency issues. However there are issues when using them in APEX, so APEX collections are the preferred method for temporary, session-based storage.