Next/Previous Record: how APEX does it
It’s not a common requirement in my experience, but it does come up every now and then: a customer is happy with a simple Report + Form but when they open a record, they want to be able to make their changes and go to the “next” record in one button click, instead of having to go back to the report and select the other record.
In the Sample Database Application, page 29 (Order Details) implements “Next” and “Previous” buttons which allow the user to save and open another record in one action.
These buttons are implemented using a legacy Form Pagination process. This process sets some hidden items (
P29_ORDER_ID_COUNT) based on a query on a specified table (
DEMO_ORDERS) with a specified unique identifier (
ORDER_ID) associated with a primary key item (
P29_ORDER_ID). The process requires a navigation order, specified by one or two columns (
ORDER_ID, in this instance) in order to know what would the “next” and “previous” records be. If there is no next or previous record is found, the buttons are hidden.
When the page is submitted, the Next and Previous buttons submit a request (
GET_PREVIOUS_ORDER_ID, respectively). After the ApplyMRU process has run, one of the relevant Branches will redirect the client back to the same page (p29) and set
P29_ORDER_ID to either
&P29_ORDER_ID_PREV. which causes the page to load the relevant record.
Some things to note with this approach:
- The legacy Form Pagination process is limited to a maximum 2 columns for the uniqueness constraint, and 2 columns for the navigation order.
- The navigation order of records will not match any custom sort order or filtering the user might have used on the report; so after the user opens the “first record” in the report, the form will not necessarily navigate to the “next record” that they might expect.
- The Next / Previous record IDs are queried when the page is initially loaded, so if anything has changed prior to the user clicking “Next” or “Previous”, it’s possible the user will inadvertently be directed to a record that is not actually “next” or “previous” to the record as it is now.
In the worst case, if someone had deleted a record, the page would show “record not found”.
In a perhaps less problematic case, if someone else has just inserted a new record with a unique identifier that happens to fall between the user’s previous record and the record they are navigating to, the user will effectively “skip over” the newly inserted record and might be led to believe it doesn’t exist.
- For large datasets there may be a performance penalty whenever each user loads the form since the page must issue additional queries to find the IDs for the “previous smaller” and “next larger” record, as well as to get the total number of records, and the position in the overall dataset of the current record (so it can set the “count” item to something like “8 of 10”). This involves the execution of a second query (in addition to the original query which gathered the data for the record being viewed).
These are not necessarily insurmountable or showstopping issues but should be kept in mind for forms using this approach.
With the new APEX Form feature, the above approach can still be used in much the same way – the attribute settings are a little different.
The page has a process before header of type Form – Initialization. This process has the following optional settings: Next Primary Key Item(s), Previous Primary Key Item(s), and Current Row/Total Item. To use this feature you must first create items (usually hidden) and then set these attributes to the item names.
Note that the Next / Previous Primary Key Item(s) attributes accept a comma-delimited list of items which allows them to support a compound key; I haven’t tested it but I expect this means it can support more than 2 columns.
The form will automatically populate these hidden items with the Order ID of the next and previous record, and will set the Current Row/Total Item to something like “8 of 10”. You can then use these items how you wish, e.g. as per the legacy pagination scheme, add the “Next” and “Previous” buttons, and create the navigation Branches to open the form with the relevant records.
To control the navigation order, you must set the Order By attribute on the form region. If this is not set, the navigation order is essentially unpredictable (APEX uses
null as the sort order).
Same as the legacy pagination process, the form executes two queries: one to load the data for the form, and a second to gather the Next, Previous, Position and Count for the record, using SQL like this (I’ve simplified it a bit):
select i.* from ( select ORDER_ID, CUSTOMER_ID, ORDER_TOTAL, ... lead(ORDER_ID,1) over (order by ORDER_ID) as APX$NEXT_1, lag(ORDER_ID,1) over (order by ORDER_ID) as APX$PREV_1, row_number() over (order by ORDER_ID) as APX$ROWN, count(*) over () as APX$TOTAL from ( (select /*+ qb_name(apex$inner) */ d.ORDER_ID, d.CUSTOMER_ID, d.ORDER_TOTAL, ... from (select x.* from DEMO_ORDERS x) d )) i ) i where 1=1 and ORDER_ID=:apex$f1
It should be noted that the comments above about how concurrent record inserts and deletes by other users, and about report filters and sorting, also apply to the new form process.
In the past I built a system where it was important that the “Next” / “Previous” buttons should allow the user to navigate up and down the records exactly as shown in the report, respecting user-entered filters and sort order. The approach I took was to gather the IDs into a collection and pass this to the form when the user opened a record. I described the implementation and limitations of this approach in an older blog post which I expect still works today: Next/Previous buttons from Interactive Report results