Estimated row count

Question

hello
i used estimatedrowcount on several occasions in my application to hide and show certain parts of the screen (normally in EL expressions)
why is it called ESTIMATED and not EXACT. Of course, there is a reason why i ask,
sometimes and in certain pages in which i add new row, it is not also the case that the value of EstimatedRowcount is always updated when a new row is inserted. Also what if another use is adding rows through the same page but from a different browser (different instance of the same applications).
In other words, when does the framework issues SELECT count() on the page to reflect an updated SELECT count().
In certain situation , i had to create VO in order to make sure that i control that the count() is specifically calculated when i need since i noticed that the default EstimatedRowCount does not always give the expected result and henceforth, could be unwise to depend on it to control the logic
rgds
ammar sajdi
Amman jordan

Answer 1

You are right, the estimated row count does not query the database every time you call the method. It just is designed to give you the estimated row count in the context of the "current query" of the VO. So, you perform a query. After the query is performed, the table binding, for example, calls the getEstimatedRowCount() method to determine how many rows are to be expected (keep in mind that probably not all rows are fetched at once after the query). Nothing wrong with that. The ViewObject is executed, 20 rows are fetched, the estimated row count tells the binding that there are 100 rows in the result. If then another user inserts a new row, then that typically will have no effect on the 100 rows, meaning you won't get 101 rows at a sudden. If you scroll through the result set, you will get the 100 rows. In order to get 101 rows, you will need to re-execute the query. Then the table binding will get the estimated row count and it will be 101.
As soon as the fetch is complete, meaning that all rows are fetched from the database and are in memory, then getEstimatedRowCount() no longer accesses the database (why should it?!) but just returns the count of fetched rows. Of course, taking into account any unposted rows that you may have created.
If you really want the row count from the database, why don't you just call getQueryHitCount()? Why must it be getEstimatedRowCount()?!
Sascha