Async database parameter
Description
Allows you to perform asynchronous operations on your database
in PowerBuilder. If you have coded a RetrieveRow event for a DataWindow object or
report, you can cancel the current database retrieval operation
or start another (non-database) operation that does not use the
same database connection before the current operation completes. You
can also switch to another Windows process while the retrieval takes
place.
By default, PowerBuilder operates synchronously.
Controls
-
ASE, SYC SAP Adaptive
Server Enterprise -
DIR Sybase DirectConnect
-
I10 Informix
-
IN9 Informix
-
JDB JDBC
-
ODBC (if driver and back-end DBMS support this feature)
-
O90 Oracle9i
-
O10 Oracle 10g
-
ORA Oracle 11g
Syntax
|
1 |
Async=<span>value</span> |
|
Parameter |
Description |
|---|---|
|
value |
A value specifying synchronous or asynchronous
|
Default
Async=0
Usage
Enabling asynchronous operation in PowerBuilder is useful when
you are executing a complex SQL statement
that takes several minutes to return results. If the Async parameter
is set to 1, you can do either of the following while the SQL statement is executing:
-
Work in another window
-
Cancel the statement before it retrieves the first
row of data
When to set Async
If you are communicating with the database in code, you can
reset the Async value at any time before or after the Transaction
object has connected to the database.
How data is retrieved
When you retrieve data in a DataWindow object or report, the following
steps occur in order:
-
The database server
compiles and executes the SQL statement. -
PowerBuilder retrieves (fetches) the first row of
data. -
PowerBuilder retrieves each subsequent row of data.
What happens before the first row is retrieved
While the server is compiling and executing the SQL statement and before PowerBuilder retrieves
the first row of data, you must have done both of
the following to enable asynchronous operation (allowing you to
cancel the current operation before it retrieves the first row of
data):
-
Coded a RetrieveRow
event for the DataWindow object or report (the code can contain only a
comment) -
Set the Async parameter to 1
What happens after the first row is retrieved
After the first row of data is retrieved and between subsequent
row fetches, you must have done only the following to enable asynchronous
operation:
-
Coded a RetrieveRow
event for the DataWindow object or report
After the first row is retrieved, PowerBuilder operates asynchronously without your
having to set the Async parameter to 1, so you can cancel
the current operation anytime after it retrieves the first row of
data. Therefore, the Async parameter has no effect in PowerBuilder after
the first row of data is retrieved.
Examples
Example 1
To enable asynchronous operation:
-
Database profile
Select the Asynchronous check box on the Transaction page
in the Database Profile Setup dialog box. -
Application
Type the following in code:
1SQLCA.DbParameter="Async=1"
Example 2
You can set the Async and DBGetTime parameters in a single statement.
DBGetTime specifies the number of seconds you want PowerBuilder to
wait for a response from the DBMS when you retrieve rows in a DataWindow object or
report. To enable asynchronous operation and set the DBGetTime parameter
to 20 seconds:
-
Database
profileSelect the Asynchronous check box and type 20 in the Number
Of Seconds To Wait box on the Transaction page in the Database Profile
Setup dialog box. -
Application
Type the following in code:
1SQLCA.DbParameter="Async=1,DBGetTime=20"