Using stored procedures to update the database
Updates to the database can be performed using stored procedures.
Why use stored procedures?
The DataWindow control submits updates to the database by
dynamically generating INSERT, DELETE,
and UPDATE SQL statements
after determining the status of each row in the DataWindow object.
You can also define procedural SQL statements
in a stored procedure for use by all applications accessing a database.
Using stored procedures to perform database updates allows you to
enhance database security, integrity, and performance. Since stored
procedures provide for conditional execution, you can also use them
to enforce additional business rules.
Updating using stored procedures
The Stored Procedure Update dialog box only allows you to
associate an existing stored procedure with your DataWindow object.
The stored procedure must have been previously defined in the database.
To use stored procedures to update the database
-
In the DataWindow painter, select Rows>Stored
Procedure Update to display the Stored Procedure Update dialog box. -
Select the tab for the SQL update
method (Delete, Insert, or Update) with which you want to associate
a stored procedure. -
Click the Procedure button, select the stored
procedure you want to be executed when the SQL update
method is generated, and click OK.The parameters used in the stored procedure are displayed
in the Argument Name list in the order they are defined in the procedure.
Column Name lists the columns used in your DataWindow object. -
Associate a column in the DataWindow object or
an expression with a procedure parameter.If a stored procedure uses parameters that are not matched
to column names, you can substitute the value from a DataWindow
object computed field or expression.
Matching a column to a procedure parameter You must be careful to correctly match a column in the DataWindow object
to a procedure parameter, since PowerBuilder is only able to verify that
datatypes match. -
If the parameter is to receive a column value,
indicate whether the parameter will receive the updated column value
entered via the DataWindow object or retain the original column
value from the database.Typically, you select Use Original when the parameter is used
in a WHERE clause in an UPDATE or DELETE SQL statement. If you do not select
Use Original, the parameter will use the new value entered for that
column. Typically, you would use the new value when the parameter
is used in an INSERT or UPDATE SQL statement.
What happens when the stored procedure is executed
The stored procedure you associate with a SQL update method in the Stored Procedure
Update dialog box is executed when the DataWindow control calls the Update function.
The DataWindow control examines the table in the DataWindow object,
determines the appropriate SQL statement
for each row, and submits the appropriate stored procedure (as defined
in the Stored Procedure Update dialog box) with the appropriate
column values substituted for the procedure arguments.
If a stored procedure for a particular SQL update
method is not defined, the DataWindow control submits the appropriate SQL syntax in the same manner it
always has.
Return values from procedures cannot be handled by the DataWindow
control. The Update function returns 1 if it
succeeds and -1 if an error occurs. Additional information is returned
to SQLCA.
Using Describe and Modify
You can use the DataWindow Describe and Modify functions
to access DataWindow property values including the stored procedures
associated with a DataWindow object. For information, see the DataWindow
object property Table.property in the DataWindow Reference
.
Restrictions on the use of Modify
Since a database driver can only report stored procedure names
and parameter names and position, it cannot verify that changes
made to stored procedures are valid. Consequently, if you use Modify to
change a stored procedure, be careful that you do not inadvertently
introduce changes into the database.
In addition, using Modify to enable a DataWindow
object to use stored procedures to update the database when it is
not already using stored procedures requires that the type qualifier
be specified first. Calling the type qualifier ensures that internal
structures are built before subsequent calls to Modify.
If a new method or method arguments are specified without a preceding definition
of type, Modify fails.