How the DataWindow control updates the database
When updating the database, the DataWindow control determines
the type of SQL statements to generate by looking at the status
of each of the rows in the DataWindow buffers.
There are four DataWindow item statuses, two of which apply
only to rows:
|
Status |
Applies to |
||
|---|---|---|---|
|
PowerBuilder name |
Web DataWindow name |
Numeric value |
|
|
New! |
New |
2 |
Rows |
|
NewModified! |
NewModified |
3 |
Rows |
|
NotModified! |
NotModified |
0 |
Rows and columns |
|
DataModified! |
DataModified |
1 |
Rows and columns |
Named or numeric constants
The constants shown in the table are used differently in each
environment:
PowerBuilder
The named values are values of the enumerated datatype dwItemStatus.
You must use the named values, which end in an exclamation point.
Web DataWindow
You can use a string value with or without the exclamation
point
Web ActiveX
Named values are not defined; use the numeric values.
This discussion uses the PowerBuilder names.
How statuses are set
When data is retrieved
When data is retrieved into a DataWindow, all rows and columns
initially have a status of NotModified!.
After data has changed in a column in a particular row, either
because the user changed the data or the data was changed programmatically,
such as through the SetItem method, the column status for that column
changes to DataModified!. Once the status for any column in a retrieved
row changes to DataModified!, the row status also changes to DataModified!.
When rows are inserted
When a row is inserted into a DataWindow, it initially has
a row status of New!, and all columns in that row initially have
a column status of NotModified!. After data has changed in a column
in the row, either because the user changed the data or the data
was changed programmatically, such as through the SetItem method,
the column status changes to DataModified!. Once the status for
any column in the inserted row changes to DataModified!, the row
status changes to NewModified!.
When a DataWindow column has a default value, the column’s
status does not change to DataModified! until the user makes at
least one actual change to a column in that row.
When Update is called
For rows in the Primary and Filter buffers
When the Update method is called, the DataWindow control generates SQL INSERT and UPDATE statements
for rows in the Primary and/or Filter buffers based upon
the following row statuses:
|
Row status |
SQL statement |
|---|---|
|
NewModified! |
INSERT |
|
DataModified! |
UPDATE |
A column is included in an UPDATE statement only if the following
two conditions are met:
-
The
column is on the updatable column list maintained by the DataWindow
objectFor more information about setting the update
characteristics of the DataWindow object, see the PowerBuilder
Users Guide. -
The column has a column status of DataModified!
The DataWindow control includes all columns in INSERT statements
it generates. If a column has no value, the DataWindow attempts
to insert a NULL. This causes a database error if the database does
not allow NULLs in that column.
For rows in the Delete buffer
The DataWindow control generates SQL DELETE statements for
any rows that were moved into the Delete buffer using the DeleteRow
method. (But if a row has a row status of New! or NewModified! before
DeleteRow is called, no DELETE statement is issued for that row.)