PowerBuilder Interview Question and Answers

16. Define DataWindow buffers?
When data is retrieved from the databse by using retrieve() function, it is retrieved into the Primary Buffer and it is the content of this buffer that are displayed in the datawindow.
Powerbuilder always displays the data in datawindow control from the Primary Buffer. Data from other buffers are not visible to the user.

When user modifies a row in the DataWindow the row in the Primary Buffer is modified and the original value is copied into the Original Buffer from the Primary Buffer. Copies data only when the user modify the row for the first time.

When the user deletes a row with the DeleteRow() function, rows are transferred from Primary Buffer to Deleted Buffer.

When rows are filtered using the SetFilter() function, the filtered rows are display in the DataWindow and don’t match the filterd conditions are moved to the Filtered Buffer.

Edit DataWindow Control has one edit control. It contains the current column’s data. When the user modify the data in a column modify data is copied in Edit Control Buffer. The modify data on the screen and the content of the Edit Control are same. But the value in the Primary Buffer has the old data.
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17. Define Data Store?
  DataStore is a non-visual DataWindow control. DataStore used for Background processing, processing Embeded SQL and Distributed objects.
Background Processing:
Sometimes we use multiple DataWindow control on the screen to display one single report. But those DataWindows are not usable for printing. So we use hidden DataWindow control for printing.

Processing Embedded SQL:
Lot of times we need to use embedded SQL to check whether a particular record is existing in the databse or not. So we can check for the existing record using DataStore.

Distrubuted Objects:
We can use DataStore in the server application when we are developing a distributed application.
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18. Which Data Source in the DataWindow painter is itself an object?
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19. When powerbuilder retrieves data from the database what status will be occurred?
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20. Under what circumstances will PowerBuilder automatically join tables that you select in the Select painter?
  If we select tables that have one or more columns with identical names, the Select painter automatically displays the join, assuming equality between the two columns.
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