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 CONTROL OR DATA 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.
|17.||Define Data Store?|
|DataStore is a non-visual DataWindow control. DataStore used for Background processing, processing Embeded SQL and Distributed objects.
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.
We can use DataStore in the server application when we are developing a distributed application.
|18.||Which Data Source in the DataWindow painter is itself an object?|
|19.||What Data Sources do you know and how do you use them?|
|The Data Source determines how we select the data that will be used in the DW object. If the data for the DataWindow object is retrieved from a database, we may choose one of the following Data Sources:
Quick Select is a select from one or multiple tables that are joined through foreign keys and may include simple selection criteria which appear on the WHERE clause. We can only choose columns, selection criteria, and sorting. We cannot specify grouping before rows retrieved, include computed columns, or specify retrieval arguments.
SQL Select is an SQL Select statement from one or more tables in a relational database and may include selection criteria that appear on any of the possible Select statement clauses (can include selection criteria (WHERE clause), sorting criteria (ORDER BY clause), grouping criteria (GROUP BY and HAVING clauses), computed columns, one or more arguments to be supplied during execution.
Query is a predefined SQL Select statement, which must be previously constructed and saved as a Query object.
Stored Procedure indicates that the DataWindow will execute a Stored Procedure and display the data in the first result set. This Data Source only appears if the DBMS to which PowerBuilder is connected and which supports Stored Procedures. We can specify that the data for a DataWindow object is retrieved through a stored procedure if our DBMS supports Stored Procedures.
External is used when the data is not in the database and the DataWindow object will be populated from a script or data will be imported from a DDE application. If the data is not in the DB, we select External as the Data Source. This includes the following situations:
If the DataWindow object is populated from a script
If data is imported from a DDE application
If data is imported from an external file, such as a tab-separated text file (.TXT file) or a dBASE file (.DBF file).
Externalindicates that we have coded a script that supplies the DataWindow object with its data. We use this Data Source when the data is in a .TXT or .DBF file or obtained through DDE. We may also use it when we plan to obtain the data by embedding our own SQL Select statement in a script. With this Data Source the DataWindow object does not issue its own SQL statement. We specify the data columns and their types so that PB can build an appropriate
DataWindow object to hold the data. These columns make up the result set. In a script, we will need to tell PowerBuilder how to get data into the DataWindow in our application. Typically, we will import data during execution using a PowerScript Import function (such as ImportFile() and ImportString() or do some data manipulation and use the SetItem() function to populate the DataWindow.
|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.|