Difference between do-while, do-when, do-until and do-select in app engine.

Question

Hi can anyone please tell me the difference between do-while, do-when, do-until and do-select in app engine.
I read the peoplebooks, but i was not able to keep up with that.
I know like do-while is like WHILE loop in any programming language.
here my question starts. WHILE has a condition inside the parenthesis and it will check whether that condition is true or not. where do we have that condition in do-while(is it the where conditions inside the do-while)?
Please clarify me.
Thank you,
Bye.

Answer 1

Hello user609854,
Do-While
in simple words it is like, keep doing specified task , up to / when the condition is matching. once this is over, terminate the loop and come out. :)
If the Do While does not return any rows, the step is complete.
DoWhen - Select statement that allows subsequent actions to be executed if any rows of data are returned.i.e.when a particular conditions is matched like emplid='A2200' or may be a role based criteria etc
A Do When statement runs before any other actions in the step. If the Do When statement returns any rows,the next action is executed.
If the Do When conditions are not met, the remaining actions within that step are
not executed. Your program executes a Do When action only once when the owning step executes.
The only property that you can specify for the Do When action is the ReUse Statement property, which applies to all SQL-based actions.
Do-Until
Keep performing certain task , every time a particular task is being performed. its like keep doing task B until task A is accomplished.
A Do Until action is a Select statement that runs after each action when a step completes. Use aDoUntil action if you want the processing actions to execute at least once, and to execute over and over until a certain condition is true, such as until a Select statement returns some rows.You can also use a Do Until action to stop a Do Select action prematurely.
Do-Select
a) Select/Fetch : AE performs a Fetch statement for each iteration of the loop to get each row from the Select statement
b) Re-Select : For each Iteration , opens a cursor and fetches the first row. The cursor is reopen for each iteration. we put certain criteria by which the conditions should not match else this can be a deadlock
c) Restartable : This is same as ReSelect accept, Restartable flexibility.
We can restart this select/fetch as AE performs a checkpoint in the middle of the step. SQL in this mode,during restart will recognize where the previous run failed&where to restart processing.
Please Note: When AE is not set up for restartability, then commits are not controlled, monitored, or restricted by PeopleSoft Application Engine.
In Do Actions & Do Select we can specify ReUseStatement ~ SQL-based actions.
Please , let me know if this is fine with you.
SM Sachdeva