OpenEdge Data Management: DataServer for Microsoft SQL Server

Error handling
Error handling
One common data entry error is attempting to add a duplicate record; that is, trying to create a
record using a unique key that already exists in the database. Suppose, for example, that a user
tries to add a customer with custnum = 1 (where custnum is a unique key), but a customer
record with this custnum value already exists. The attempt fails and an error is generated.
When this type of error occurs, ABL run time engine tries to resolve it by working back through
the procedure, looking at each block header until the closest block with the error-handling
property is found, and then undoing and retrying the block. (See OpenEdge Getting Started:
ABL Essentials for more information about error handling.) However, because the DataServer
is accessing a non-OpenEdge data source, duplicate-key errors can not be detected until the end
of a transaction block. Therefore, if an error occurs in a subtransaction, it is not detected until
the end of the entire transaction block and default error handling must be performed for the
entire transaction block.
The following example illustrates OpenEdge database and DataServer error handling:
rep-blk:
REPEAT:
PROMPT-FOR customer.custnum. /* User input */
FIND customer USING custnum NO-ERROR.
IF AVAILABLE customer THEN
UPDATE customer.custnum customer.name customer.state. /* User input */
do-blk:
DO ON ERROR UNDO do-blk, RETRY do-blk:
FIND state WHERE st.state EQ customer.state.
DISPLAY state.
SET state. /* User input */
END.
END.
This procedure displays the following screen, in which the user is prompted to enter data into
the custnum field and then the state field:
The
OpenEdge
database
prompts for
the state
abbreviation.
Suppose that the user enters an existing state (for example, NH) while ABL is processing the DO
block. When this duplicate-key entry occurs for an OpenEdge database, ABL returns control to
the DO block, displays a message that the record exists, and reprompts the user for a state
abbreviation.
However, with the DataServer, if a duplicate key entry occurs in the DO block, ABL returns
control to the REPEAT block rather than the DO block. As a result, the procedure reprompts the
user for a customer number after the inner transaction completes:
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