OpenEdge Data Management: DataServer for Microsoft SQL Server

Initial Programming Considerations
Cursors
2–48
A cursor is like a pointer that points to consecutive records in a table. The ABL uses cursors to
keep track of where it is in a table; for example, when it processes FOR EACH statements. Suppose
that you are reading records from the customer table using the custnum index, and your current
record is customer number 50. This means that ABL has a cursor positioned at custnum 50.
Note that ABL maintains cursor positioning across queries.
The DataServer allows applications that access MS SQL Server data sources to imitate
OpenEdge cursor behavior for FIND cursors. FOR EACH and OPEN QUERY statements do not retain
cursor position across other queries or against a FIND statement.
This section discusses the following cursor-related activities:
• Forward and backward scrolling
• Block cursors
For details about firehose and fast forward-only cursors, see the “Firehose and Fast
Forward-Only Cursors” section on page 4–5.
Forward and backward scrolling
A query is scrolling if you specify SCROLLING in the DEFINE QUERY statement or if you define a
browse for the query. You can use the REPOSITION statement to change your current position
with the result set. For a non-scrolling query, the DataServer allows you to only move
sequentially forward through the rows by using the FIRST and options of the GET statement.
Scrolling basically means that the result set is cached on the client for backward and forward
scrolling.
With the DataServer, forward and backward scrolling works with a MS SQL Server just as it
does with an OpenEdge database except when the data source fails to find a record. In ABL, the
cursor position can change after a failed search; however, with the DataServer, a failed search
does not affect the cursor. For example, if a cursor is positioned at custnum 50 and a request for
the next customer from an OpenEdge table fails, the cursor moves to the next sequential record
beyond custnum 50. The same failed request from a data source leaves the cursor at custnum 50.
Your DataServer applications should not assume a certain cursor position after a failed find.
You can, however, still use the AVAILABLE function to determine whether a record is available.
The AVAILABLE function behaves consistently whether it accesses an OpenEdge database or a
MS SQL Server data source.