OpenEdge Data Management: DataServer for Microsoft SQL Server

Chapter 2: Initial Programming Considerations
r-code
r-code is generated when an ABL procedure is compiled. The compiled r-code is
portable across user interfaces. For example, r-code that you compile on Sun Solaris
can run on any other UNIX system (character user interface).
r-code is not portable across Window systems; that is, r-code compiled for a character
application will not run on Windows and r-code compiled for Windows will not run on a
character user interface.
r-code is also not portable among database management systems. ABL generates
calls that are specific to a database. For example:
• Code that you compile for a database named sports will not run with a database
named mysports.
• Code that you compile for MS SQL Server will not run on an OpenEdge database.
Prior to OpenEdge Version 11, r-code stored the physical position of a database
column. r-code was not compatible with the server schema if the position of a column
changed on the server. In Version 11, r-code stores a logical identifier for the physical
position of a database column. Therefore, in OpenEdge 11, column positions in the
server table can be rearranged without the need to recompile.
See OpenEdge Deployment: Managing ABL Applications for more details on r-code
portability.
The size of r-code grows significantly when you compile procedures against a MS SQL
Server data source as compared to compiling against an OpenEdge database. The
r-code for a DataServer application contains as text portions of SQL statements that
the DataServer passes to the data source.
FOR statements
FOR FIRST and FOR LAST statements that cause the DataServer to sort data before
returning it to the client behave differently when returning data from a MS SQL Server
data source than when returning data from an OpenEdge database. The data source
might not sort data like the OpenEdge database does, so the order in which records
return might differ. In addition, the server-side result set is limited to a single record to
improve performance.
Features and language differences
The DataServer supplies you with complete ABL functionality when accessing MS SQL
Server data sources. Many ABL language elements (statements, functions, and so
forth) and Data Dictionary features work the same whether your application accesses
a data source through the DataServer or an OpenEdge database.
Use the DBRESTRICTIONS function to find out which OpenEdge features your MS SQL
Server data source does not support. For the DataServer for MS SQL Server,
DBRESTRICTIONS can return SETUSERID and COUNT–OF. In certain circumstances, it can
return additional values. For example, it can return READ–ONLY if you connect to the
schema holder in read-only mode. See the “DBRESTRICTIONS function” reference
entry in OpenEdge Development: ABL Reference for information on syntax.
116 OpenEdge Data Management: DataServer for Microsoft SQL Server