OpenEdge Data Management: DataServer for Microsoft SQL Server

Chapter 2: Initial Programming Considerations
Record creation
Record creation is handled differently for OpenEdge databases and MS SQL Server
data sources accessed through the DataServer. The difference occurs because ABL
code run against an OpenEdge database follows different record-scoping rules than
ABL code run against a MS SQL Server data source.
Records are scoped to the outermost block in which they are used, or the smallest
enclosing block that encompasses all references to a record. In the absence of
enclosing blocks, a record is scoped to the procedure block. Outside of record scope,
a buffer associated with a record is cleared by ABL.
The OpenEdge database writes a record to the database after all its indexed columns
are assigned. The MS SQL Server DataServer writes records or record changes out to
the database at the end of record scope or at the end of a transaction boundary within
that record scope. For this reason, the duration of record locks can vary between
OpenEdge and a MS SQL Server data source since the record lock will be held from
the time of the write until the end of a transaction.
While both OpenEdge and MS SQL Server data sources both commit changes at a
transaction boundary, OpenEdge is capable of downgrading the lock on a record within
scope after a commit boundary has been traversed. A MS SQL Server data source
drops all record locks at the end of a transaction. See the “Transaction scoping and
buffer management” section on page 100 for more information.
The following ABL statements will force a physical database write to a MS SQL Server
data source before the end of a transaction block or the end of record scope:
• RELEASE
• VALIDATE
• RECID/ROWID
While these statements can change lock status and force a write, they have no affect
on transaction scope. Locks will be held from the time of the write until the time of a
commit or rollback. For the RELEASE statement, the record is released from its buffer
but is inaccessible and still locked awaiting a transaction boundary. After a RELEASE, a
record would need to be reread in order to refill buffer content. The OpenEdge
database waits for all the key values to be assigned or for the end of record scope to
write a record regardless of the outcome of a VALIDATE statement. The MS SQL Server
DataServer writes a record at the time of the VALIDATE since a write is required in order
to resolve the integrity of a record within the MS SQL Server data source. OpenEdge
can assign a RECID or ROWID without writing a record. For a MS SQL Server data
source, the generation of RECID and ROWID are contingent on a record write in order to
produce its value.
The availability of database changes is dependent on when the record is written. The
user writing the record can read back the in-memory copy of the record as soon as it
has been written out to the database. Another user trying to access the same record
may or may not see the changes written to the database, depending on the transaction
isolation level of the foreign data source. While OpenEdge will show other users
records modified but not yet committed, a MS SQL Server data source will not report
on the state of record content until a transaction boundary has been traversed.
Therefore, while OpenEdge might indicate that a record already exists or has certain
content before another user has committed such changes, a MS SQL Server data
source will report that the record is in use and block access until the transaction is
complete. The code fragments in this section illustrate these differences.
90 OpenEdge Data Management: DataServer for Microsoft SQL Server