Deleting Data
Class
RWDBDeleter is used to delete rows from database tables. A deleter is obtained by requesting one from a database table, and it may be supplied with an
RWDBCriterion to express a restriction on the rows to be deleted. You can express a restriction through a
where() method, just as with
RWDBSelector and
RWDBUpdater. The structure should be familiar by now:
int videoID = 1234;
RWDBTable purchases = myDbase.table("purchase");
RWDBDeleter deleter = purchases.deleter();
deleter.where(purchases["videoID"] == videoID); //1
deleter.execute(myConnection); //2
This example is equivalent to an SQL statement of this type:
DELETE FROM purchase WHERE videoID = 1234
It is executed on
//2, deleting the rows in the purchase table whose
videoID column contains the value
1234. As with
RWDBUpdater, the
where() call on
//2 is important. Omitting it would have caused all rows in the purchase table to be deleted. Executing a deleter without calling the
where() method, which assigns a criterion, causes all rows within the table to be deleted.
NOTE: Executing a deleter without first assigning a criterion causes all rows of the table to be deleted.
As with an updater, once a criterion has been assigned to a deleter using the
where() method, that criterion is retained. The
where() method can be called at anytime to set a new criterion, or it can be called with an empty criterion to clear the criterion. The considerations regarding results and connections for
RWDBInserter and
RWDBUpdater apply equally to
RWDBDeleter.
