Date: 2004-05-05T09:03:30
Editor: 194.175.229.106 <>
Wiki: DB Torque Wiki
Page: FrequentlyAskedQuestions
URL: http://wiki.apache.org/db-torque/FrequentlyAskedQuestions
no comment
Change Log:
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@@ -247,3 +247,26 @@
While coding your own transactions, make sure that the Database connection is
released at the end. This is ensured in the above code because either
Transaction.commit() or Transaction.rollback() are called, both of which release the
database connection. Note that Transaction.safeRollback() does not release the
database connection, so replacing Transaction.rollback() by transaction.safeRollback()
in the above code would lead to the leakage of database connections if the transaction
fails.
-- Thomas Fischer
+
+== How can I count datasets in a table ? ==
+
+Suppose one wants to execute a SQL-statement like "select count(*) from employee
where name='james'".
+
+'''Answer:''' This query can be executed using the following code (assuming the
employee Table has at least two Columns: "NAME" and "ID", where ID is the primary key,
and the Peer class to the employee Table is EmployeePeer (sorry the link does not work
but I don't know how to get rid of it)):
+{{{
+int numberOfRecords;
+{
+ org.apache.torque.util.Criteria criteria = new org.apache.torque.util.Criteria();
+ criteria.add(EmployeePeer.NAME, "james");
+ criteria.addSelectColumn("COUNT(" + EmployeePeer.ID + ")");
+ java.util.List result = EmployeePeer.doSelectVillageRecords(criteria);
+ com.workingdogs.village.Record record = (com.workingdogs.village.Record)
result.get(0);
+ numberOfRecords = record.getValue(1).asInt();
+}
+}}}
+
+I don't know which columns should be used in addSelectColumn (and if it makes a
difference which one is used), but I presume using the primary key is fine. Note that
addSelectColumn("count(*)") does not work.
+
+The answer was put together from articles by Scott Eade and Tulsi Das on the Torque
Users Mailing List.
+
+-- Thomas Fischer
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