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Date: Mon, 06 Apr 2009 20:59:05 -0700
From: Bryan Pendleton <bpendleton@amberpoint.com>
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To: Derby Dev <derby-dev@db.apache.org>
Subject: jdbc:default:connection and data modification statements (DERBY-2487)
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In my current investigation of DERBY-2487, I've been working with
jdbc:default:connection, and mostly I've been successful.

However, in some of my tests, I encounter an error:

java.sql.SQLException: No current connection.
         at org.apache.derby.impl.jdbc.SQLExceptionFactory.getSQLException(SQLExceptionFactory.java:45)
         at org.apache.derby.impl.jdbc.Util.newEmbedSQLException(Util.java:87)
         at org.apache.derby.impl.jdbc.Util.newEmbedSQLException(Util.java:103)
         at org.apache.derby.impl.jdbc.Util.noCurrentConnection(Util.java:207)
         at org.apache.derby.impl.jdbc.EmbedConnectionContext.getNestedConnection(EmbedConnectionContext.java:113)
         at org.apache.derby.jdbc.InternalDriver.connect(InternalDriver.java:176)

The crucial aspect of this error appears to be this code in EmbedConnectionContext:

             if ((sc == null) || (sc.getSQLAllowed() < org.apache.derby.catalog.types.RoutineAliasInfo.MODIFIES_SQL_DATA))
                 throw Util.noCurrentConnection();

Can anybody help me understand the logic behind this code?

Alternatively, here's the problem I'm trying to solve:

At the completion of statement execution, I'm gathering the runtime
statistics regarding the statement, and I want to store that data
into the XPLAIN tables in the database. To do this, I've been
grabbing a connection using code like this:

         InternalDriver id = InternalDriver.activeDriver();
         if (id != null) {
             Connection conn = id.connect("jdbc:default:connection", null);
             if (conn != null)
                 return conn;
         }

This generally succeeds in getting me a connection with which I can
execute INSERT statements into the XPLAIN tables. However, in scenarios
such as the following:

         at org.apache.derby.jdbc.InternalDriver.connect(InternalDriver.java:176)
         at org.apache.derby.impl.sql.execute.xplain.XPLAINSystemTableVisitor.getDefaultConn(XPLAINSystemTableVisitor.java:2789)
         at 
org.apache.derby.impl.sql.execute.xplain.XPLAINSystemTableVisitor.addStmtDescriptorsToSystemCatalog(XPLAINSystemTableVisitor.java:2805)
         at org.apache.derby.impl.sql.execute.xplain.XPLAINSystemTableVisitor.doXPLAIN(XPLAINSystemTableVisitor.java:2730)
         at org.apache.derby.impl.sql.execute.NoRowsResultSetImpl.close(NoRowsResultSetImpl.java:375)
         at org.apache.derby.impl.sql.execute.InsertResultSet.cleanUp(InsertResultSet.java:2026)
         at org.apache.derby.impl.sql.execute.InsertResultSet.open(InsertResultSet.java:512)
         at org.apache.derby.impl.sql.GenericPreparedStatement.executeStmt(GenericPreparedStatement.java:416)

I get the "No current connection" thrown from the InternalDriver.connect
method because my current statement context is not allowing a nested
connection to be opened.

Is there a better technique for getting an internal connection to use
for storing the statistics data into the user tables?

thanks,

bryan