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#include <iostream>
#include <map>
#include "test_helpers.hxx"
using namespace PGSTD;
using namespace pqxx;
// Example program for libpqxx. Modify the database, retaining transactional
// integrity using the transactor framework, and using lazy connections.
namespace
{
// Global list of converted year numbers and what they've been converted to
map<int,int> theConversions;
// Convert year to 4-digit format.
int To4Digits(int Y)
{
int Result = Y;
PQXX_CHECK(Y >= 0, "Negative year: " + to_string(Y));
if (Y < 70) Result += 2000;
else if (Y < 100) Result += 1900;
else PQXX_CHECK(Y >= 1970, "Unexpected year: " + to_string(Y));
return Result;
}
// Transaction definition for year-field update
class UpdateYears : public transactor<>
{
public:
UpdateYears() : transactor<>("YearUpdate") {}
// Transaction definition
void operator()(argument_type &T)
{
// First select all different years occurring in the table.
result R( T.exec("SELECT year FROM pqxxevents") );
// Note all different years currently occurring in the table, writing them
// and their correct mappings to m_Conversions
for (result::const_iterator r = R.begin(); r != R.end(); ++r)
{
int Y;
// Read year, and if it is non-null, note its converted value
if (r[0].to(Y))
m_Conversions[Y] = To4Digits(Y);
}
// For each occurring year, write converted date back to whereever it may
// occur in the table. Since we're in a transaction, any changes made by
// others at the same time will not affect us.
for (map<int,int>::const_iterator c = m_Conversions.begin();
c != m_Conversions.end();
++c)
T.exec("UPDATE pqxxevents "
"SET year=" + to_string(c->second) + " "
"WHERE year=" + to_string(c->first));
}
// Postprocessing code for successful execution
void on_commit()
{
// Report the conversions performed once the transaction has completed
// successfully. Do not report conversions occurring in unsuccessful
// attempts, as some of those may have been removed from the table by
// somebody else between our attempts.
// Even if this fails (eg. because we run out of memory), the actual
// database transaction will still have been performed.
theConversions = m_Conversions;
}
// Postprocessing code for aborted execution attempt
void on_abort(const char Reason[]) throw ()
{
try
{
// Notify user that the transaction attempt went wrong; we may retry.
cerr << "Transaction interrupted: " << Reason << endl;
}
catch (const exception &)
{
// Ignore any exceptions on cerr.
}
}
private:
// Local store of date conversions to be performed
map<int,int> m_Conversions;
};
void test_026(transaction_base &)
{
lazyconnection C;
{
nontransaction T(C);
test::create_pqxxevents(T);
T.commit();
}
// Perform (an instantiation of) the UpdateYears transactor we've defined
// in the code above. This is where the work gets done.
C.perform(UpdateYears());
// Just for fun, report the exact conversions performed. Note that this
// list will be accurate even if other people were modifying the database
// at the same time; this property was established through use of the
// transactor framework.
for (map<int,int>::const_iterator i = theConversions.begin();
i != theConversions.end();
++i)
cout << '\t' << i->first << "\t-> " << i->second << endl;
}
} // namespace
PQXX_REGISTER_TEST_NODB(test_026)
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