Oracle - Wrong default value FIX #34482

[SebastienPeillet]

FIX #34482
FIX #32401

Description

Default values are misreaded from all_tab_columns table.

Default values are retrieving from the data_default field in all_tab_columns table (see here).

And long story short :

• data_default is a long type column
• long is a type that can contains a lot of data, so data is readed in a "piecewise" mode (see qsql_ocispatial.cpp and oracle documentation)
• piecewise read mode concatenates the value piece by piece (for a single row), but after the first row the value is not cleared, so it concatenates the current default value with the previous one, etc

The solution is to clear values if piecewise mode is used.

We already test default values in test_provider_oracle.py :

    def testDefaultValue(self):
        self.assertEqual(self.source.defaultValue(1), NULL)
        self.assertEqual(self.source.defaultValue(2), "'qgis'")

I add self.assertEqual(self.source.defaultValue(3), "'qgis'") that is not tested yet. Without the PR changes, self.source.defaultValue(3) is equal to "qgisqgis" and not "qgis"

No backport before backporting #36654

[uclaros]

@SebastienPeillet @nyalldawson I am not quite sure what this change fixed or what piecewise is, but I am quite confident it is responsible for #42857 that I stumbled upon recently.

Right after clearing values:

QGIS/src/providers/oracle/ocispatial/qsql_ocispatial.cpp

Lines 3416 to 3417 in 642deb1

	values.clear();
	r = d->cols->readPiecewise( values, index );

values is accessed by index within readPiecewise() causing a crash:

QGIS/src/providers/oracle/ocispatial/qsql_ocispatial.cpp

Lines 1590 to 1605 in 642deb1

	if ( isStringField )
	{
	QString str = values.at( fieldNum + index ).toString();
	str += QString( reinterpret_cast<const QChar *>( col ), chunkSize / 2 );
	values[fieldNum + index] = str;
	fieldInf[fieldNum].ind = 0;
	}
	else
	{
	QByteArray ba = values.at( fieldNum + index ).toByteArray();
	int sz = ba.size();
	ba.resize( sz + chunkSize );
	memcpy( ba.data() + sz, reinterpret_cast<char *>( col ), chunkSize );
	values[fieldNum + index] = ba;
	fieldInf[fieldNum].ind = 0;
	}

I don't know what changed to force me to the piecewise codepath though, I've never had issues until this week!