Retrieve auto-value for ODBC fields.

Introduce a static function returning the value called from
qMakeFieldInfo(SQLHANDLE). The field is currently only populated
when executing a query. Populating it from QODBCDriver::record()
would require executing a dummy query, which is problematic since
QSqlField does not have any provisions for delayed evaluation.
Document the limitation.

Task-number: QTBUG-39388
Change-Id: Ib2d2f2653b8b757389f627142c61c13a117fef72
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@digia.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@theqtcompany.com>

src/sql/drivers/odbc/qsql_odbc.cpp

@@ -579,6 +579,19 @@ static QVariant qGetBigIntData(SQLHANDLE hStmt, int column, bool isSigned = true
         return quint64(lngbuf);
 }
 
+static bool isAutoValue(const SQLHANDLE hStmt, int column)
+{
+    SQLLEN nNumericAttribute = 0; // Check for auto-increment
+    const SQLRETURN r = ::SQLColAttribute(hStmt, column + 1, SQL_DESC_AUTO_UNIQUE_VALUE,
+                                          0, 0, 0, &nNumericAttribute);
+    if (r != SQL_SUCCESS && r != SQL_SUCCESS_WITH_INFO) {
+        qSqlWarning(QStringLiteral("qMakeField: Unable to get autovalue attribute for column ")
+                    + QString::number(column), hStmt);
+        return false;
+    }
+    return nNumericAttribute != SQL_FALSE;
+}
+
 static QSqlField qMakeFieldInfo(const SQLHANDLE hStmt, int i, QString *errorMessage);
 
 // creates a QSqlField from a valid hStmt generated
@@ -662,6 +675,7 @@ static QSqlField qMakeFieldInfo(const SQLHANDLE hStmt, int i, QString *errorMess
     else if (nullable == SQL_NULLABLE)
         f.setRequired(false);
     // else we don't know
+    f.setAutoValue(isAutoValue(hStmt, i));
     return f;
 }
 

src/sql/kernel/qsqlfield.cpp

@@ -531,6 +531,12 @@ QDebug operator<<(QDebug dbg, const QSqlField &f)
     Returns \c true if the value is auto-generated by the database,
     for example auto-increment primary key values.
 
+    \note When using the ODBC driver, due to limitations in the ODBC API,
+    the \c isAutoValue() field is only populated in a QSqlField resulting from a
+    QSqlRecord obtained by executing a \c SELECT query. It is \c false in a QSqlField
+    resulting from a QSqlRecord returned from QSqlDatabase::record() or
+    QSqlDatabase::primaryIndex().
+
     \sa setAutoValue()
 */
 bool QSqlField::isAutoValue() const