BREAKING: Change RowSet constructor to read already fetched Statement row

Author: asfernandes

src/fb-cpp/Attachment.cpp

@@ -147,7 +147,8 @@ RowSet Attachment::queryPreparedRowSet(Statement& statement, Transaction& transa
 			throw FbCppException("Cannot use non-query SQL with Attachment::queryRowSet");
 	}
 
-	const auto hasRow = statement.execute(transaction);
+	statement.execute(transaction);
 	const auto effectiveMaxRows = statement.getType() == StatementType::EXEC_PROCEDURE ? 1u : maxRows;
-	return RowSet{statement, hasRow ? effectiveMaxRows : 0u, hasRow};
+
+	return RowSet{statement, effectiveMaxRows};
 }

src/fb-cpp/RowSet.cpp

@@ -33,18 +33,13 @@ using namespace fbcpp::impl;
 
 
 RowSet::RowSet(Statement& statement, unsigned maxRows)
-	: RowSet{statement, maxRows, false}
-{
-}
-
-RowSet::RowSet(Statement& statement, unsigned maxRows, bool includeCurrentRow)
 	: client{&statement.getAttachment().getClient()},
 	  statusWrapper{statement.getAttachment().getClient()},
 	  numericConverter{statement.getAttachment().getClient()},
 	  calendarConverter{statement.getAttachment().getClient()}
 {
 	assert(statement.isValid());
-	assert(includeCurrentRow || statement.getResultSetHandle());
+	assert(statement.hasCurrentRow() || statement.getResultSetHandle());
 
 	descriptors = statement.getOutputDescriptors();
 
@@ -56,13 +51,14 @@ RowSet::RowSet(Statement& statement, unsigned maxRows, bool includeCurrentRow)
 	auto resultSet = statement.getResultSetHandle();
 	auto* dest = buffer.data();
 
-	if (includeCurrentRow && maxRows > 0u)
+	if (statement.hasCurrentRow() && maxRows > 0u)
 	{
 		auto& currentRow = statement.getOutputMessage();
 		assert(currentRow.size() == messageLength);
 		std::copy(currentRow.begin(), currentRow.end(), dest);
 		dest += messageLength;
 		++count;
+		statement.clearCurrentRow();
 	}
 
 	if (!resultSet)

src/fb-cpp/RowSet.h

@@ -58,26 +58,18 @@ namespace fbcpp
 
 	public:
 		///
-		/// @brief Fetches up to `maxRows` rows from the current result set of
-		/// `statement`.
+		/// @brief Fetches up to `maxRows` rows from `statement`.
 		///
-		/// The statement must have an open result set (i.e. `execute()` was
-		/// called and it is a SELECT-type statement). Rows are fetched via
-		/// `IResultSet::fetchNext()` directly into the internal buffer.
+		/// If `statement` is positioned on a current row (typically the row already
+		/// fetched by `execute()` or a later fetch), that row is copied first and then
+		/// consumed so a subsequent `RowSet` does not duplicate it. Remaining rows are
+		/// fetched via `IResultSet::fetchNext()` directly into the internal buffer.
 		///
-		/// @param statement The statement with an open result set.
+		/// @param statement The statement with a current row and/or an open result set.
 		/// @param maxRows Maximum number of rows to fetch.
 		///
 		explicit RowSet(Statement& statement, unsigned maxRows);
 
-		///
-		/// @brief Fetches up to `maxRows` rows from the current result set of `statement`.
-		///
-		/// When `includeCurrentRow` is true, the current output message already fetched by `statement.execute()` is
-		/// copied as the first row before fetching the remaining rows from the result set.
-		///
-		explicit RowSet(Statement& statement, unsigned maxRows, bool includeCurrentRow);
-
 		RowSet(RowSet&& o) noexcept
 			: client{o.client},
 			  count{o.count},

src/fb-cpp/Statement.cpp

@@ -196,9 +196,11 @@ Statement::Statement(Statement&& o) noexcept
 	  outMessage{std::move(o.outMessage)},
 	  outRow{std::make_unique<Row>(attachment->getClient(), outDescriptors, std::span{outMessage})},
 	  type{o.type},
-	  cursorFlags{o.cursorFlags}
+	  cursorFlags{o.cursorFlags},
+	  currentRow{o.currentRow}
 {
 	o.outRow.reset();
+	o.currentRow = false;
 }
 
 Statement& Statement::operator=(Statement&& o) noexcept
@@ -220,8 +222,10 @@ Statement& Statement::operator=(Statement&& o) noexcept
 		outRow = std::make_unique<Row>(attachment->getClient(), outDescriptors, std::span{outMessage});
 		type = o.type;
 		cursorFlags = o.cursorFlags;
+		currentRow = o.currentRow;
 
 		o.outRow.reset();
+		o.currentRow = false;
 	}
 
 	return *this;
@@ -237,6 +241,7 @@ void Statement::free()
 		resultSetHandle.reset();
 	}
 
+	currentRow = false;
 	statementHandle->free(&statusWrapper);
 	statementHandle.reset();
 }
@@ -266,6 +271,8 @@ bool Statement::execute(Transaction& transaction)
 		resultSetHandle.reset();
 	}
 
+	currentRow = false;
+
 	const auto outMessageData = outMessage.data();
 
 	if (outMessageData)
@@ -280,11 +287,13 @@ bool Statement::execute(Transaction& transaction)
 		case StatementType::SELECT_FOR_UPDATE:
 			resultSetHandle.reset(statementHandle->openCursor(&statusWrapper, transaction.getHandle().get(),
 				inMetadata.get(), inMessage.data(), outMetadata.get(), cursorFlags));
-			return resultSetHandle->fetchNext(&statusWrapper, outMessageData) == fb::IStatus::RESULT_OK;
+			currentRow = resultSetHandle->fetchNext(&statusWrapper, outMessageData) == fb::IStatus::RESULT_OK;
+			return currentRow;
 
 		default:
 			statementHandle->execute(&statusWrapper, transaction.getHandle().get(), inMetadata.get(), inMessage.data(),
 				outMetadata.get(), outMessageData);
+			currentRow = !outDescriptors.empty();
 			return true;
 	}
 }
@@ -298,43 +307,52 @@ bool Statement::fetchNext()
 {
 	assert(isValid());
 
-	return resultSetHandle && resultSetHandle->fetchNext(&statusWrapper, outMessage.data()) == fb::IStatus::RESULT_OK;
+	currentRow = resultSetHandle && resultSetHandle->fetchNext(&statusWrapper, outMessage.data()) == fb::IStatus::RESULT_OK;
+	return currentRow;
 }
 
 bool Statement::fetchPrior()
 {
 	assert(isValid());
 
-	return resultSetHandle && resultSetHandle->fetchPrior(&statusWrapper, outMessage.data()) == fb::IStatus::RESULT_OK;
+	currentRow =
+		resultSetHandle && resultSetHandle->fetchPrior(&statusWrapper, outMessage.data()) == fb::IStatus::RESULT_OK;
+	return currentRow;
 }
 
 bool Statement::fetchFirst()
 {
 	assert(isValid());
 
-	return resultSetHandle && resultSetHandle->fetchFirst(&statusWrapper, outMessage.data()) == fb::IStatus::RESULT_OK;
+	currentRow =
+		resultSetHandle && resultSetHandle->fetchFirst(&statusWrapper, outMessage.data()) == fb::IStatus::RESULT_OK;
+	return currentRow;
 }
 
 bool Statement::fetchLast()
 {
 	assert(isValid());
 
-	return resultSetHandle && resultSetHandle->fetchLast(&statusWrapper, outMessage.data()) == fb::IStatus::RESULT_OK;
+	currentRow =
+		resultSetHandle && resultSetHandle->fetchLast(&statusWrapper, outMessage.data()) == fb::IStatus::RESULT_OK;
+	return currentRow;
 }
 
 bool Statement::fetchAbsolute(unsigned position)
 {
 	assert(isValid());
 
-	return resultSetHandle &&
+	currentRow = resultSetHandle &&
 		resultSetHandle->fetchAbsolute(&statusWrapper, static_cast<int>(position), outMessage.data()) ==
-		fb::IStatus::RESULT_OK;
+			fb::IStatus::RESULT_OK;
+	return currentRow;
 }
 
 bool Statement::fetchRelative(int offset)
 {
 	assert(isValid());
 
-	return resultSetHandle &&
+	currentRow = resultSetHandle &&
 		resultSetHandle->fetchRelative(&statusWrapper, offset, outMessage.data()) == fb::IStatus::RESULT_OK;
+	return currentRow;
 }

src/fb-cpp/Statement.h

@@ -141,6 +141,8 @@ namespace fbcpp
 	///
 	class FB_CPP_EXPORT Statement final
 	{
+		friend class RowSet;
+
 	public:
 		///
 		/// Prepares an SQL statement.
@@ -209,6 +211,17 @@ namespace fbcpp
 			return statementHandle != nullptr;
 		}
 
+		///
+		/// Returns whether the statement is positioned on a current output row.
+		///
+		/// A current row is present after a successful `execute()` or fetch that produced
+		/// output, until the row is consumed by `RowSet` or replaced by a later fetch.
+		///
+		bool hasCurrentRow() const noexcept
+		{
+			return currentRow;
+		}
+
 		///
 		/// @brief Provides direct access to the underlying Firebird statement handle.
 		/// @return Smart pointer to the low-level `fb::IStatement` interface.
@@ -2260,6 +2273,11 @@ namespace fbcpp
 	private:
 		Client& getClient() noexcept;
 
+		void clearCurrentRow() noexcept
+		{
+			currentRow = false;
+		}
+
 	private:
 		Attachment* attachment;
 		impl::StatusWrapper statusWrapper;
@@ -2276,6 +2294,7 @@ namespace fbcpp
 		std::unique_ptr<Row> outRow;
 		StatementType type;
 		unsigned cursorFlags = 0;
+		bool currentRow = false;
 	};
 
 	///