diff -r 8fd6c4d44071 -r 3613617d3076 src/StreamRelationalWriter.h
--- a/src/StreamRelationalWriter.h	Sun Jul 22 10:26:22 2018 +0200
+++ b/src/StreamRelationalWriter.h	Sun Jul 22 17:19:25 2018 +0200
@@ -28,6 +28,10 @@
 	 * count of columns in the current table
 	 */
 	integer_t columnCount;
+	/**
+	 * number of column (0 = first) that will be written; after writing, the number is increased and prepared for next one
+	 */
+	integer_t currentColumn;
 
 	/**
 	 * types of columns in the current table
@@ -36,7 +40,12 @@
 
 	void writeString(const string_t &stringValue, const TypeId typeId) {
 		for (DataTypeWriterBase* writer : writers) if (writer->supports(typeId)) return writer->writeString(output, stringValue);
-		throw RelpipeWriterException(L"Unsupported data type: " + static_cast<integer_t>(typeId));
+		throw RelpipeWriterException(L"Unsupported data type: " + static_cast<integer_t> (typeId));
+	}
+
+	void writeRaw(const void* value, const type_info& typeInfo, const TypeId typeId) {
+		for (DataTypeWriterBase* writer : writers) if (writer->supports(typeId)) return writer->writeRaw(output, value, typeInfo);
+		throw RelpipeWriterException(L"Unsupported data type: " + static_cast<integer_t> (typeId));
 	}
 
 public:
@@ -52,12 +61,13 @@
 
 	string_t toTypeCode(const TypeId typeId) override {
 		for (DataTypeWriterBase* writer : writers) if (writer->supports(typeId)) return writer->getTypeCode();
-		throw RelpipeWriterException(L"Unsupported data type: " + static_cast<integer_t>(typeId));
+		throw RelpipeWriterException(L"Unsupported data type: " + static_cast<integer_t> (typeId));
 	}
-	
+
 	void startRelation(string_t name, std::vector<std::pair<string_t, TypeId> > attributes, boolean_t writeHeader) override {
 		string_t tableName = name;
 		columnCount = attributes.size();
+		currentColumn = 0;
 
 		// Write table name and column count:
 		integerWriter.writeValue(output, DATA_PART_START);
@@ -76,7 +86,7 @@
 		// Write column types:
 		for (size_t c = 0; c < columnCount; c++) {
 			TypeId typeId = attributes[c].second;
-			integerWriter.writeValue(output, static_cast<integer_t>(typeId));
+			integerWriter.writeValue(output, static_cast<integer_t> (typeId));
 			columnTypes[c] = typeId;
 		}
 
@@ -84,8 +94,9 @@
 
 	void writeRecord(std::vector<string_t> attributes) override {
 		// FIXME: check vector size
+		// FIXME: check currentColumn == 0
 		for (size_t c = 0; c < columnCount; c++) {
-			// TODO: support multiple rows in a single method call?
+			// TODO: do not support multiple rows in a single method call
 			if (c % columnCount == 0) {
 				integerWriter.writeValue(output, DATA_PART_ROW);
 			}
@@ -96,6 +107,12 @@
 		}
 	}
 
+	void writeAttribute(const void* value, const std::type_info& type) override {
+		if (currentColumn == 0) integerWriter.writeValue(output, DATA_PART_ROW);
+		writeRaw(value, type, columnTypes[currentColumn]);
+		if (++currentColumn == columnCount) currentColumn = 0;
+	}
+
 };
 
 }