C++ 示例：使用会话参数

#include <string>
#include <sstream>
#include <iostream>
#include "Vertica.h"
#include "VerticaUDx.h"

using namespace Vertica;

class RowCount : public Vertica::ScalarFunction
{
private:
    int rowCount;
    int count;

public:

    virtual void setup(Vertica::ServerInterface &srvInterface, const Vertica::SizedColumnTypes &argTypes) {
        ParamReader pSessionParams = srvInterface.getUDSessionParamReader("library");
        std::string rCount = pSessionParams.containsParameter("rowCount")?
            pSessionParams.getStringRef("rowCount").str(): "0";
        rowCount=atoi(rCount.c_str());

    }
    virtual void processBlock(Vertica::ServerInterface &srvInterface, Vertica::BlockReader &arg_reader, Vertica::BlockWriter &res_writer) {

        count = 0;
        if(arg_reader.getNumCols() != 2)
            vt_report_error(0, "Function only accepts two arguments, but %zu provided", arg_reader.getNumCols());

        do {
            const Vertica::vint a = arg_reader.getIntRef(0);
            const Vertica::vint b = arg_reader.getIntRef(1);
            res_writer.setInt(a+b);
            count++;
            res_writer.next();
        } while (arg_reader.next());

        srvInterface.log("count %d", count);

        }

        virtual void destroy(ServerInterface &srvInterface, const SizedColumnTypes &argTypes, SessionParamWriterMap &udParams) {
            rowCount = rowCount + count;

            std:ostringstream s;
            s << rowCount;
            const std::string i_as_string(s.str());

            udParams.getUDSessionParamWriter("library").getStringRef("rowCount").copy(i_as_string);

        }
};

class RowCountsInfo : public Vertica::ScalarFunctionFactory {
    virtual Vertica::ScalarFunction *createScalarFunction(Vertica::ServerInterface &srvInterface)
    { return Vertica::vt_createFuncObject<RowCount>(srvInterface.allocator);
    }

    virtual void getPrototype(Vertica::ServerInterface &srvInterface, Vertica::ColumnTypes &argTypes, Vertica::ColumnTypes &returnType)
    {
        argTypes.addInt();
        argTypes.addInt();
        returnType.addInt();
    }
};

RegisterFactory(RowCountsInfo);