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#pragma once
///
/// @file yt/cpp/mapreduce/interface/skiff_row.h
/// Header containing interfaces that you need to define for using TSkiffRowTableReader
/// What you need to do for your struct type TMyType:
/// 1. Write `true` specialization TIsSkiffRow<TMyType>;
/// 2. Write specialization GetSkiffSchema<TMyType>();
/// 3. Write your own parser derived from ISkiffRowParser and write specialization GetSkiffParser<TMyType>() which returns this parser.
#include "fwd.h"
#include <yt/cpp/mapreduce/skiff/skiff_schema.h>
#include <yt/cpp/mapreduce/interface/format.h>
#include <library/cpp/skiff/skiff.h>
#include <util/generic/maybe.h>
namespace NYT {
////////////////////////////////////////////////////////////////////////////////
//! Need to write `true_type` specialization for your row type `T`.
/// And implement two functions: `GetSkiffSchema` and `CreateSkiffParser`.
///
/// Example:
///
/// template <>
/// struct TIsSkiffRow<T>
/// : std::true_type
/// { };
///
template<class T>
struct TIsSkiffRow
: std::false_type
{ };
////////////////////////////////////////////////////////////////////////////////
//! Return skiff schema for row type `T` which will be requested.
/// Need to write its specialization.
template <typename T>
NSkiff::TSkiffSchemaPtr GetSkiffSchema(const TMaybe<TSkiffRowHints>& /*hints*/)
{
static_assert(TDependentFalse<T>, "Unimplemented `GetSkiffSchema` method");
}
//! Return skiff schema for row type `T` which will be used for skiff parser.
/// By default, it is equal to the requested schema.
template <typename T>
NSkiff::TSkiffSchemaPtr GetParserSkiffSchema(const TMaybe<TSkiffRowHints>& hints)
{
return GetSkiffSchema<T>(hints);
}
////////////////////////////////////////////////////////////////////////////////
//! Allow to parse rows as user's structs from stream (TCheckedInDebugSkiffParser).
/// Need to write derived class for your own row type.
///
/// Example:
///
/// class TMySkiffRowParser : public ISkiffRowParser
/// {
/// public:
/// TMySkiffRowParser(TMySkiffRow* row)
/// : Row_(row)
/// {}
///
/// void Parse(NSkiff::TCheckedInDebugSkiffParser* parser)
/// . {
/// Row_->SomeInt64Field = parser->ParseInt64();
/// }
///
/// private:
/// TMySkiffRow* Row_;
/// }
///
class ISkiffRowParser
: public TThrRefBase
{
public:
//! Read one row from parser
virtual void Parse(NSkiff::TCheckedInDebugSkiffParser* /*parser*/) = 0;
};
//! Creates a parser for row type `T`.
template <typename T>
ISkiffRowParserPtr CreateSkiffParser(T* /*row*/, const TMaybe<TSkiffRowHints>& /*hints*/)
{
static_assert(TDependentFalse<T>, "Unimplemented `CreateSkiffParser` function");
}
////////////////////////////////////////////////////////////////////////////////
//! Allow to skip row content without getting row.
/// By default row will be parsed using your parser derived from ISkiffRowParser.
/// If you want, you can write more optimal skipper, but it isn't required.
class ISkiffRowSkipper
: public TThrRefBase
{
public:
virtual void SkipRow(NSkiff::TCheckedInDebugSkiffParser* /*parser*/) = 0;
};
//! Default ISkiffRowSkipper implementation.
template <typename T>
class TSkiffRowSkipper : public ISkiffRowSkipper {
public:
explicit TSkiffRowSkipper(const TMaybe<TSkiffRowHints>& hints)
: Parser_(CreateSkiffParser<T>(&Row_, hints))
{ }
void SkipRow(NSkiff::TCheckedInDebugSkiffParser* parser) {
Parser_->Parse(parser);
}
private:
T Row_;
ISkiffRowParserPtr Parser_;
};
//! Creates a skipper for row type 'T'.
/// You don't need to write its specialization.
template <typename T>
ISkiffRowSkipperPtr CreateSkiffSkipper(const TMaybe<TSkiffRowHints>& hints)
{
return ::MakeIntrusive<TSkiffRowSkipper<T>>(hints);
}
////////////////////////////////////////////////////////////////////////////////
} // namespace NYT
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