ClickHouse/dbms/include/DB/Storages/StorageNull.h

#pragma once

#include <ext/shared_ptr_helper.hpp>

#include <DB/Core/NamesAndTypes.h>
#include <DB/Storages/IStorage.h>
#include <DB/DataStreams/NullBlockInputStream.h>
#include <DB/DataStreams/NullBlockOutputStream.h>


namespace DB
{

/** При записи, ничего не делает.
  * При чтении, возвращает пустоту.
  */
class StorageNull : private ext::shared_ptr_helper<StorageNull>, public IStorage
{
friend class ext::shared_ptr_helper<StorageNull>;

public:
	static StoragePtr create(
		const std::string & name_,
		NamesAndTypesListPtr columns_,
		const NamesAndTypesList & materialized_columns_,
		const NamesAndTypesList & alias_columns_,
		const ColumnDefaults & column_defaults_)
	{
		return make_shared(name_, columns_, materialized_columns_, alias_columns_, column_defaults_);
	}

	std::string getName() const override { return "Null"; }
	std::string getTableName() const override { return name; }

	const NamesAndTypesList & getColumnsListImpl() const override { return *columns; }

	BlockInputStreams read(
		const Names & column_names,
		ASTPtr query,
		const Context & context,
		const Settings & settings,
		QueryProcessingStage::Enum & processed_stage,
		const size_t max_block_size = DEFAULT_BLOCK_SIZE,
		const unsigned threads = 1) override
	{
		return { std::make_shared<NullBlockInputStream>() };
	}

	BlockOutputStreamPtr write(ASTPtr query, const Settings & settings) override
	{
		return std::make_shared<NullBlockOutputStream>();
	}

	void rename(const String & new_path_to_db, const String & new_database_name, const String & new_table_name) override
	{
		name = new_table_name;
	}

private:
	String name;
	NamesAndTypesListPtr columns;

	StorageNull(
		const std::string & name_,
		NamesAndTypesListPtr columns_,
		const NamesAndTypesList & materialized_columns_,
		const NamesAndTypesList & alias_columns_,
		const ColumnDefaults & column_defaults_)
		: IStorage{materialized_columns_, alias_columns_, column_defaults_}, name(name_), columns(columns_) {}
};

}