ClickHouse/dbms/src/Storages/System/IStorageSystemOneBlock.h

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#pragma once
#include <DataStreams/OneBlockInputStream.h>
#include <DataTypes/DataTypeString.h>
#include <Storages/ColumnsDescription.h>
#include <Storages/IStorage.h>
#include <ext/shared_ptr_helper.h>
namespace DB
{
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class Context;
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/** Base class for system tables whose all columns have String type.
*/
template <typename Self>
class IStorageSystemOneBlock : public IStorage
{
protected:
virtual void fillData(MutableColumns & res_columns, const Context & context, const SelectQueryInfo & query_info) const = 0;
public:
IStorageSystemOneBlock(const String & name_) : name(name_)
{
setColumns(ColumnsDescription(Self::getNamesAndTypes()));
}
std::string getTableName() const override { return name; }
std::string getDatabaseName() const override { return "system"; }
BlockInputStreams read(const Names & column_names,
const SelectQueryInfo & query_info,
const Context & context,
QueryProcessingStage::Enum /*processed_stage*/,
size_t /*max_block_size*/,
unsigned /*num_streams*/) override
{
check(column_names);
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Block sample_block = getSampleBlock();
MutableColumns res_columns = sample_block.cloneEmptyColumns();
fillData(res_columns, context, query_info);
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return BlockInputStreams(1, std::make_shared<OneBlockInputStream>(sample_block.cloneWithColumns(std::move(res_columns))));
}
private:
const String name;
};
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}