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#pragma once
#include <Core/NamesAndAliases.h>
#include <DataTypes/DataTypeString.h>
#include <Storages/ColumnsDescription.h>
#include <Storages/IStorage.h>
#include <Storages/SelectQueryInfo.h>
#include <Storages/System/getQueriedColumnsMaskAndHeader.h>
#include <Processors/Sources/SourceFromSingleChunk.h>
#include <QueryPipeline/Pipe.h>
namespace DB
{
class Context;
/** IStorageSystemOneBlock is base class for system tables whose all columns can be synchronously fetched.
*
* Client class need to provide static method static NamesAndTypesList getNamesAndTypes() that will return list of column names and
* their types. IStorageSystemOneBlock during read will create result columns in same order as result of getNamesAndTypes
* and pass it with fillData method.
*
* Client also must override fillData and fill result columns.
*
* If subclass want to support virtual columns, it should override getVirtuals method of IStorage interface.
* IStorageSystemOneBlock will add virtuals columns at the end of result columns of fillData method.
*/
template <typename Self>
class IStorageSystemOneBlock : public IStorage
{
protected:
virtual void fillData(MutableColumns & res_columns, ContextPtr context, const SelectQueryInfo & query_info) const = 0;
virtual bool supportsColumnsMask() const { return false; }
public:
explicit IStorageSystemOneBlock(const StorageID & table_id_) : IStorage(table_id_)
{
StorageInMemoryMetadata storage_metadata;
storage_metadata.setColumns(ColumnsDescription(Self::getNamesAndTypes(), Self::getNamesAndAliases()));
setInMemoryMetadata(storage_metadata);
}
Pipe read(
const Names & column_names,
const StorageSnapshotPtr & storage_snapshot,
SelectQueryInfo & query_info,
ContextPtr context,
QueryProcessingStage::Enum /*processed_stage*/,
size_t /*max_block_size*/,
size_t /*num_streams*/) override
{
storage_snapshot->check(column_names);
Block sample_block = storage_snapshot->metadata->getSampleBlockWithVirtuals(getVirtuals());
if (supportsColumnsMask())
{
auto [columns_mask, header] = getQueriedColumnsMaskAndHeader(sample_block, column_names);
query_info.columns_mask = std::move(columns_mask);
sample_block = std::move(header);
}
MutableColumns res_columns = sample_block.cloneEmptyColumns();
fillData(res_columns, context, query_info);
UInt64 num_rows = res_columns.at(0)->size();
Chunk chunk(std::move(res_columns), num_rows);
return Pipe(std::make_shared<SourceFromSingleChunk>(sample_block, std::move(chunk)));
}
bool isSystemStorage() const override { return true; }
static NamesAndAliases getNamesAndAliases() { return {}; }
};
}
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