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#pragma once
#include <Storages/StorageInMemoryMetadata.h>
namespace DB
{
class IStorage;
/// Snapshot of storage that fixes set columns that can be read in query.
/// There are 3 sources of columns: regular columns from metadata,
/// dynamic columns from object Types, virtual columns.
struct StorageSnapshot
{
const IStorage & storage;
const StorageMetadataPtr metadata;
const ColumnsDescription object_columns;
/// Additional data, on which set of columns may depend.
/// E.g. data parts in MergeTree, list of blocks in Memory, etc.
struct Data
{
virtual ~Data() = default;
};
using DataPtr = std::unique_ptr<Data>;
DataPtr data;
/// Projection that is used in query.
mutable const ProjectionDescription * projection = nullptr;
StorageSnapshot(
const IStorage & storage_,
StorageMetadataPtr metadata_)
: storage(storage_), metadata(std::move(metadata_))
{
init();
}
StorageSnapshot(
const IStorage & storage_,
StorageMetadataPtr metadata_,
ColumnsDescription object_columns_)
: storage(storage_)
, metadata(std::move(metadata_))
, object_columns(std::move(object_columns_))
{
init();
}
StorageSnapshot(
const IStorage & storage_,
StorageMetadataPtr metadata_,
ColumnsDescription object_columns_,
DataPtr data_)
: storage(storage_)
, metadata(std::move(metadata_))
, object_columns(std::move(object_columns_))
, data(std::move(data_))
{
init();
}
/// Get all available columns with types according to options.
NamesAndTypesList getColumns(const GetColumnsOptions & options) const;
/// Get columns with types according to options only for requested names.
NamesAndTypesList getColumnsByNames(const GetColumnsOptions & options, const Names & names) const;
/// Get column with type according to options for requested name.
std::optional<NameAndTypePair> tryGetColumn(const GetColumnsOptions & options, const String & column_name) const;
NameAndTypePair getColumn(const GetColumnsOptions & options, const String & column_name) const;
/// Block with ordinary + materialized + aliases + virtuals + subcolumns.
Block getSampleBlockForColumns(const Names & column_names) const;
ColumnsDescription getDescriptionForColumns(const Names & column_names) const;
/// Verify that all the requested names are in the table and are set correctly:
/// list of names is not empty and the names do not repeat.
void check(const Names & column_names) const;
DataTypePtr getConcreteType(const String & column_name) const;
void addProjection(const ProjectionDescription * projection_) const { projection = projection_; }
/// If we have a projection then we should use its metadata.
StorageMetadataPtr getMetadataForQuery() const { return projection ? projection->metadata : metadata; }
private:
void init();
std::unordered_map<String, DataTypePtr> virtual_columns;
/// System columns are not visible in the schema but might be persisted in the data.
/// One example of such column is lightweight delete mask '_row_exists'.
std::unordered_map<String, DataTypePtr> system_columns;
};
using StorageSnapshotPtr = std::shared_ptr<StorageSnapshot>;
}
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