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#pragma once
#include <Storages/IStorage_fwd.h>
#include <Databases/IDatabase.h>
namespace DB
{
/**
* Implements the IDatabase interface and combines multiple other databases
* Searches for tables in each database in order until found, and delegates operations to the appropriate database
* Useful for combining databases
*
* Used in clickhouse-local to combine DatabaseFileSystem and DatabaseMemory
*/
class DatabasesOverlay : public IDatabase, protected WithContext
{
public:
DatabasesOverlay(const String & name_, ContextPtr context_);
/// Not thread-safe. Use only as factory to initialize database
DatabasesOverlay & registerNextDatabase(DatabasePtr database);
String getEngineName() const override { return "Overlay"; }
public:
bool isTableExist(const String & table_name, ContextPtr context) const override;
StoragePtr tryGetTable(const String & table_name, ContextPtr context) const override;
void createTable(ContextPtr context, const String & table_name, const StoragePtr & table, const ASTPtr & query) override;
void dropTable(ContextPtr context, const String & table_name, bool sync) override;
void attachTable(ContextPtr context, const String & table_name, const StoragePtr & table, const String & relative_table_path) override;
StoragePtr detachTable(ContextPtr context, const String & table_name) override;
ASTPtr getCreateTableQueryImpl(const String & name, ContextPtr context, bool throw_on_error) const override;
ASTPtr getCreateDatabaseQuery() const override;
String getTableDataPath(const String & table_name) const override;
String getTableDataPath(const ASTCreateQuery & query) const override;
UUID tryGetTableUUID(const String & table_name) const override;
void drop(ContextPtr context) override;
void alterTable(ContextPtr local_context, const StorageID & table_id, const StorageInMemoryMetadata & metadata) override;
std::vector<std::pair<ASTPtr, StoragePtr>> getTablesForBackup(const FilterByNameFunction & filter, const ContextPtr & local_context) const override;
void createTableRestoredFromBackup(const ASTPtr & create_table_query, ContextMutablePtr local_context, std::shared_ptr<IRestoreCoordination> restore_coordination, UInt64 timeout_ms) override;
DatabaseTablesIteratorPtr getTablesIterator(ContextPtr context, const FilterByNameFunction & filter_by_table_name) const override;
bool empty() const override;
void shutdown() override;
protected:
std::vector<DatabasePtr> databases;
Poco::Logger * log;
};
}
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