ClickHouse/dbms/include/DB/Dictionaries/IDictionarySource.h

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#pragma once
#include <DB/DataStreams/IBlockInputStream.h>
#include <vector>
namespace DB
{
class IDictionarySource;
using DictionarySourcePtr = std::unique_ptr<IDictionarySource>;
/** Data-provider interface for external dictionaries,
* abstracts out the data source (file, MySQL, ClickHouse, external program, network request et cetera)
* from the presentation and memory layout (the dictionary itself).
*/
class IDictionarySource
{
public:
/// returns an input stream with all the data available from this source
virtual BlockInputStreamPtr loadAll() = 0;
/** Indicates whether this source supports "random access" loading of data
* loadId and loadIds can only be used if this function returns true.
*/
virtual bool supportsSelectiveLoad() const = 0;
/// returns an input stream with the data for a collection of identifiers
virtual BlockInputStreamPtr loadIds(const std::vector<UInt64> & ids) = 0;
/** returns an input stream with the data for a collection of composite keys.
* `requested_rows` contains indices of all rows containing unique keys. */
virtual BlockInputStreamPtr loadKeys(
const ConstColumnPlainPtrs & key_columns, const std::vector<std::size_t> & requested_rows) = 0;
/// indicates whether the source has been modified since last load* operation
virtual bool isModified() const = 0;
virtual DictionarySourcePtr clone() const = 0;
/// returns an informal string describing the source
virtual std::string toString() const = 0;
virtual ~IDictionarySource() = default;
};
}