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

#pragma once

#include <DB/Dictionaries/IDictionarySource.h>
#include <DB/Dictionaries/MongoDBBlockInputStream.h>
#include <Poco/Util/AbstractConfiguration.h>
#include <mongo/client/dbclient.h>
#include <ext/collection_cast.hpp>
#include <ext/enumerate.hpp>
#include <ext/size.hpp>


namespace DB
{

namespace ErrorCodes
{
	extern const int UNSUPPORTED_METHOD;
	extern const int WRONG_PASSWORD;
	extern const int MONGODB_INIT_FAILED;
}


/// Allows loading dictionaries from a MongoDB collection
class MongoDBDictionarySource final : public IDictionarySource
{
	static const auto max_block_size = 8192;

	MongoDBDictionarySource(
		const DictionaryStructure & dict_struct, const std::string & host, const std::string & port,
		const std::string & user, const std::string & password,
		const std::string & db, const std::string & collection,
		const Block & sample_block, Context & context)
		: dict_struct{dict_struct}, host{host}, port{port}, user{user}, password{password},
		  db{db}, collection{collection}, sample_block{sample_block}, context(context),
		  connection{true}
	{
		init();

		connection.connect(host + ':' + port);

		/// @todo: should connection.auth be called after or before .connect ?
		if (!user.empty())
		{
			std::string error;
			if (!connection.auth(db, user, password, error))
				throw DB::Exception{
					"Could not authenticate to a MongoDB database " + db + " with provided credentials: " + error,
					ErrorCodes::WRONG_PASSWORD
				};
		}

		/// compose BSONObj containing all requested fields
		mongo::BSONObjBuilder builder;
		builder << "_id" << 0;

		for (const auto & column : sample_block.getColumns())
			builder << column.name << 1;

		fields_to_query = builder.obj();
	}

	/// mongo-cxx driver requires global initialization before using any functionality
	static void init()
	{
		static const auto mongo_init_status = mongo::client::initialize();

		if (!mongo_init_status.isOK())
			throw DB::Exception{
				"mongo::client::initialize() failed: " + mongo_init_status.toString(),
				ErrorCodes::MONGODB_INIT_FAILED
			};

		LOG_TRACE(&Logger::get("MongoDBDictionarySource"), "mongo::client::initialize() ok");
	}

public:
	MongoDBDictionarySource(
		const DictionaryStructure & dict_struct, const Poco::Util::AbstractConfiguration & config,
		const std::string & config_prefix, Block & sample_block, Context & context)
		: MongoDBDictionarySource{
			dict_struct,
			config.getString(config_prefix + ".host"),
			config.getString(config_prefix + ".port"),
			config.getString(config_prefix + ".user", ""),
			config.getString(config_prefix + ".password", ""),
			config.getString(config_prefix + ".db", ""),
			config.getString(config_prefix + ".collection"),
			sample_block, context
		}
	{
	}

	MongoDBDictionarySource(const MongoDBDictionarySource & other)
		: MongoDBDictionarySource{
			other.dict_struct, other.host, other.port, other.user, other.password,
			other.db, other.collection, other.sample_block, other.context
		}
	{
	}

	BlockInputStreamPtr loadAll() override
	{
		return new MongoDBBlockInputStream{
			connection.query(db + '.' + collection, {}, 0, 0, &fields_to_query),
			sample_block, max_block_size
		};
	}

	bool supportsSelectiveLoad() const override { return true; }

	BlockInputStreamPtr loadIds(const std::vector<std::uint64_t> & ids) override
	{
		if (!dict_struct.id)
			throw Exception{"'id' is required for selective loading", ErrorCodes::UNSUPPORTED_METHOD};

		/// mongo::BSONObj has shitty design and does not use fixed width integral types
		const auto query = BSON(
			dict_struct.id->name << BSON("$in" << ext::collection_cast<std::vector<long long int>>(ids)));

		return new MongoDBBlockInputStream{
			connection.query(db + '.' + collection, query, 0, 0, &fields_to_query),
			sample_block, max_block_size
		};
	}

	BlockInputStreamPtr loadKeys(
		const ConstColumnPlainPtrs & key_columns, const std::vector<std::size_t> & requested_rows) override
	{
		if (!dict_struct.key)
			throw Exception{"'key' is required for selective loading", ErrorCodes::UNSUPPORTED_METHOD};

		std::string query_string;

		{
			WriteBufferFromString out{query_string};

			writeString("{$or:[", out);

			auto first = true;

			for (const auto row : requested_rows)
			{
				if (!first)
					writeChar(',', out);

				first = false;

				writeChar('{', out);

				for (const auto idx_key : ext::enumerate(*dict_struct.key))
				{
					if (idx_key.first != 0)
						writeChar(',', out);

					writeString(idx_key.second.name, out);
					writeChar(':', out);
					idx_key.second.type->serializeTextQuoted(*key_columns[idx_key.first], row, out);
				}

				writeChar('}', out);
			}

			writeString("]}", out);
		}

		return new MongoDBBlockInputStream{
			connection.query(db + '.' + collection, query_string, 0, 0, &fields_to_query),
			sample_block, max_block_size
		};
	}

	/// @todo: for MongoDB, modification date can somehow be determined from the `_id` object field
	bool isModified() const override { return false; }

	DictionarySourcePtr clone() const override { return std::make_unique<MongoDBDictionarySource>(*this); }

	std::string toString() const override
	{
		return "MongoDB: " + db + '.' + collection + ',' + (user.empty() ? " " : " " + user + '@') + host + ':' + port;
	}

private:
	const DictionaryStructure dict_struct;
	const std::string host;
	const std::string port;
	const std::string user;
	const std::string password;
	const std::string db;
	const std::string collection;
	Block sample_block;
	Context & context;

	mongo::DBClientConnection connection;
	mongo::BSONObj fields_to_query;
};

}