mirror of
https://github.com/matrix-construct/construct
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92 lines
2.9 KiB
C++
92 lines
2.9 KiB
C++
// Matrix Construct
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//
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// Copyright (C) Matrix Construct Developers, Authors & Contributors
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// Copyright (C) 2016-2018 Jason Volk <jason@zemos.net>
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//
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// Permission to use, copy, modify, and/or distribute this software for any
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// purpose with or without fee is hereby granted, provided that the above
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// copyright notice and this permission notice is present in all copies. The
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// full license for this software is available in the LICENSE file.
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#pragma once
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#define HAVE_IRCD_DB_INDEX_H
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namespace ircd::db
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{
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struct index;
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}
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/// An index is a glorified column; the database descriptor for this column
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/// must specify a prefix-extractor otherwise this index just behaves like
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/// a regular key/value column. Index is used to create iterable domains of
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/// a column which all share the same key-prefix.
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///
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/// The index allows a concatenation of two strings to form a key. This con-
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/// catenated key is still unique for the column as a whole and is stored as
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/// the full concatenation -- however, as stated above the prefix function must
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/// be aware of how such a concatenation can be separated back into two
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/// strings.
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///
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/// db::index allows the user to query for either just the first string, or
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/// the whole concatenation. In either case, the resulting iterator can move
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/// only around the keys and values within the domain of that first string.
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/// The iterator presents the user with it.first = second string only, thereby
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/// hiding the prefix allowing for easier iteration of the domain.
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///
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/// Index is not good at reverse iteration due to limitations in RocksDB. Thus
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/// it's better to just flip the comparator function for the column.
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///
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struct ircd::db::index
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:column
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{
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struct const_iterator_base;
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struct const_iterator;
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struct const_reverse_iterator;
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using iterator_type = const_iterator;
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using const_iterator_type = const_iterator;
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static const gopts applied_opts;
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const_iterator end(const string_view &key, gopts = {});
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const_iterator begin(const string_view &key, gopts = {});
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const_reverse_iterator rend(const string_view &key, gopts = {});
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const_reverse_iterator rbegin(const string_view &key, gopts = {});
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using column::column;
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};
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struct ircd::db::index::const_iterator_base
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:ircd::db::column::const_iterator_base
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{
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friend class index;
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const value_type &operator*() const;
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const value_type *operator->() const;
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using column::const_iterator_base::const_iterator_base;
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template<class pos> friend bool seek(index::const_iterator_base &, const pos &, gopts = {});
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};
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struct ircd::db::index::const_iterator
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:ircd::db::index::const_iterator_base
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{
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friend class index;
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const_iterator &operator++();
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const_iterator &operator--();
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using index::const_iterator_base::const_iterator_base;
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};
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struct ircd::db::index::const_reverse_iterator
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:ircd::db::index::const_iterator_base
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{
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friend class index;
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const_reverse_iterator &operator++();
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const_reverse_iterator &operator--();
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using index::const_iterator_base::const_iterator_base;
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};
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