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construct/include/ircd/db/domain.h

112 lines
3.4 KiB
C++

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