#include <mongocxx/v_noabi/mongocxx/read_concern.hpp>

Description

A class to represent the read concern. Read concern can be set at the client, database, or collection level. The read concern can also be provided via connection string, and will be parsed and set on the client constructed for the URI.

For the WiredTiger storage engine, MongoDB 3.2 introduced the readConcern option for replica sets and replica set shards. The readConcern option allows clients to choose a level of isolation for their reads. You can specify a readConcern of "majority" to read data that has been written to a majority of nodes and thus cannot be rolled back. By default, MongoDB uses a readConcern of "local" which does not guarantee that the read data would not be rolled back.

MongoDB 3.4 introduces a read concern level of "linearizable" to read data that has been written to a majority of nodes (i.e. cannot be rolled back) and is not stale. Linearizable read concern is available for all MongoDB supported storage engines and applies to read operations on a single document. Note that writes must be made with majority write concern in order for reads to be linearizable.

See also

Read Concern (MongoDB Manual)

Public Types
enum class	level
	A class to represent the read concern level for read operations. More...

Public Member Functions
	read_concern ()
	Constructs a new read_concern with default acknowledge_level of k_server_default.

	read_concern (const read_concern &)
	Copy constructs a read_concern.

	read_concern (read_concern &&) noexcept
	Move constructs a read_concern.

	~read_concern ()
	Destroys a read_concern.

level	acknowledge_level () const
	Gets the current read concern level.

void	acknowledge_level (level rc_level)
	Sets the read concern level.

bsoncxx::v_noabi::stdx::string_view	acknowledge_string () const
	Gets the current read concern string.

void	acknowledge_string (bsoncxx::v_noabi::stdx::string_view rc_string)
	Sets the read concern string. Any valid read concern string (e.g. "local", "majority", "linearizable", "") may be passed in. For forward-compatibility with read concern levels introduced in the future, no validation is performed on this string.

read_concern &	operator= (const read_concern &)
	Copy assigns a read_concern.

read_concern &	operator= (read_concern &&) noexcept
	Move assigns a read_concern.

bsoncxx::v_noabi::document::value	to_document () const
	Gets the document form of this read_concern.

Related Symbols
(Note that these are not member symbols.)

bool	operator== (const read_concern &, const read_concern &)
	Compares two read_concern objects for (in)-equality.

bool	operator!= (const read_concern &, const read_concern &)
	Compares two read_concern objects for (in)-equality.

Member Enumeration Documentation

◆ level

enum class mongocxx::v_noabi::read_concern::level

strong

A class to represent the read concern level for read operations.

See also

Enumerator
k_local	Represent read concern level "local".
k_majority	Represent read concern level "majority".
k_linearizable	Represent read concern level "linearizable".
k_server_default	Represent the server's default read concern level.
k_unknown	Represent an unknown read concern level.
k_available	Represent read concern level "available".
k_snapshot	Represent read concern level "snapshot".

Constructor & Destructor Documentation

◆ read_concern() [1/3]

mongocxx::v_noabi::read_concern::read_concern ( )

Constructs a new read_concern with default acknowledge_level of k_server_default.

The k_server_default acknowledge level has an empty acknowledge_string. Queries that run with this read_concern will use the server's default read_concern instead of specifying one.

◆ read_concern() [2/3]

mongocxx::v_noabi::read_concern::read_concern ( const read_concern & )

Copy constructs a read_concern.

◆ read_concern() [3/3]

mongocxx::v_noabi::read_concern::read_concern ( read_concern && )

noexcept

Move constructs a read_concern.

◆ ~read_concern()

mongocxx::v_noabi::read_concern::~read_concern ( )

Destroys a read_concern.

Member Function Documentation

◆ acknowledge_level() [1/2]

level mongocxx::v_noabi::read_concern::acknowledge_level ( ) const

Gets the current read concern level.

If this was set with acknowledge_string to anything other than "local", "majority", "linearizable", or an empty string, this will return k_unknown.

Returns: The read concern level.

◆ acknowledge_level() [2/2]

void mongocxx::v_noabi::read_concern::acknowledge_level ( level rc_level )

Sets the read concern level.

Parameters

rc_level Either k_local, k_majority, k_linearizable, or k_server_default.

Exceptions

mongocxx::v_noabi::exception if rc_level is not k_local, k_majority, k_linearizable, or k_server_default.

◆ acknowledge_string() [1/2]

bsoncxx::v_noabi::stdx::string_view mongocxx::v_noabi::read_concern::acknowledge_string ( ) const

Gets the current read concern string.

If the read concern level was set with acknowledge_level, this will return either "local", "majority", "linearizable", or an empty string for k_server_default.

Returns: The read concern string.

◆ acknowledge_string() [2/2]

void mongocxx::v_noabi::read_concern::acknowledge_string ( bsoncxx::v_noabi::stdx::string_view rc_string )

Sets the read concern string. Any valid read concern string (e.g. "local", "majority", "linearizable", "") may be passed in. For forward-compatibility with read concern levels introduced in the future, no validation is performed on this string.

Parameters

rc_string The read concern string.

◆ operator=() [1/2]

read_concern & mongocxx::v_noabi::read_concern::operator= ( const read_concern & )

Copy assigns a read_concern.

◆ operator=() [2/2]

read_concern & mongocxx::v_noabi::read_concern::operator= ( read_concern && )

noexcept

Move assigns a read_concern.

◆ to_document()

bsoncxx::v_noabi::document::value mongocxx::v_noabi::read_concern::to_document ( ) const

Gets the document form of this read_concern.

Returns: Document representation of this read_concern.

Friends And Related Symbol Documentation

◆ operator!=

bool operator!=	(	const read_concern &	,
		const read_concern &	)

friend

Compares two read_concern objects for (in)-equality.

◆ operator==

bool operator==	(	const read_concern &	,
		const read_concern &	)