A class to represent the read concern. More...

#include <read_concern.hpp>

Public Types
enum class	level
	A class to represent the read concern level. 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 &	operator= (const read_concern &)
	Copy assigns a read_concern.

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

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

	~read_concern ()
	Destroys a read_concern.

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

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

void	acknowledge_string (stdx::string_view rc_string)
	Sets the read concern string.

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

Detailed 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: https://docs.mongodb.com/master/reference/read-concern/

Member Enumeration Documentation

◆ level

enum class mongocxx::read_concern::level

strong

A class to represent the read concern level.

See also: https://docs.mongodb.com/master/reference/read-concern/#read-concern-levels

Constructor & Destructor Documentation

◆ read_concern()

mongocxx::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.

Member Function Documentation

◆ acknowledge_level() [1/2]

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

◆ acknowledge_string() [1/2]

stdx::string_view mongocxx::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::read_concern::acknowledge_string ( 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.