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// Copyright (C) MongoDB, Inc. 2017-present.
// Licensed under the Apache License, Version 2.0 (the "License"); you may
// not use this file except in compliance with the License. You may obtain
// a copy of the License at
package readconcern // import ""
import (
// ReadConcern for replica sets and replica set shards determines which data to return from a query.
type ReadConcern struct {
level string
// Option is an option to provide when creating a ReadConcern.
type Option func(concern *ReadConcern)
// Level creates an option that sets the level of a ReadConcern.
func Level(level string) Option {
return func(concern *ReadConcern) {
concern.level = level
// Local specifies that the query should return the instance’s most recent data.
func Local() *ReadConcern {
return New(Level("local"))
// Majority specifies that the query should return the instance’s most recent data acknowledged as
// having been written to a majority of members in the replica set.
func Majority() *ReadConcern {
return New(Level("majority"))
// Linearizable specifies that the query should return data that reflects all successful writes
// issued with a write concern of "majority" and acknowledged prior to the start of the read operation.
func Linearizable() *ReadConcern {
return New(Level("linearizable"))
// Available specifies that the query should return data from the instance with no guarantee
// that the data has been written to a majority of the replica set members (i.e. may be rolled back).
func Available() *ReadConcern {
return New(Level("available"))
// Snapshot is only available for operations within multi-document transactions.
func Snapshot() *ReadConcern {
return New(Level("snapshot"))
// New constructs a new read concern from the given string.
func New(options ...Option) *ReadConcern {
concern := &ReadConcern{}
for _, option := range options {
return concern
// MarshalBSONValue implements the bson.ValueMarshaler interface.
func (rc *ReadConcern) MarshalBSONValue() (bsontype.Type, []byte, error) {
var elems []byte
if len(rc.level) > 0 {
elems = bsoncore.AppendStringElement(elems, "level", rc.level)
return bsontype.EmbeddedDocument, bsoncore.BuildDocument(nil, elems), nil
// GetLevel returns the read concern level.
func (rc *ReadConcern) GetLevel() string {
return rc.level
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