storages::mongo::options::Projection Class Reference

#include <userver/storages/mongo/options.hpp>

Detailed Description

Selects fields to be returned.

Note

_id field is always included by default, order might be significant

See also

https://docs.mongodb.com/manual/tutorial/project-fields-from-query-results/

Definition at line 158 of file options.hpp.

Public Member Functions
	Projection ()=default
	Creates a default projection including all fields.
	Projection (std::initializer_list< std::string_view > fields_to_include)
	Creates a projection including only specified fields.
Projection &	Include (std::string_view field)
	Includes a field into the projection.
Projection &	Exclude (std::string_view field)
	Excludes a field from the projection.
Projection &	Slice (std::string_view field, int32_t limit, int32_t skip=0)
	Setups an array slice in the projection.
Projection &	ElemMatch (std::string_view field, const formats::bson::Document &pred)
	Matches the first element of an array satisfying a predicate.

Member Function Documentation

ElemMatch()

Projection & storages::mongo::options::Projection::ElemMatch	(	std::string_view	field,
		const formats::bson::Document &	pred )

Matches the first element of an array satisfying a predicate.

Parameters

field	name of the array to search
pred	predicate to apply to elements

Note

Array field will be absent from the result if no elements match.

Empty document as a predicate will only match empty documents.

Exclude()

Projection & storages::mongo::options::Projection::Exclude

(

std::string_view

field

)

Excludes a field from the projection.

Warning

Projection cannot have a mix of inclusion and exclusion. Only the _id field can always be excluded.

Slice()

Projection & storages::mongo::options::Projection::Slice	(	std::string_view	field,
		int32_t	limit,
		int32_t	skip = 0 )

Setups an array slice in the projection.

Parameters

field	name of the array field to slice
limit	the number of items to return
skip	the following number of items

Note

skip can be negative, this corresponds to counting from the end backwards.

limit < 0, skip == 0 is equivalent to ‘limit’ = -limit, skip' = limit`.

Warning

Cannot be applied to views.

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The documentation for this class was generated from the following file:

• userver/storages/mongo/options.hpp