storages::postgres::ParameterStore Class Reference

#include <userver/storages/postgres/parameter_store.hpp>

Detailed Description

Class for dynamic PostgreSQL parameter list construction.

Typical use case for this container is to keep parameters around while the query is being constructed on the fly:

template <class ConnectionPtr>
auto ParameterStoreSample(
    const ConnectionPtr& conn,
    std::optional<int> a = {},
    std::optional<int> b = {},
    std::optional<int> c = {},
    std::optional<int> d = {},
    std::optional<int> e = {}
) {
    storages::postgres::ParameterStore parameters;
    std::string filter;
 
    auto append_if_has_value = [&](std::string_view name, const auto& value) {
        if (value) {
            auto separator = (parameters.IsEmpty() ? std::string_view{} : " AND ");
            parameters.PushBack(*value);
 
            // Do NOT put parameters directly into the query! It leads to
            // vulnerabilities and bad performance.
            filter += fmt::format("{}{}=${}", separator, name, parameters.Size());
        }
    };
 
    append_if_has_value("a", a);
    append_if_has_value("b", b);
    append_if_has_value("c", c);
    append_if_has_value("d", d);
    append_if_has_value("e", e);
 
    if (parameters.IsEmpty()) {
        throw std::runtime_error("No filters provided");
    }
 
    return conn->Execute("SELECT x FROM some_table WHERE " + filter, parameters);
}

Note that storages::postgres::Cluster::Execute with explicitly provided arguments works slightly faster:

std::size_t InsertSomeKey(storages::postgres::Cluster& pg, std::string_view key) {
    auto res = pg.Execute(storages::postgres::ClusterHostType::kMaster, "INSERT INTO keys VALUES ($1)", key);
    return res.RowsAffected();
}

Definition at line 26 of file parameter_store.hpp.

Public Member Functions
	ParameterStore (const ParameterStore &)=delete
	ParameterStore (ParameterStore &&)=default
ParameterStore &	operator= (const ParameterStore &)=delete
ParameterStore &	operator= (ParameterStore &&)=default
template<typename T >
ParameterStore &	PushBack (const T &param)
	Adds a parameter to the end of the parameter list.
bool	IsEmpty () const
	Returns whether the parameter list is empty.
size_t	Size () const
	Returns current size of the list.

Member Function Documentation

IsEmpty()

bool storages::postgres::ParameterStore::IsEmpty ( ) const

inline

Returns whether the parameter list is empty.

Definition at line 47 of file parameter_store.hpp.

PushBack()

template<typename T >

ParameterStore & storages::postgres::ParameterStore::PushBack ( const T & param )

inline

Adds a parameter to the end of the parameter list.

Note

Currently only built-in/system types are supported.

Definition at line 37 of file parameter_store.hpp.

Size()

size_t storages::postgres::ParameterStore::Size ( ) const

inline

Returns current size of the list.

Definition at line 50 of file parameter_store.hpp.

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

• userver/storages/postgres/parameter_store.hpp