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 46 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 49 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