storages::postgres::ParameterStore Class Reference

Table of Contents

• Public Member Functions
• Detailed Description
• Member Function Documentation
• IsEmpty()
• PushBack()
• Size()

Class for dynamic PostgreSQL parameter list construction. More...

#include <userver/storages/postgres/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.

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.

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