Reference to a field in a result set. More...

#include <field.hxx>

Inheritance diagram for pqxx::field:

Public Types
using	size_type = field_size_type

Public Member Functions
	field (const row &R, row_size_type C) noexcept
	Constructor. More...

template<>
bool	to (const char *&Obj) const
	Specialization: `to(const char *&)`. More...

Comparison
bool	operator== (const field &) const
	Byte-by-byte comparison of two fields (all nulls are considered equal) More...

bool	operator!= (const field &rhs) const
	Byte-by-byte comparison (all nulls are considered equal) More...

Column information
const char *	name () const
	Column name. More...

oid	type () const
	Column type. More...

oid	table () const
	What table did this column come from? More...

row_size_type	num () const

row_size_type	table_column () const
	What column number in its originating table did this column come from? More...

Content access
const char *	c_str () const
	Read as plain C string. More...

bool	is_null () const noexcept
	Is this field's value null? More...

size_type	size () const noexcept
	Return number of bytes taken up by the field's value. More...

template<typename T >
auto	to (T &Obj) const -> typename std::enable_if<(not std::is_pointer< T >::value or std::is_same< T, const char *>::value), bool >::type
	Read value into Obj; or leave Obj untouched and return `false` if null. More...

template<typename T >
bool	operator>> (T &Obj) const
	Read value into Obj; or leave Obj untouched and return `false` if null. More...

template<typename T >
auto	to (T &Obj, const T &Default) const -> typename std::enable_if<(not std::is_pointer< T >::value or std::is_same< T, const char *>::value), bool >::type
	Read value into Obj; or use Default & return `false` if null. More...

template<typename T >
T	as (const T &Default) const
	Return value as object of given type, or Default if null. More...

template<typename T >
T	as () const
	Return value as object of given type, or throw exception if null. More...

template<typename T , template< typename > class O>
constexpr O< T >	get () const
	Return value wrapped in some optional type (empty for nulls) More...

array_parser	as_array () const
	Parse the field as an SQL array. More...

Protected Member Functions
const result &	home () const noexcept

size_t	idx () const noexcept

row_size_type	col () const noexcept

Protected Attributes
long	m_col

Detailed Description

Reference to a field in a result set.

A field represents one entry in a row. It represents an actual value in the result set, and can be converted to various types.

Member Typedef Documentation

◆ size_type

using pqxx::field::size_type = field_size_type

Constructor & Destructor Documentation

◆ field()

pqxx::field::field	(	const row &	R,
		row_size_type	C
	)

noexcept

Constructor.

Create field as reference to a field in a result set.

Parameters

R	Row that this field is part of.
C	Column number of this field.

Implementation of the pqxx::field class.

pqxx::field refers to a field in a query result.

See COPYING for copyright license. If you did not receive a file called COPYING with this source code, please notify the distributor of this mistake, or contact the author.

Member Function Documentation

◆ as() [1/2]

template<typename T >

T pqxx::field::as ( const T & Default ) const

Return value as object of given type, or Default if null.

Note that unless the function is instantiated with an explicit template argument, the Default value's type also determines the result type.

◆ as() [2/2]

template<typename T >

T pqxx::field::as ( ) const

Return value as object of given type, or throw exception if null.

Use as as<std::optional<int>>() or as<my_untemplated_optional_t>() as an alternative to get<int>(); this is disabled for use with raw pointers (other than C-strings) because storage for the value can't safely be allocated here

◆ as_array()

array_parser pqxx::field::as_array ( ) const

Parse the field as an SQL array.

Call the parser to retrieve values (and structure) from the array.

Make sure the result object stays alive until parsing is finished. If you keep the row of field object alive, it will keep the result object alive as well.

◆ c_str()

const char * pqxx::field::c_str ( ) const

Read as plain C string.

Since the field's data is stored internally in the form of a zero-terminated C string, this is the fastest way to read it. Use the to() or as() functions to convert the string to other types such as int, or to C++ strings.

References col(), home(), and idx().

Referenced by pqxx::from_string(), pqxx::icursorstream::icursorstream(), pqxx::operator<<(), operator==(), pqxx::pipeline::resume(), pqxx::to_string(), and pqxx::field_streambuf< CHAR, TRAITS >::underflow().

◆ col()

row_size_type pqxx::field::col ( ) const

protectednoexcept

Referenced by c_str(), is_null(), name(), size(), table(), table_column(), and type().

◆ get()

template<typename T , template< typename > class O>

constexpr O<T> pqxx::field::get ( ) const

Return value wrapped in some optional type (empty for nulls)

Use as get<int>() as before to obtain previous behavior (i.e. only usable when std::optional or std::experimental::optional are available), or specify container type with get<int, std::optional>()

◆ home()

const result& pqxx::field::home ( ) const

protectednoexcept

Referenced by c_str(), is_null(), name(), size(), table(), table_column(), and type().

◆ idx()

size_t pqxx::field::idx ( ) const

protectednoexcept

Referenced by c_str(), is_null(), and size().

◆ is_null()

bool pqxx::field::is_null ( ) const

noexcept

Is this field's value null?

References col(), home(), and idx().

Referenced by operator==().

◆ name()

const char * pqxx::field::name ( ) const

Column name.

References col(), pqxx::result::column_name(), and home().

◆ num()

row_size_type pqxx::field::num ( ) const

Referenced by pqxx::const_row_iterator::operator-().

◆ operator!=()

bool pqxx::field::operator!= ( const field & rhs ) const

Byte-by-byte comparison (all nulls are considered equal)

Warning: See operator==() for important information about this operator

◆ operator==()

bool pqxx::field::operator== ( const field & rhs ) const

Byte-by-byte comparison of two fields (all nulls are considered equal)

Warning: null handling is still open to discussion and change!

Handling of null values differs from that in SQL where a comparison involving a null value yields null, so nulls are never considered equal to one another or even to themselves.

Null handling also probably differs from the closest equivalent in C++, which is the NaN (Not-a-Number) value, a singularity comparable to SQL's null. This is because the builtin == operator demands that a == a.

The usefulness of this operator is questionable. No interpretation whatsoever is imposed on the data; 0 and 0.0 are considered different, as are null vs. the empty string, or even different (but possibly equivalent and equally valid) encodings of the same Unicode character etc.

References c_str(), is_null(), and size().

◆ operator>>()

template<typename T >

bool pqxx::field::operator>> ( T & Obj ) const

Read value into Obj; or leave Obj untouched and return false if null.

◆ size()

pqxx::field::size_type pqxx::field::size ( ) const

noexcept

Return number of bytes taken up by the field's value.

Includes the terminating zero byte.

References col(), home(), and idx().

Referenced by pqxx::from_string(), pqxx::operator<<(), operator==(), pqxx::to_string(), and pqxx::field_streambuf< CHAR, TRAITS >::underflow().

◆ table()

pqxx::oid pqxx::field::table ( ) const

What table did this column come from?

References col(), pqxx::result::column_table(), and home().

◆ table_column()

pqxx::row::size_type pqxx::field::table_column ( ) const

What column number in its originating table did this column come from?

References col(), home(), and pqxx::result::table_column().

◆ to() [1/3]

template<typename T >

auto pqxx::field::to ( T & Obj ) const -> typename std::enable_if<( not std::is_pointer<T>::value or std::is_same<T, const char*>::value ), bool>::type

Read value into Obj; or leave Obj untouched and return false if null.

Note this can be used with optional types (except pointers other than C-strings)

References pqxx::from_string().

◆ to() [2/3]

template<typename T >

auto pqxx::field::to	(	T &	Obj,
		const T &	Default
	)		const -> typename std::enable_if<( not std::is_pointer<T>::value or std::is_same<T, const char*>::value ), bool>::type

Read value into Obj; or use Default & return false if null.

Note this can be used with optional types (except pointers other than C-strings)

◆ to() [3/3]

template<>

bool pqxx::field::to ( const char *& Obj ) const

Specialization: to(const char *&).

The buffer has the same lifetime as the data in this result (i.e. of this result object, or the last remaining one copied from it etc.), so take care not to use it after the last result object referring to this query result is destroyed.

◆ type()

pqxx::oid pqxx::field::type ( ) const

Column type.

References col(), pqxx::result::column_type(), and home().

Member Data Documentation

◆ m_col

long pqxx::field::m_col

protected

You'd expect this to be a size_t, but due to the way reverse iterators are related to regular iterators, it must be allowed to underflow to -1.

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

field.hxx
field.cxx

Public Types

Public Member Functions

Protected Member Functions

Protected Attributes

Detailed Description

Member Typedef Documentation

◆ size_type

Constructor & Destructor Documentation

◆ field()

Member Function Documentation

◆ as() [1/2]

◆ as() [2/2]

◆ as_array()

◆ c_str()

◆ col()

◆ get()

◆ home()

◆ idx()

◆ is_null()

◆ name()

◆ num()

◆ operator!=()

◆ operator==()

◆ operator>>()

◆ size()

◆ table()

◆ table_column()

◆ to() [1/3]

◆ to() [2/3]

◆ to() [3/3]

◆ type()

Member Data Documentation

◆ m_col