libpqxx
The C++ client library for PostgreSQL
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field.hxx
1/* Definitions for the pqxx::field class.
2 *
3 * pqxx::field refers to a field in a query result.
4 *
5 * DO NOT INCLUDE THIS FILE DIRECTLY; include pqxx/field instead.
6 *
7 * Copyright (c) 2000-2024, Jeroen T. Vermeulen.
8 *
9 * See COPYING for copyright license. If you did not receive a file called
10 * COPYING with this source code, please notify the distributor of this
11 * mistake, or contact the author.
12 */
13#ifndef PQXX_H_FIELD
14#define PQXX_H_FIELD
15
16#if !defined(PQXX_HEADER_PRE)
17# error "Include libpqxx headers as <pqxx/header>, not <pqxx/header.hxx>."
18#endif
19
20#include <optional>
21
22#include "pqxx/array.hxx"
23#include "pqxx/composite.hxx"
24#include "pqxx/result.hxx"
25#include "pqxx/strconv.hxx"
26#include "pqxx/types.hxx"
27
28namespace pqxx
29{
31
34class PQXX_LIBEXPORT field
35{
36public:
37 using size_type = field_size_type;
38
44
60 [[nodiscard]] PQXX_PURE bool operator==(field const &) const noexcept;
61
63
65 [[nodiscard]] PQXX_PURE bool operator!=(field const &rhs) const noexcept
66 {
67 return not operator==(rhs);
68 }
70
76 [[nodiscard]] PQXX_PURE char const *name() const &;
77
79 [[nodiscard]] oid PQXX_PURE type() const;
80
82 [[nodiscard]] PQXX_PURE oid table() const;
83
85 PQXX_PURE constexpr row_size_type num() const noexcept { return col(); }
86
88 [[nodiscard]] PQXX_PURE row_size_type table_column() const;
90
107
111 [[nodiscard]] PQXX_PURE std::string_view view() const &
112 {
113 return std::string_view(c_str(), size());
114 }
115
117
126 [[nodiscard]] PQXX_PURE char const *c_str() const &;
127
129 [[nodiscard]] PQXX_PURE bool is_null() const noexcept;
130
132 [[nodiscard]] PQXX_PURE size_type size() const noexcept;
133
135
138 template<typename T>
139 auto to(T &obj) const ->
140 typename std::enable_if_t<
141 (not std::is_pointer<T>::value or std::is_same<T, char const *>::value),
142 bool>
143 {
144 if (is_null())
145 {
146 return false;
147 }
148 else
149 {
150 auto const data{c_str()};
151 from_string(data, obj);
152 return true;
153 }
154 }
155
157
162 template<typename... T> bool composite_to(T &...fields) const
163 {
164 if (is_null())
165 {
166 return false;
167 }
168 else
169 {
170 parse_composite(m_home.m_encoding, view(), fields...);
171 return true;
172 }
173 }
174
176 template<typename T> bool operator>>(T &obj) const { return to(obj); }
177
179
189 template<typename T>
190 auto to(T &obj, T const &default_value) const ->
191 typename std::enable_if_t<
192 (not std::is_pointer<T>::value or std::is_same<T, char const *>::value),
193 bool>
194 {
195 bool const null{is_null()};
196 if (null)
197 obj = default_value;
198 else
199 obj = from_string<T>(this->view());
200 return not null;
201 }
202
204
207 template<typename T> T as(T const &default_value) const
208 {
209 if (is_null())
210 return default_value;
211 else
212 return from_string<T>(this->view());
213 }
214
216
221 template<typename T> T as() const
222 {
223 if (is_null())
224 {
225 if constexpr (not nullness<T>::has_null)
226 internal::throw_null_conversion(type_name<T>);
227 else
228 return nullness<T>::null();
229 }
230 else
231 {
232 return from_string<T>(this->view());
233 }
234 }
235
237
240 template<typename T, template<typename> class O = std::optional>
241 constexpr O<T> get() const
242 {
243 return as<O<T>>();
244 }
245
247 template<typename ELEMENT, auto... ARGS>
248 array<ELEMENT, ARGS...> as_sql_array() const
249 {
250 using array_type = array<ELEMENT, ARGS...>;
251
252 // There's no such thing as a null SQL array.
253 if (is_null())
254 internal::throw_null_conversion(type_name<array_type>);
255 else
256 return array_type{this->view(), this->m_home.m_encoding};
257 }
258
260
266 [[deprecated(
267 "Avoid pqxx::array_parser. "
268 "Instead, use as_sql_array() to convert to pqxx::array.")]]
269 array_parser as_array() const & noexcept
270 {
271 return array_parser{c_str(), m_home.m_encoding};
272 }
274
276
280 [[deprecated(
281 "Do not construct fields yourself. Get them from the row.")]] field(row const &r, row_size_type c) noexcept;
282
284 [[deprecated(
285 "Do not construct fields yourself. Get them from the "
286 "row.")]] field() noexcept = default;
287
288
289protected:
290 constexpr result const &home() const noexcept { return m_home; }
291 constexpr result::size_type idx() const noexcept { return m_row; }
292 constexpr row_size_type col() const noexcept { return m_col; }
293
294 // TODO: Create gates.
295 friend class pqxx::result;
296 friend class pqxx::row;
297 field(
298 result const &r, result_size_type row_num, row_size_type col_num) noexcept
299 :
300 m_col{col_num}, m_home{r}, m_row{row_num}
301 {}
302
307 row_size_type m_col;
308
309private:
310 result m_home;
311 result::size_type m_row;
312};
313
314
315template<> inline bool field::to<std::string>(std::string &obj) const
316{
317 bool const null{is_null()};
318 if (not null)
319 obj = std::string{view()};
320 return not null;
321}
322
323
324template<>
325inline bool field::to<std::string>(
326 std::string &obj, std::string const &default_value) const
327{
328 bool const null{is_null()};
329 if (null)
331 else
332 obj = std::string{view()};
333 return not null;
334}
335
336
338
343template<> inline bool field::to<char const *>(char const *&obj) const
344{
345 bool const null{is_null()};
346 if (not null)
347 obj = c_str();
348 return not null;
349}
350
351
352template<> inline bool field::to<std::string_view>(std::string_view &obj) const
353{
354 bool const null{is_null()};
355 if (not null)
356 obj = view();
357 return not null;
358}
359
360
361template<>
362inline bool field::to<std::string_view>(
363 std::string_view &obj, std::string_view const &default_value) const
364{
365 bool const null{is_null()};
366 if (null)
368 else
369 obj = view();
370 return not null;
371}
372
373
374template<> inline std::string_view field::as<std::string_view>() const
375{
376 if (is_null())
377 PQXX_UNLIKELY
379 return view();
380}
381
382
383template<>
384inline std::string_view
385field::as<std::string_view>(std::string_view const &default_value) const
386{
387 return is_null() ? default_value : view();
388}
389
390
391template<> inline bool field::to<zview>(zview &obj) const
392{
393 bool const null{is_null()};
394 if (not null)
395 obj = zview{c_str(), size()};
396 return not null;
397}
398
399
400template<>
401inline bool field::to<zview>(zview &obj, zview const &default_value) const
402{
403 bool const null{is_null()};
404 if (null)
406 else
407 obj = zview{c_str(), size()};
408 return not null;
409}
410
411
412template<> inline zview field::as<zview>() const
413{
414 if (is_null())
415 PQXX_UNLIKELY
417 return zview{c_str(), size()};
418}
419
420
421template<> inline zview field::as<zview>(zview const &default_value) const
422{
423 return is_null() ? default_value : zview{c_str(), size()};
424}
425
426
427template<typename CHAR = char, typename TRAITS = std::char_traits<CHAR>>
428class field_streambuf : public std::basic_streambuf<CHAR, TRAITS>
429{
430public:
431 using char_type = CHAR;
432 using traits_type = TRAITS;
433 using int_type = typename traits_type::int_type;
434 using pos_type = typename traits_type::pos_type;
435 using off_type = typename traits_type::off_type;
436 using openmode = std::ios::openmode;
437 using seekdir = std::ios::seekdir;
438
439 explicit field_streambuf(field const &f) : m_field{f} { initialize(); }
440
441protected:
442 virtual int sync() override { return traits_type::eof(); }
443
444 virtual pos_type seekoff(off_type, seekdir, openmode) override
445 {
446 return traits_type::eof();
447 }
448 virtual pos_type seekpos(pos_type, openmode) override
449 {
450 return traits_type::eof();
451 }
452 virtual int_type overflow(int_type) override { return traits_type::eof(); }
453 virtual int_type underflow() override { return traits_type::eof(); }
454
455private:
456 field const &m_field;
457
458 int_type initialize()
459 {
460 auto g{static_cast<char_type *>(const_cast<char *>(m_field.c_str()))};
461 this->setg(g, g, g + std::size(m_field));
462 return int_type(std::size(m_field));
463 }
464};
465
466
468
481template<typename CHAR = char, typename TRAITS = std::char_traits<CHAR>>
482class basic_fieldstream : public std::basic_istream<CHAR, TRAITS>
483{
484 using super = std::basic_istream<CHAR, TRAITS>;
485
486public:
487 using char_type = CHAR;
488 using traits_type = TRAITS;
489 using int_type = typename traits_type::int_type;
490 using pos_type = typename traits_type::pos_type;
491 using off_type = typename traits_type::off_type;
492
493 [[deprecated("Use field::as<...>() or field::c_str().")]] basic_fieldstream(
494 field const &f) :
495 super{nullptr}, m_buf{f}
496 {
497 super::init(&m_buf);
498 }
499
500private:
502};
503
504
507
508
510
533template<typename CHAR>
534[[deprecated(
535 "Do this by hand, probably with better error checking.")]] inline std::
536 basic_ostream<CHAR> &
537 operator<<(std::basic_ostream<CHAR> &s, field const &value)
538{
539 s.write(value.c_str(), std::streamsize(std::size(value)));
540 return s;
541}
542
543
545
548template<typename T> inline T from_string(field const &value)
549{
550 if (value.is_null())
551 {
552 if constexpr (nullness<T>::has_null)
553 return nullness<T>::null();
554 else
556 }
557 else
558 {
559 return from_string<T>(value.view());
560 }
561}
562
563
565
571template<>
572inline std::nullptr_t from_string<std::nullptr_t>(field const &value)
573{
574 if (not value.is_null())
575 throw conversion_error{
576 "Extracting non-null field into nullptr_t variable."};
577 return nullptr;
578}
579
580
582template<> PQXX_LIBEXPORT std::string to_string(field const &value);
583} // namespace pqxx
584#endif
Input stream that gets its data from a result field.
Definition field.hxx:483
Definition field.hxx:429
Result set containing data returned by a query or command.
Definition result.hxx:92
Marker-type wrapper: zero-terminated std::string_view.
Definition zview.hxx:38
Value conversion failed, e.g. when converting "Hello" to int.
Definition except.hxx:283
void throw_null_conversion(std::string const &type)
Throw exception for attempt to convert SQL NULL to given type.
Definition strconv.cxx:248
The home of all libpqxx classes, functions, templates, etc.
Definition array.cxx:27
std::basic_ostream< CHAR > & operator<<(std::basic_ostream< CHAR > &s, field const &value)
Write a result field to any type of stream.
Definition field.hxx:537
std::size_t field_size_type
Number of bytes in a field of database data.
Definition types.hxx:40
constexpr char array_separator
Element separator between SQL array elements of this type.
Definition strconv.hxx:559
int row_size_type
Number of fields in a row of database data.
Definition types.hxx:34
constexpr bool is_null(TYPE const &value) noexcept
Is value null?
Definition strconv.hxx:515
void parse_composite(pqxx::internal::encoding_group enc, std::string_view text, T &...fields)
Parse a string representation of a value of a composite type.
Definition composite.hxx:35
std::nullptr_t from_string< std::nullptr_t >(field const &value)
Convert a field's value to nullptr_t.
Definition field.hxx:572
T from_string(field const &value)
Convert a field's value to type T.
Definition field.hxx:548
Traits describing a type's "null value," if any.
Definition strconv.hxx:91