libpqxx 7.7.5
stream_to.hxx
1/* Definition of the pqxx::stream_to class.
2 *
3 * pqxx::stream_to enables optimized batch updates to a database table.
4 *
5 * DO NOT INCLUDE THIS FILE DIRECTLY; include pqxx/stream_to.hxx instead.
6 *
7 * Copyright (c) 2000-2023, 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_STREAM_TO
14#define PQXX_H_STREAM_TO
15
16#if !defined(PQXX_HEADER_PRE)
17# error "Include libpqxx headers as <pqxx/header>, not <pqxx/header.hxx>."
18#endif
19
20#include "pqxx/separated_list.hxx"
21#include "pqxx/transaction_base.hxx"
22
23
24namespace pqxx
25{
27
80class PQXX_LIBEXPORT stream_to : transaction_focus
81{
82public:
84
105 transaction_base &tx, std::string_view path, std::string_view columns = "")
106 {
107 return {tx, path, columns};
108 }
109
111
122 std::initializer_list<std::string_view> columns = {})
123 {
124 auto const &conn{tx.conn()};
125 return raw_table(tx, conn.quote_table(path), conn.quote_columns(columns));
126 }
127
128#if defined(PQXX_HAVE_CONCEPTS)
130
137 template<PQXX_CHAR_STRINGS_ARG COLUMNS>
138 static stream_to
139 table(transaction_base &tx, table_path path, COLUMNS const &columns)
140 {
141 auto const &conn{tx.conn()};
142 return stream_to::raw_table(
143 tx, conn.quote_table(path), tx.conn().quote_columns(columns));
144 }
145
147
154 template<PQXX_CHAR_STRINGS_ARG COLUMNS>
155 static stream_to
156 table(transaction_base &tx, std::string_view path, COLUMNS const &columns)
157 {
158 return stream_to::raw_table(tx, path, tx.conn().quote_columns(columns));
159 }
160#endif // PQXX_HAVE_CONCEPTS
161
163
172 [[deprecated("Use table() or raw_table() factory.")]] stream_to(
173 transaction_base &tx, std::string_view table_name) :
174 stream_to{tx, table_name, ""sv}
175 {}
176
178
180 template<typename Columns>
181 [[deprecated("Use table() or raw_table() factory.")]] stream_to(
182 transaction_base &, std::string_view table_name, Columns const &columns);
183
185
187 template<typename Iter>
188 [[deprecated("Use table() or raw_table() factory.")]] stream_to(
189 transaction_base &, std::string_view table_name, Iter columns_begin,
190 Iter columns_end);
191
192 ~stream_to() noexcept;
193
195 [[nodiscard]] constexpr operator bool() const noexcept
196 {
197 return not m_finished;
198 }
200 [[nodiscard]] constexpr bool operator!() const noexcept
201 {
202 return m_finished;
203 }
204
206
212 void complete();
213
215
224 template<typename Row> stream_to &operator<<(Row const &row)
225 {
226 write_row(row);
227 return *this;
228 }
229
231
236
238
244 template<typename Row> void write_row(Row const &row)
245 {
246 fill_buffer(row);
247 write_buffer();
248 }
249
251
254 template<typename... Ts> void write_values(Ts const &...fields)
255 {
256 fill_buffer(fields...);
257 write_buffer();
258 }
259
260private:
262 stream_to(
263 transaction_base &tx, std::string_view path, std::string_view columns);
264
265 bool m_finished = false;
266
268 std::string m_buffer;
269
271 std::string m_field_buf;
272
274 internal::glyph_scanner_func *m_scanner;
275
277 void write_raw_line(std::string_view);
278
280
282 void write_buffer();
283
285 static constexpr std::string_view null_field{"\\N\t"};
286
288 template<typename T>
289 static std::enable_if_t<nullness<T>::always_null, std::size_t>
290 estimate_buffer(T const &)
291 {
292 return std::size(null_field);
293 }
294
296
299 template<typename T>
300 static std::enable_if_t<not nullness<T>::always_null, std::size_t>
301 estimate_buffer(T const &field)
302 {
303 return is_null(field) ? std::size(null_field) : size_buffer(field);
304 }
305
307 void escape_field_to_buffer(std::string_view data);
308
310
316 template<typename Field>
317 std::enable_if_t<not nullness<Field>::always_null>
318 append_to_buffer(Field const &f)
319 {
320 // We append each field, terminated by a tab. That will leave us with
321 // one tab too many, assuming we write any fields at all; we remove that
322 // at the end.
323 if (is_null(f))
324 {
325 // Easy. Append null and tab in one go.
326 m_buffer.append(null_field);
327 }
328 else
329 {
330 // Convert f into m_buffer.
331
332 using traits = string_traits<Field>;
333 auto const budget{estimate_buffer(f)};
334 auto const offset{std::size(m_buffer)};
335
336 if constexpr (std::is_arithmetic_v<Field>)
337 {
338 // Specially optimised for "safe" types, which never need any
339 // escaping. Convert straight into m_buffer.
340
341 // The budget we get from size_buffer() includes room for the trailing
342 // zero, which we must remove. But we're also inserting tabs between
343 // fields, so we re-purpose the extra byte for that.
344 auto const total{offset + budget};
345 m_buffer.resize(total);
346 auto const data{m_buffer.data()};
347 char *const end{traits::into_buf(data + offset, data + total, f)};
348 *(end - 1) = '\t';
349 // Shrink to fit. Keep the tab though.
350 m_buffer.resize(static_cast<std::size_t>(end - data));
351 }
352 else if constexpr (
353 std::is_same_v<Field, std::string> or
354 std::is_same_v<Field, std::string_view> or
355 std::is_same_v<Field, zview>)
356 {
357 // This string may need escaping.
358 m_field_buf.resize(budget);
359 escape_field_to_buffer(f);
360 }
361 else
362 {
363 // This field needs to be converted to a string, and after that,
364 // escaped as well.
365 m_field_buf.resize(budget);
366 auto const data{m_field_buf.data()};
367 escape_field_to_buffer(
368 traits::to_buf(data, data + std::size(m_field_buf), f));
369 }
370 }
371 }
372
374
380 template<typename Field>
381 std::enable_if_t<nullness<Field>::always_null>
382 append_to_buffer(Field const &)
383 {
384 m_buffer.append(null_field);
385 }
386
388 template<typename Container>
389 std::enable_if_t<not std::is_same_v<typename Container::value_type, char>>
390 fill_buffer(Container const &c)
391 {
392 // To avoid unnecessary allocations and deallocations, we run through c
393 // twice: once to determine how much buffer space we may need, and once to
394 // actually write it into the buffer.
395 std::size_t budget{0};
396 for (auto const &f : c) budget += estimate_buffer(f);
397 m_buffer.reserve(budget);
398 for (auto const &f : c) append_to_buffer(f);
399 }
400
402 template<typename Tuple, std::size_t... indexes>
403 static std::size_t
404 budget_tuple(Tuple const &t, std::index_sequence<indexes...>)
405 {
406 return (estimate_buffer(std::get<indexes>(t)) + ...);
407 }
408
410 template<typename Tuple, std::size_t... indexes>
411 void append_tuple(Tuple const &t, std::index_sequence<indexes...>)
412 {
413 (append_to_buffer(std::get<indexes>(t)), ...);
414 }
415
417 template<typename... Elts> void fill_buffer(std::tuple<Elts...> const &t)
418 {
419 using indexes = std::make_index_sequence<sizeof...(Elts)>;
420
421 m_buffer.reserve(budget_tuple(t, indexes{}));
422 append_tuple(t, indexes{});
423 }
424
426 template<typename... Ts> void fill_buffer(const Ts &...fields)
427 {
428 (..., append_to_buffer(fields));
429 }
430
431 constexpr static std::string_view s_classname{"stream_to"};
432};
433
434
435template<typename Columns>
437 transaction_base &tx, std::string_view table_name, Columns const &columns) :
438 stream_to{tx, table_name, std::begin(columns), std::end(columns)}
439{}
440
441
442template<typename Iter>
444 transaction_base &tx, std::string_view table_name, Iter columns_begin,
445 Iter columns_end) :
446 stream_to{
447 tx,
448 tx.quote_name(
449 table_name,
450 separated_list(",", columns_begin, columns_end, [&tx](auto col) {
451 return tx.quote_name(*col);
452 }))}
453{}
454} // namespace pqxx
455#endif
The home of all libpqxx classes, functions, templates, etc.
Definition array.hxx: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:495
std::string separated_list(std::string_view sep, ITER begin, ITER end, ACCESS access)
Represent sequence of values as a string, joined by a given separator.
Definition separated_list.hxx:43
std::size_t size_buffer(TYPE const &...value) noexcept
Estimate how much buffer space is needed to represent values as a string.
Definition strconv.hxx:381
std::initializer_list< std::string_view > table_path
Representation of a PostgreSQL table path.
Definition connection.hxx:123
constexpr bool is_null(TYPE const &value) noexcept
Is value null?
Definition strconv.hxx:370
Reference to one row in a result.
Definition row.hxx:47
Stream data from the database.
Definition stream_from.hxx:78
Efficiently write data directly to a database table.
Definition stream_to.hxx:81
static stream_to raw_table(transaction_base &tx, std::string_view path, std::string_view columns="")
Stream data to a pre-quoted table and columns.
Definition stream_to.hxx:104
constexpr bool operator!() const noexcept
Has this stream been through its concluding complete()?
Definition stream_to.hxx:200
static stream_to table(transaction_base &tx, table_path path, std::initializer_list< std::string_view > columns={})
Create a stream_to writing to a named table and columns.
Definition stream_to.hxx:120
void write_values(Ts const &...fields)
Insert values as a row.
Definition stream_to.hxx:254
stream_to(transaction_base &tx, std::string_view table_name)
Create a stream, without specifying columns.
Definition stream_to.hxx:172
stream_to & operator<<(Row const &row)
Insert a row of data.
Definition stream_to.hxx:224
void write_row(Row const &row)
Insert a row of data, given in the form of a std::tuple or container.
Definition stream_to.hxx:244
Interface definition (and common code) for "transaction" classes.
Definition transaction_base.hxx:77
constexpr connection & conn() const noexcept
The connection in which this transaction lives.
Definition transaction_base.hxx:769
std::string quote_name(std::string_view identifier) const
Escape an SQL identifier for use in a query.
Definition transaction_base.hxx:220
Base class for things that monopolise a transaction's attention.
Definition transaction_focus.hxx:29