libpqxx 7.8.1
stream_from.hxx
1/* Definition of the pqxx::stream_from class.
2 *
3 * pqxx::stream_from enables optimized batch reads from a database table.
4 *
5 * DO NOT INCLUDE THIS FILE DIRECTLY; include pqxx/stream_from 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_FROM
14#define PQXX_H_STREAM_FROM
15
16#if !defined(PQXX_HEADER_PRE)
17# error "Include libpqxx headers as <pqxx/header>, not <pqxx/header.hxx>."
18#endif
19
20#include <cassert>
21#include <variant>
22
23#include "pqxx/connection.hxx"
24#include "pqxx/except.hxx"
25#include "pqxx/internal/concat.hxx"
26#include "pqxx/internal/encoding_group.hxx"
27#include "pqxx/internal/stream_iterator.hxx"
28#include "pqxx/separated_list.hxx"
29#include "pqxx/transaction_focus.hxx"
30
31
32namespace pqxx
33{
34class transaction_base;
35
36
38
42
45
46
48
78class PQXX_LIBEXPORT stream_from : transaction_focus
79{
80public:
81 using raw_line =
82 std::pair<std::unique_ptr<char, void (*)(void const *)>, std::size_t>;
83
86
88
97 [[deprecated("Use transaction_base::stream instead.")]] static stream_from
98 query(transaction_base &tx, std::string_view q)
99 {
100#include "pqxx/internal/ignore-deprecated-pre.hxx"
101 return {tx, from_query, q};
102#include "pqxx/internal/ignore-deprecated-post.hxx"
103 }
104
115
117
133 [[deprecated("Use transaction_base::stream instead.")]] static stream_from
134 raw_table(
135 transaction_base &tx, std::string_view path,
136 std::string_view columns = ""sv);
137
139
141 [[deprecated("Use transaction_base::stream instead.")]] static stream_from
142 table(
144 std::initializer_list<std::string_view> columns = {});
146
148
150 [[deprecated("Use transaction_base::stream instead.")]] stream_from(
151 transaction_base &, from_query_t, std::string_view query);
152
154
156 [[deprecated("Use transaction_base::stream instead.")]] stream_from(
157 transaction_base &, from_table_t, std::string_view table);
158
160
162 template<typename Iter>
163 [[deprecated("Use transaction_base::stream instead.")]] stream_from(
164 transaction_base &, from_table_t, std::string_view table,
165 Iter columns_begin, Iter columns_end);
166
168
170 template<typename Columns>
171 [[deprecated("Use transaction_base::stream() instead.")]] stream_from(
172 transaction_base &tx, from_table_t, std::string_view table,
173 Columns const &columns);
174
175#include "pqxx/internal/ignore-deprecated-pre.hxx"
177 [[deprecated("Use transaction_base::stream instead.")]] stream_from(
178 transaction_base &tx, std::string_view table) :
179 stream_from{tx, from_table, table}
180 {}
181#include "pqxx/internal/ignore-deprecated-post.hxx"
182
184 template<typename Columns>
185 [[deprecated("Use transaction_base::stream instead.")]] stream_from(
186 transaction_base &tx, std::string_view table, Columns const &columns) :
187 stream_from{tx, from_table, table, columns}
188 {}
189
191 template<typename Iter>
192 [[deprecated("Use transaction_base::stream instead.")]] stream_from(
193 transaction_base &, std::string_view table, Iter columns_begin,
194 Iter columns_end);
195
196 ~stream_from() noexcept;
197
199 [[nodiscard]] constexpr operator bool() const noexcept
200 {
201 return not m_finished;
202 }
204 [[nodiscard]] constexpr bool operator!() const noexcept
205 {
206 return m_finished;
207 }
208
210
216 void complete();
217
219
226 template<typename Tuple> stream_from &operator>>(Tuple &);
227
229 template<typename... Vs>
230 stream_from &operator>>(std::variant<Vs...> &) = delete;
231
233
237 template<typename... TYPE> [[nodiscard]] auto iter() &
238 {
239 return pqxx::internal::stream_input_iteration<TYPE...>{*this};
240 }
241
243
259 std::vector<zview> const *read_row() &;
260
262
263 raw_line get_raw_line();
264
265private:
266 // TODO: Clean up this signature once we cull the deprecated constructors.
269 transaction_base &tx, std::string_view table, std::string_view columns,
271
272 // TODO: Clean up this signature once we cull the deprecated constructors.
275 transaction_base &, std::string_view unquoted_table,
276 std::string_view columns, from_table_t, int);
277
278 template<typename Tuple, std::size_t... indexes>
279 void extract_fields(Tuple &t, std::index_sequence<indexes...>) const
280 {
281 (extract_value<Tuple, indexes>(t), ...);
282 }
283
284 pqxx::internal::char_finder_func *m_char_finder;
285
287 std::string m_row;
288
290 std::vector<zview> m_fields;
291
292 bool m_finished = false;
293
294 void close();
295
296 template<typename Tuple, std::size_t index>
297 void extract_value(Tuple &) const;
298
300 void parse_line();
301};
302
303
304template<typename Columns>
306 transaction_base &tx, from_table_t, std::string_view table_name,
307 Columns const &columns) :
309 tx, from_table, table_name, std::begin(columns), std::end(columns)}
310{}
311
312
313template<typename Iter>
315 transaction_base &tx, from_table_t, std::string_view table,
316 Iter columns_begin, Iter columns_end) :
318 tx, table, separated_list(",", columns_begin, columns_end),
319 from_table, 1}
320{}
321
322
323template<typename Tuple> inline stream_from &stream_from::operator>>(Tuple &t)
324{
325 if (m_finished)
326 PQXX_UNLIKELY return *this;
327 static constexpr auto tup_size{std::tuple_size_v<Tuple>};
328 m_fields.reserve(tup_size);
329 parse_line();
330 if (m_finished)
331 PQXX_UNLIKELY return *this;
332
333 if (std::size(m_fields) != tup_size)
334 throw usage_error{internal::concat(
335 "Tried to extract ", tup_size, " field(s) from a stream of ",
336 std::size(m_fields), ".")};
337
338 extract_fields(t, std::make_index_sequence<tup_size>{});
339 return *this;
340}
341
342
343template<typename Tuple, std::size_t index>
344inline void stream_from::extract_value(Tuple &t) const
345{
346 using field_type = strip_t<decltype(std::get<index>(t))>;
347 using nullity = nullness<field_type>;
348 assert(index < std::size(m_fields));
349 if constexpr (nullity::always_null)
350 {
351 if (std::data(m_fields[index]) != nullptr)
352 throw conversion_error{"Streaming non-null value into null field."};
353 }
354 else if (std::data(m_fields[index]) == nullptr)
355 {
356 if constexpr (nullity::has_null)
357 std::get<index>(t) = nullity::null();
358 else
359 internal::throw_null_conversion(type_name<field_type>);
360 }
361 else
362 {
363 // Don't ever try to convert a non-null value to nullptr_t!
364 std::get<index>(t) = from_string<field_type>(m_fields[index]);
365 }
366}
367} // namespace pqxx
368#endif
The home of all libpqxx classes, functions, templates, etc.
Definition array.hxx:33
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:44
std::remove_cv_t< std::remove_reference_t< TYPE > > strip_t
Remove any constness, volatile, and reference-ness from a type.
Definition types.hxx:91
constexpr from_query_t from_query
Pass this to a stream_from constructor to stream query results.
Definition stream_from.hxx:44
constexpr from_table_t from_table
Pass this to a stream_from constructor to stream table contents.
Definition stream_from.hxx:40
std::initializer_list< std::string_view > table_path
Representation of a PostgreSQL table path.
Definition connection.hxx:188
void PQXX_COLD throw_null_conversion(std::string const &type)
Definition strconv.cxx:253
Error in usage of libpqxx library, similar to std::logic_error.
Definition except.hxx:249
Value conversion failed, e.g. when converting "Hello" to int.
Definition except.hxx:283
Traits describing a type's "null value," if any.
Definition strconv.hxx:93
Stream data from the database.
Definition stream_from.hxx:79
static stream_from query(transaction_base &tx, std::string_view q)
Factory: Execute query, and stream the results.
Definition stream_from.hxx:98
stream_from & operator>>(std::variant< Vs... > &)=delete
Doing this with a std::variant is going to be horrifically borked.
stream_from & operator>>(Tuple &)
Read one row into a tuple.
Definition stream_from.hxx:323
stream_from(transaction_base &tx, std::string_view table, Columns const &columns)
Definition stream_from.hxx:185
std::pair< std::unique_ptr< char, void(*)(void const *)>, std::size_t > raw_line
Definition stream_from.hxx:82
stream_from(stream_from &&)=delete
stream_from(transaction_base &, std::string_view table, Iter columns_begin, Iter columns_end)
stream_from & operator=(stream_from &&)=delete
stream_from(transaction_base &tx, std::string_view table)
Definition stream_from.hxx:177
auto iter() &
Iterate over this stream. Supports range-based "for" loops.
Definition stream_from.hxx:237
constexpr bool operator!() const noexcept
Has this stream produced all the data it is going to produce?
Definition stream_from.hxx:204
Interface definition (and common code) for "transaction" classes.
Definition transaction_base.hxx:88
Base class for things that monopolise a transaction's attention.
Definition transaction_focus.hxx:29
Marker for stream_from constructors: "stream from table.".
Definition types.hxx:68
Marker for stream_from constructors: "stream from query.".
Definition types.hxx:74