libpqxx 7.7.0
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) 2000-2022, 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#include <cassert>
17#include <functional>
18#include <variant>
19
20#include "pqxx/connection.hxx"
21#include "pqxx/except.hxx"
22#include "pqxx/internal/concat.hxx"
23#include "pqxx/internal/encoding_group.hxx"
24#include "pqxx/internal/stream_iterator.hxx"
25#include "pqxx/separated_list.hxx"
26#include "pqxx/transaction_focus.hxx"
27
28
29namespace pqxx
30{
31class transaction_base;
32
33
34// C++20: constinit.
36
39// C++20: constinit.
41
44
45
47
71class PQXX_LIBEXPORT stream_from : transaction_focus
72{
73public:
74 using raw_line =
75 std::pair<std::unique_ptr<char, std::function<void(char *)>>, std::size_t>;
76
78
87 static stream_from query(transaction_base &tx, std::string_view q)
88 {
89#include "pqxx/internal/ignore-deprecated-pre.hxx"
90 return {tx, from_query, q};
91#include "pqxx/internal/ignore-deprecated-post.hxx"
92 }
93
104
106
122 static stream_from raw_table(
123 transaction_base &tx, std::string_view path,
124 std::string_view columns = ""sv);
125
127
129 static stream_from table(
131 std::initializer_list<std::string_view> columns = {});
133
135
137 [[deprecated("Use query() factory instead.")]] stream_from(
138 transaction_base &, from_query_t, std::string_view query);
139
141
143 [[deprecated("Use table() or raw_table() factory instead.")]] stream_from(
144 transaction_base &, from_table_t, std::string_view table);
145
147
149 template<typename Iter>
150 [[deprecated("Use table() or raw_table() factory instead.")]] stream_from(
151 transaction_base &, from_table_t, std::string_view table,
152 Iter columns_begin, Iter columns_end);
153
155
157 template<typename Columns>
158 [[deprecated("Use table() or raw_table() factory instead.")]] stream_from(
159 transaction_base &tx, from_table_t, std::string_view table,
160 Columns const &columns);
161
162#include "pqxx/internal/ignore-deprecated-pre.hxx"
164 [[deprecated("Use the from_table_t overload instead.")]] stream_from(
165 transaction_base &tx, std::string_view table) :
166 stream_from{tx, from_table, table}
167 {}
168#include "pqxx/internal/ignore-deprecated-post.hxx"
169
171 template<typename Columns>
172 [[deprecated("Use the from_table_t overload instead.")]] stream_from(
173 transaction_base &tx, std::string_view table, Columns const &columns) :
174 stream_from{tx, from_table, table, columns}
175 {}
176
178 template<typename Iter>
179 [[deprecated("Use the from_table_t overload instead.")]] stream_from(
180 transaction_base &, std::string_view table, Iter columns_begin,
181 Iter columns_end);
182
183 ~stream_from() noexcept;
184
186 [[nodiscard]] operator bool() const noexcept { return not m_finished; }
188 [[nodiscard]] bool operator!() const noexcept { return m_finished; }
189
191
197 void complete();
198
200
207 template<typename Tuple> stream_from &operator>>(Tuple &);
208
210 template<typename... Vs>
211 stream_from &operator>>(std::variant<Vs...> &) = delete;
212
214
218 template<typename... TYPE> [[nodiscard]] auto iter() &
219 {
220 return pqxx::internal::stream_input_iteration<TYPE...>{*this};
221 }
222
224
240 std::vector<zview> const *read_row() &;
241
243
244 raw_line get_raw_line();
245
246private:
247 // TODO: Clean up this signature once we cull the deprecated constructors.
250 transaction_base &tx, std::string_view table, std::string_view columns,
252
253 // TODO: Clean up this signature once we cull the deprecated constructors.
256 transaction_base &, std::string_view unquoted_table,
257 std::string_view columns, from_table_t, int);
258
259 template<typename Tuple, std::size_t... indexes>
260 void extract_fields(Tuple &t, std::index_sequence<indexes...>) const
261 {
262 (extract_value<Tuple, indexes>(t), ...);
263 }
264
265 pqxx::internal::glyph_scanner_func *m_glyph_scanner;
266
268 std::string m_row;
269
271 std::vector<zview> m_fields;
272
273 bool m_finished = false;
274
275 void close();
276
277 template<typename Tuple, std::size_t index>
278 void extract_value(Tuple &) const;
279
281 void parse_line();
282};
283
284
285template<typename Columns>
287 transaction_base &tx, from_table_t, std::string_view table_name,
288 Columns const &columns) :
290 tx, from_table, table_name, std::begin(columns), std::end(columns)}
291{}
292
293
294template<typename Iter>
296 transaction_base &tx, from_table_t, std::string_view table,
297 Iter columns_begin, Iter columns_end) :
299 tx, table, separated_list(",", columns_begin, columns_end),
300 from_table, 1}
301{}
302
303
304template<typename Tuple> inline stream_from &stream_from::operator>>(Tuple &t)
305{
306 if (m_finished)
307 return *this;
308 // C++20: constinit.
309 constexpr auto tup_size{std::tuple_size_v<Tuple>};
310 m_fields.reserve(tup_size);
311 parse_line();
312 if (m_finished)
313 return *this;
314
315 if (std::size(m_fields) != tup_size)
316 throw usage_error{internal::concat(
317 "Tried to extract ", tup_size, " field(s) from a stream of ",
318 std::size(m_fields), ".")};
319
320 extract_fields(t, std::make_index_sequence<tup_size>{});
321 return *this;
322}
323
324
325template<typename Tuple, std::size_t index>
326inline void stream_from::extract_value(Tuple &t) const
327{
328 using field_type = strip_t<decltype(std::get<index>(t))>;
329 using nullity = nullness<field_type>;
330 assert(index < std::size(m_fields));
331 if constexpr (nullity::always_null)
332 {
333 if (std::data(m_fields[index]) != nullptr)
334 throw conversion_error{"Streaming non-null value into null field."};
335 }
336 else if (std::data(m_fields[index]) == nullptr)
337 {
338 if constexpr (nullity::has_null)
339 std::get<index>(t) = nullity::null();
340 else
341 internal::throw_null_conversion(type_name<field_type>);
342 }
343 else
344 {
345 // Don't ever try to convert a non-null value to nullptr_t!
346 std::get<index>(t) = from_string<field_type>(m_fields[index]);
347 }
348}
349} // namespace pqxx
350#endif
The home of all libpqxx classes, functions, templates, etc.
Definition: array.hxx:23
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:39
std::remove_cv_t< std::remove_reference_t< TYPE > > strip_t
Remove any constness, volatile, and reference-ness from a type.
Definition: types.hxx:87
constexpr from_query_t from_query
Pass this to a stream_from constructor to stream query results.
Definition: stream_from.hxx:43
constexpr from_table_t from_table
Pass this to a stream_from constructor to stream table contents.
Definition: stream_from.hxx:38
std::initializer_list< std::string_view > table_path
Representation of a PostgreSQL table path.
Definition: connection.hxx:119
void PQXX_COLD throw_null_conversion(std::string const &type)
Definition: strconv.cxx:252
Error in usage of libpqxx library, similar to std::logic_error.
Definition: except.hxx:162
Value conversion failed, e.g. when converting "Hello" to int.
Definition: except.hxx:176
Traits describing a type's "null value," if any.
Definition: strconv.hxx:89
Stream data from the database.
Definition: stream_from.hxx:72
static stream_from query(transaction_base &tx, std::string_view q)
Factory: Execute query, and stream the results.
Definition: stream_from.hxx:87
std::pair< std::unique_ptr< char, std::function< void(char *)> >, std::size_t > raw_line
Definition: stream_from.hxx:75
stream_from & operator>>(std::variant< Vs... > &)=delete
Doing this with a std::variant is going to be horrifically borked.
stream_from(transaction_base &, from_query_t, std::string_view query)
Execute query, and stream over the results.
Definition: stream_from.cxx:37
stream_from & operator>>(Tuple &)
Read one row into a tuple.
Definition: stream_from.hxx:304
stream_from(transaction_base &tx, std::string_view table, Columns const &columns)
Definition: stream_from.hxx:172
stream_from(transaction_base &, std::string_view table, Iter columns_begin, Iter columns_end)
bool operator!() const noexcept
Has this stream produced all the data it is going to produce?
Definition: stream_from.hxx:188
stream_from(transaction_base &tx, std::string_view table)
Definition: stream_from.hxx:164
auto iter() &
Iterate over this stream. Supports range-based "for" loops.
Definition: stream_from.hxx:218
Interface definition (and common code) for "transaction" classes.
Definition: transaction_base.hxx:73
Base class for things that monopolise a transaction's attention.
Definition: transaction_focus.hxx:25
Marker for stream_from constructors: "stream from table.".
Definition: types.hxx:64
Marker for stream_from constructors: "stream from query.".
Definition: types.hxx:70