libpqxx  7.2.0
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) 2000-2020, 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 "pqxx/compiler-public.hxx"
17 #include "pqxx/internal/compiler-internal-pre.hxx"
18 
19 #include <cassert>
20 #include <functional>
21 #include <variant>
22 
23 #include "pqxx/except.hxx"
24 #include "pqxx/internal/encoding_group.hxx"
25 #include "pqxx/internal/stream_iterator.hxx"
26 #include "pqxx/internal/transaction_focus.hxx"
27 #include "pqxx/separated_list.hxx"
28 #include "pqxx/transaction_base.hxx"
29 
30 
31 namespace pqxx
32 {
37 
38 
40 
60 class PQXX_LIBEXPORT stream_from : internal::transactionfocus
61 {
62 public:
63  using raw_line =
64  std::pair<std::unique_ptr<char, std::function<void(char *)>>, std::size_t>;
65 
67 
76  stream_from(transaction_base &, from_query_t, std::string_view query);
77 
79 
82  stream_from(transaction_base &, from_table_t, std::string_view table);
83 
85 
88  template<typename Iter>
90  transaction_base &, from_table_t, std::string_view table,
91  Iter columns_begin, Iter columns_end);
92 
94 
97  template<typename Columns>
99  transaction_base &tx, from_table_t, std::string_view table,
100  Columns const &columns);
101 
103  stream_from(transaction_base &tx, std::string_view table) :
104  stream_from{tx, from_table, table}
105  {}
106 
108  template<typename Columns>
110  transaction_base &tx, std::string_view table, Columns const &columns) :
111  stream_from{tx, from_table, table, columns}
112  {}
113 
115  template<typename Iter>
116  stream_from(
117  transaction_base &, std::string_view table, Iter columns_begin,
118  Iter columns_end);
119 
120  ~stream_from() noexcept;
121 
122  [[nodiscard]] operator bool() const noexcept { return not m_finished; }
123  [[nodiscard]] bool operator!() const noexcept { return m_finished; }
124 
126 
132  void complete();
133 
135 
142  template<typename Tuple> stream_from &operator>>(Tuple &);
143 
145  template<typename... Vs>
146  stream_from &operator>>(std::variant<Vs...> &) = delete;
147 
149 
153  template<typename... TYPE>[[nodiscard]] auto iter()
154  {
155  return pqxx::internal::stream_input_iteration<TYPE...>{*this};
156  }
157 
159 
175  std::vector<zview> const *read_row();
176 
178 
179  raw_line get_raw_line();
180 
181 private:
182  stream_from(
183  transaction_base &tx, std::string_view table, std::string &&columns,
184  from_table_t);
185 
186  template<typename Tuple, std::size_t... indexes>
187  void extract_fields(Tuple &t, std::index_sequence<indexes...>) const
188  {
189  (extract_value<Tuple, indexes>(t), ...);
190  }
191 
192  static std::string compose_query(
193  transaction_base const &tx, std::string_view table,
194  std::string const &columns);
195 
196  pqxx::internal::glyph_scanner_func *m_glyph_scanner;
197 
199  std::string m_row;
200 
202  std::vector<zview> m_fields;
203 
204  bool m_finished = false;
205 
206  void close();
207 
208  template<typename Tuple, std::size_t index>
209  void extract_value(Tuple &) const;
210 
212  void parse_line();
213 };
214 
215 
216 template<typename Columns>
218  transaction_base &tb, from_table_t, std::string_view table_name,
219  Columns const &columns) :
220  stream_from{
221  tb, from_table, table_name, std::begin(columns), std::end(columns)}
222 {}
223 
224 
225 template<typename Iter>
227  transaction_base &tx, from_table_t, std::string_view table,
228  Iter columns_begin, Iter columns_end) :
229  stream_from{
230  tx, table, separated_list(",", columns_begin, columns_end),
231  from_table}
232 {}
233 
234 
235 template<typename Tuple> inline stream_from &stream_from::operator>>(Tuple &t)
236 {
237  if (m_finished)
238  return *this;
239  constexpr auto tup_size{std::tuple_size_v<Tuple>};
240  m_fields.reserve(tup_size);
241  parse_line();
242  if (m_finished)
243  return *this;
244 
245  if (std::size(m_fields) != tup_size)
246  throw usage_error{
247  "Tried to extract " + to_string(tup_size) +
248  " field(s) from a stream of " + to_string(std::size(m_fields)) + "."};
249 
250  extract_fields(t, std::make_index_sequence<tup_size>{});
251  return *this;
252 }
253 
254 
255 template<typename Tuple, std::size_t index>
256 inline void stream_from::extract_value(Tuple &t) const
257 {
258  using field_type = strip_t<decltype(std::get<index>(t))>;
259  using nullity = nullness<field_type>;
260  assert(index < std::size(m_fields));
261  if constexpr (nullity::always_null)
262  {
263  if (m_fields[index].data() != nullptr)
264  throw conversion_error{"Streaming non-null value into null field."};
265  }
266  else if (m_fields[index].data() == nullptr)
267  {
268  if constexpr (nullity::has_null)
269  std::get<index>(t) = nullity::null();
270  else
271  internal::throw_null_conversion(type_name<field_type>);
272  }
273  else
274  {
275  // Don't ever try to convert a non-null value to nullptr_t!
276  std::get<index>(t) = from_string<field_type>(m_fields[index]);
277  }
278 }
279 } // namespace pqxx
280 
281 #include "pqxx/internal/compiler-internal-post.hxx"
282 #endif
std::pair< std::unique_ptr< char, std::function< void(char *)> >, std::size_t > raw_line
Definition: stream_from.hxx:64
stream_from(transaction_base &tx, std::string_view table, Columns const &columns)
Definition: stream_from.hxx:109
auto iter()
Iterate over this stream. Supports range-based "for" loops.
Definition: stream_from.hxx:153
stream_from(transaction_base &tx, std::string_view table)
Definition: stream_from.hxx:103
Marker for stream_from constructors: "stream from query.".
Definition: types.hxx:59
std::string to_string(field const &value)
Convert a field to a string.
Definition: result.cxx:498
std::remove_cv_t< std::remove_reference_t< TYPE > > strip_t
Remove any constness, volatile, and reference-ness from a type.
Definition: util.hxx:120
The home of all libpqxx classes, functions, templates, etc.
Definition: array.hxx:25
Marker for stream_from constructors: "stream from table.".
Definition: types.hxx:55
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:40
Stream data from the database.
Definition: stream_from.hxx:60
constexpr from_query_t from_query
Pass this to a stream_from constructor to stream query results.
Definition: stream_from.hxx:36
stream_from(transaction_base &, from_query_t, std::string_view query)
Execute query, and stream over the results.
Definition: stream_from.cxx:56
Interface definition (and common code) for "transaction" classes.
Definition: transaction_base.hxx:67
Error in usage of libpqxx library, similar to std::logic_error.
Definition: except.hxx:164
void throw_null_conversion(std::string const &type)
Definition: strconv.cxx:243
constexpr from_table_t from_table
Pass this to a stream_from constructor to stream table contents.
Definition: stream_from.hxx:34
Value conversion failed, e.g. when converting "Hello" to int.
Definition: except.hxx:178
stream_from & operator>>(Tuple &)
Read one row into a tuple.
Definition: stream_from.hxx:235
Traits describing a type&#39;s "null value," if any.
Definition: strconv.hxx:86
bool operator!() const noexcept
Definition: stream_from.hxx:123