libpqxx
The C++ client library for PostgreSQL
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result_iter.hxx
1
9#ifndef PQXX_H_RESULT_ITER
10#define PQXX_H_RESULT_ITER
11
12#include <memory>
13
14#include "pqxx/strconv.hxx"
15
16namespace pqxx
17{
18class result;
19} // namespace pqxx
20
21
22namespace pqxx::internal
23{
24// C++20: Replace with generator?
26template<typename... TYPE> class result_iter
27{
28public:
29 using value_type = std::tuple<TYPE...>;
30
32 result_iter() = default;
33
34 explicit result_iter(result const &home) :
35 m_home{&home}, m_size{std::size(home)}
36 {
37 if (not std::empty(home))
38 read();
39 }
40 result_iter(result_iter const &) = default;
41
42 result_iter &operator++()
43 {
44 m_index++;
45 if (m_index >= m_size)
46 m_home = nullptr;
47 else
48 read();
49 return *this;
50 }
51
53 bool operator==(result_iter const &rhs) const
54 {
55 return m_home == rhs.m_home;
56 }
57 bool operator!=(result_iter const &rhs) const { return not(*this == rhs); }
58
59 value_type const &operator*() const { return m_value; }
60
61private:
62 void read() { (*m_home)[m_index].convert(m_value); }
63
64 result const *m_home{nullptr};
65 result::size_type m_index{0};
66 result::size_type m_size;
67 value_type m_value;
68};
69
70
71template<typename... TYPE> class result_iteration
72{
73public:
74 using iterator = result_iter<TYPE...>;
75 explicit result_iteration(result const &home) : m_home{home}
76 {
77 constexpr auto tup_size{sizeof...(TYPE)};
78 if (home.columns() != tup_size)
80 "Tried to extract ", to_string(tup_size),
81 " field(s) from a result with ", to_string(home.columns()),
82 " column(s).")};
83 }
84 iterator begin() const
85 {
86 if (std::size(m_home) == 0)
87 return end();
88 else
89 return iterator{m_home};
90 }
91 iterator end() const { return {}; }
92
93private:
94 pqxx::result const m_home;
95};
96} // namespace pqxx::internal
97
98
99template<typename... TYPE> inline auto pqxx::result::iter() const
100{
101 return pqxx::internal::result_iteration<TYPE...>{*this};
102}
103
104
105template<typename CALLABLE>
107{
108 using args_tuple = internal::args_t<decltype(func)>;
109 constexpr auto sz{std::tuple_size_v<args_tuple>};
110 static_assert(
111 sz > 0,
112 "Callback for for_each must take parameters, one for each column in the "
113 "result.");
114
115 auto const cols{this->columns()};
116 if (sz != cols)
118 "Callback to for_each takes ", sz, "parameter", (sz == 1) ? "" : "s",
119 ", but result set has ", cols, "field", (cols == 1) ? "" : "s", ".")};
120
122 for (auto const r : *this) std::apply(func, r.as_tuple<pass_tuple>());
123}
124#endif
Reverse iterator for result. Use as result::const_reverse_iterator.
Definition result_iterator.hxx:194
Iterator for looped unpacking of a result.
Definition result_iter.hxx:27
result_iter()=default
Construct an "end" iterator.
bool operator==(result_iter const &rhs) const
Comparison only works for comparing to end().
Definition result_iter.hxx:53
Definition result_iter.hxx:72
Result set containing data returned by a query or command.
Definition result.hxx:73
PQXX_PURE row_size_type columns() const noexcept
Number of columns in result.
Definition result.cxx:493
void for_each(CALLABLE &&func) const
Run func on each row, passing the row's fields as parameters.
Definition result_iter.hxx:106
auto iter() const
Iterate rows, reading them directly into a tuple of "TYPE...".
Definition result_iter.hxx:99
Error in usage of libpqxx library, similar to std::logic_error.
Definition except.hxx:249
Internal items for libpqxx' own use. Do not use these yourself.
Definition encodings.cxx:33
std::string concat(TYPE... item)
Efficiently combine a bunch of items into one big string.
Definition concat.hxx:31
decltype(strip_types(std::declval< TYPES... >())) strip_types_t
Take a tuple type and apply strip_t to its component types.
Definition util.hxx:629
decltype(args_f(std::declval< CALLABLE >())) args_t
A callable's parameter types, as a tuple.
Definition util.hxx:616
The home of all libpqxx classes, functions, templates, etc.
Definition array.cxx:27
strip_t< decltype(*std::begin(std::declval< CONTAINER >()))> value_type
The type of a container's elements.
Definition types.hxx:94
PQXX_LIBEXPORT std::string to_string(field const &value)
Convert a field to a string.
Definition result.cxx:566