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[RFC] Iterator interface #103

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[RFC] Iterator interface #103

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d3a9db0
Stop returning l-Value references to temporaries
zauguin Mar 28, 2017
b4d3c0c
Added Iterator interface
zauguin Mar 28, 2017
6835def
Alternative interface
zauguin Mar 28, 2017
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87 changes: 84 additions & 3 deletions hdr/sqlite_modern_cpp.h
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Original file line number Diff line number Diff line change
Expand Up @@ -198,6 +198,57 @@ namespace sqlite {
}
bool used() const { return execution_started; }

template<class ...T>
class row_iterator {
public:
using difference_type = std::ptrdiff_t;
using value_type = std::tuple<T...>;
using pointer = const value_type*;;
using reference = const value_type&;
using iterator_category = std::input_iterator_tag;

row_iterator() = default;
explicit row_iterator(database_binder &binder): _binder(&binder) {
_binder->used(true);
++*this;
}

reference operator*() const { return _value; }
pointer operator->() const { return std::addressof(**this); }
row_iterator &operator++() {

switch(int result = sqlite3_step(_binder->_stmt.get())) {
case SQLITE_ROW:
tuple_iterate<value_type>::iterate(_value, *_binder);
break;
case SQLITE_DONE:
_binder = nullptr;
break;
default:
_binder = nullptr;
exceptions::throw_sqlite_error(result, _binder->sql());
}
return *this;
}

row_iterator operator++(int) const { auto old = *this; ++*this; return old; }
friend inline bool operator ==(const row_iterator &a, const row_iterator &b) {
return a._binder == b._binder;
}
friend inline bool operator !=(const row_iterator &a, const row_iterator &b) {
return !(a==b);
}

private:
database_binder *_binder = nullptr;
value_type _value;
};

template<class ...T>
inline auto as() &;
template<class ...T>
inline auto as() &&;

private:
std::shared_ptr<sqlite3> _db;
std::unique_ptr<sqlite3_stmt, decltype(&sqlite3_finalize)> _stmt;
Expand Down Expand Up @@ -372,6 +423,31 @@ namespace sqlite {
}
};

template<class ...T>
class owning_row_view
{
public:
owning_row_view(database_binder &&binder): _binder(std::move(binder)) {}
auto begin() { return database_binder::row_iterator<T...>(_binder); }
auto end() { return database_binder::row_iterator<T...>(); }
private:
database_binder _binder;
};
template<class ...T>
class row_view
{
public:
row_view(database_binder &binder): _binder(&binder) {}
auto begin() { return database_binder::row_iterator<T...>(*_binder); }
auto end() { return database_binder::row_iterator<T...>(); }
private:
database_binder *_binder;
};
template<class ...T>
auto database_binder::as() & { return row_view<T...>(*this); }
template<class ...T>
auto database_binder::as() && { return owning_row_view<T...>(std::move(*this)); }

namespace sql_function_binder {
template<
typename ContextType,
Expand Down Expand Up @@ -852,7 +928,7 @@ namespace sqlite {
#ifdef MODERN_SQLITE_STD_OPTIONAL_SUPPORT
template <typename OptionalT> inline database_binder& operator <<(database_binder& db, const std::optional<OptionalT>& val) {
if(val) {
return operator << (std::move(db), std::move(*val));
return operator << (db, std::move(*val));
}
int hresult;
if((hresult = sqlite3_bind_null(db._stmt.get(), db._inx)) != SQLITE_OK) {
Expand Down Expand Up @@ -893,7 +969,7 @@ namespace sqlite {
#ifdef _MODERN_SQLITE_BOOST_OPTIONAL_SUPPORT
template <typename BoostOptionalT> inline database_binder& operator <<(database_binder& db, const boost::optional<BoostOptionalT>& val) {
if(val) {
return operator << (std::move(db), std::move(*val));
return operator << (db, std::move(*val));
}
int hresult;
if((hresult = sqlite3_bind_null(db._stmt.get(), db._inx)) != SQLITE_OK) {
Expand Down Expand Up @@ -956,7 +1032,7 @@ namespace sqlite {
void inline operator++(database_binder& db, int) { db.execute(); db.reset(); }

// Convert the rValue binder to a reference and call first op<<, its needed for the call that creates the binder (be carefull of recursion here!)
template<typename T> database_binder& operator << (database_binder&& db, const T& val) { return db << val; }
template<typename T> database_binder&& operator << (database_binder&& db, const T& val) { db << val; return std::move(db); }

namespace sql_function_binder {
template<class T>
Expand Down Expand Up @@ -1098,4 +1174,9 @@ namespace sqlite {
}
}
}

template<class ...T>
auto as(database_binder &binder) { return row_view<T...>(binder); }
template<class ...T>
auto as(database_binder&&binder) { return owning_row_view<T...>(std::move(binder)); }
}
11 changes: 11 additions & 0 deletions tests/readme_example.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -49,6 +49,17 @@ int main() {
exit(EXIT_FAILURE);
cout << _age << ' ' << _name << ' ' << _weight << endl;
};
for(auto &&[_age, _name, _weight] : (db << "select age,name,weight from user where age > ? ;" << 21).as<int, string, double>()) {
if(_age != age || _name != name)
exit(EXIT_FAILURE);
cout << _age << ' ' << _name << ' ' << _weight << endl;
}

for(auto &&[_age, _name, _weight] : as<int, string, double>(db << "select age,name,weight from user where age > ? ;" << 21)) {
if(_age != age || _name != name)
exit(EXIT_FAILURE);
cout << _age << ' ' << _name << ' ' << _weight << endl;
}

// selects the count(*) from user table
// note that you can extract a single culumn single row result only to : int,long,long,float,double,string,u16string
Expand Down