pqxx::result Class Reference

Result set containing data returned by a query or command. More...

Public Types
using	size_type = result_size_type
using	difference_type = result_difference_type
using	reference = row
using	const_iterator = const_result_iterator
using	pointer = const_iterator
using	iterator = const_iterator
using	const_reverse_iterator = const_reverse_result_iterator
using	reverse_iterator = const_reverse_iterator

Public Member Functions
	result (result const &rhs) noexcept=default
	result (result &&rhs) noexcept=default
result &	operator= (result const &rhs) noexcept=default
	Assign one result to another.
result &	operator= (result &&rhs) noexcept=default
	Assign one result to another, invaliding the old one.
Comparisons
You can compare results for equality. Beware: this is a very strict, dumb comparison. The smallest difference between two results (such as a string "Foo" versus a string "foo") will make them unequal.
bool	operator== (result const &) const noexcept
	Compare two results for equality.
bool	operator!= (result const &rhs) const noexcept
	Compare two results for inequality.
template<typename... TYPE>
auto	iter () const
	Iterate rows, reading them directly into a tuple of "TYPE...".
const_reverse_iterator	rbegin () const
const_reverse_iterator	crbegin () const
const_reverse_iterator	rend () const
const_reverse_iterator	crend () const
const_iterator	begin () const noexcept
const_iterator	cbegin () const noexcept
const_iterator	end () const noexcept
const_iterator	cend () const noexcept
reference	front () const noexcept
reference	back () const noexcept
PQXX_PURE size_type	size () const noexcept
PQXX_PURE bool	empty () const noexcept
size_type	capacity () const noexcept
void	swap (result &) noexcept
	Exchange two result values in an exception-safe manner.
row	operator[] (size_type i) const noexcept
	Index a row by number.
row	at (size_type) const
	Index a row by number, but check that the row number is valid.
field	at (size_type, row_size_type) const
	Index a field by row number and column number.
void	clear () noexcept
	Let go of the result's data.

Column information
class	pqxx::internal::gate::result_pipeline
class	pqxx::field
class	pqxx::internal::gate::result_creation
class	pqxx::internal::gate::result_connection
class	pqxx::internal::gate::result_row
class	pqxx::internal::gate::result_sql_cursor
PQXX_PURE row_size_type	columns () const noexcept
	Number of columns in result.
row_size_type	column_number (zview name) const
	Number of given column (throws exception if it doesn't exist).
char const *	column_name (row_size_type number) const &
	Name of column with this number (throws exception if it doesn't exist)
int	column_storage (row_size_type number) const
	Server-side storage size for field of column's type, in bytes.
int	column_type_modifier (row_size_type number) const noexcept
	Type modifier of the column with this number.
oid	column_type (row_size_type col_num) const
	Return column's type, as an OID from the system catalogue.
oid	column_type (zview col_name) const
	Return column's type, as an OID from the system catalogue.
oid	column_table (row_size_type col_num) const
	What table did this column come from?
oid	column_table (zview col_name) const
	What table did this column come from?
row_size_type	table_column (row_size_type col_num) const
	What column in its table did this column come from?
row_size_type	table_column (zview col_name) const
	What column in its table did this column come from?
PQXX_PURE std::string const &	query () const &noexcept
	Query that produced this result, if available (empty string otherwise)
PQXX_PURE oid	inserted_oid () const
	If command was an INSERT of 1 row, return oid of the inserted row.
PQXX_PURE size_type	affected_rows () const
	If command was INSERT, UPDATE, or DELETE: number of affected rows.
template<typename CALLABLE >
void	for_each (CALLABLE &&func) const
	Run func on each row, passing the row's fields as parameters.
result	expect_rows (size_type n) const
	Check that result contains exactly n rows.
row	one_row () const
	Check that result contains exactly 1 row, and return that row.
std::optional< row >	opt_row () const
	Expect that result contains at moost one row, and return as optional.
result	no_rows () const
	Expect that result contains no rows. Return result for convenience.
result	expect_columns (row_size_type cols) const
	Expect that result consists of exactly cols columns.
field	one_field () const
	Expect that result consists of exactly 1 row and 1 column.

Detailed Description

Result set containing data returned by a query or command.

This behaves as a container (as defined by the C++ standard library) and provides random access const iterators to iterate over its rows. You can also access a row by indexing a result R by the row's zero-based number:

for (result::size_type i=0; i < std::size(R); ++i) Process(R[i]);

Result sets in libpqxx are lightweight, reference-counted wrapper objects which are relatively small and cheap to copy. Think of a result object as a "smart pointer" to an underlying result set.

Warning

The result set that a result object points to is not thread-safe. If you copy a result object, it still refers to the same underlying result set. So never copy, destroy, query, or otherwise access a result while another thread may be copying, destroying, querying, or otherwise accessing the same result set–even if it is doing so through a different result object!

Member Function Documentation

affected_rows()

pqxx::result::size_type pqxx::result::affected_rows

(

)

const

If command was INSERT, UPDATE, or DELETE: number of affected rows.

Returns

Number of affected rows if last command was INSERT, UPDATE, or DELETE; zero for all other commands.

clear()

void pqxx::result::clear ( )

inlinenoexcept

Let go of the result's data.

Use this if you need to deallocate the result data earlier than you can destroy the result object itself.

Multiple result objects can refer to the same set of underlying data. The underlying data will be deallocated once all result objects that refer to it are cleared or destroyed.

column_storage()

int pqxx::result::column_storage

(

row_size_type

number

)

const

Server-side storage size for field of column's type, in bytes.

Returns the size of the server's internal representation of the column's data type. A negative value indicates the data type is variable-length.

column_type_modifier()

int pqxx::result::column_type_modifier ( row_size_type  number ) const

noexcept

Type modifier of the column with this number.

The meaning of modifier values is type-specific; they typically indicate precision or size limits.

Use this only if you know what you're doing. Most applications do not need it, and most types do not use modifiers.

The value -1 indicates "no information available."

Warning

There is no check for errors, such as an invalid column number.

expect_columns()

result pqxx::result::expect_columns ( row_size_type  cols ) const

inline

Expect that result consists of exactly cols columns.

Returns

The result itself, for convenience.

Exceptions

ref usage_error otherwise.

expect_rows()

result pqxx::result::expect_rows ( size_type  n ) const

inline

Check that result contains exactly n rows.

Returns

The result itself, for convenience.

Exceptions

ref unexpected_rows if the actual count is not equal to n.

for_each()

template<typename CALLABLE >

void pqxx::result::for_each ( CALLABLE &&  func ) const

inline

Run func on each row, passing the row's fields as parameters.

Goes through the rows from first to last. You provide a callable func.

For each row in the result, for_each will call func. It converts the row's fields to the types of func's parameters, and pass them to func.

(Therefore func must have a single signature. It can't be a generic lambda, or an object of a class with multiple overloaded function call operators. Otherwise, for_each will have no way to detect a parameter list without ambiguity.)

If any of your parameter types is std::string_view, it refers to the underlying storage of this result.

If any of your parameter types is a reference type, its argument will refer to a temporary value which only lives for the duration of that single invocation to func. If the reference is an lvalue reference, it must be const.

For example, this queries employee names and salaries from the database and prints how much each would like to earn instead:

tx.exec("SELECT name, salary FROM employee").for_each(
    [](std::string_view name, float salary){
        std::cout << name << " would like " << salary * 2 << ".\n";
    })

If func throws an exception, processing stops at that point and propagates the exception.

Exceptions

pqxx::usage_error

if func's number of parameters does not match the number of columns in this result.

The parameter types must have conversions from PostgreSQL's string format defined; see Supporting additional data types.

inserted_oid()

pqxx::oid pqxx::result::inserted_oid

(

)

const

If command was an INSERT of 1 row, return oid of the inserted row.

Returns

Identifier of inserted row if exactly one row was inserted, or oid_none otherwise.

iter()

template<typename... TYPE>

auto pqxx::result::iter ( ) const

inline

Iterate rows, reading them directly into a tuple of "TYPE...".

Converts the fields to values of the given respective types.

Use this only with a ranged "for" loop. The iteration produces std::tuple<TYPE...> which you can "unpack" to a series of auto variables.

one_field()

pqxx::field pqxx::result::one_field

(

)

const

Expect that result consists of exactly 1 row and 1 column.

Returns

The one pqxx::field in the result.

Exceptions

ref usage_error otherwise.

one_row()

pqxx::row pqxx::result::one_row

(

)

const

Check that result contains exactly 1 row, and return that row.

Returns

pqxx::row

Exceptions

ref unexpected_rows if the actual count is not equal to n.

operator=()

result & pqxx::result::operator= ( result const &  rhs )

defaultnoexcept

Assign one result to another.

Copying results is cheap: it copies only smart pointers, but the actual data stays in the same place.

operator[]()

pqxx::row pqxx::result::operator[] ( size_type  i ) const

noexcept

Index a row by number.

This returns a row object. Generally you should not keep the row around as a variable, but if you do, make sure that your variable is a row, not a row&.

opt_row()

std::optional< pqxx::row > pqxx::result::opt_row

(

)

const

Expect that result contains at moost one row, and return as optional.

Returns an empty std::optional if the result is empty, or if it has exactly one row, a std::optional containing the row.

Exceptions

ref unexpected_rows is the row count is not 0 or 1.

swap()

void pqxx::result::swap ( result &  rhs )

noexcept

Exchange two result values in an exception-safe manner.

If the swap fails, the two values will be exactly as they were before.

The swap is not necessarily thread-safe.

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The documentation for this class was generated from the following files:

• /home/docs/checkouts/readthedocs.org/user_builds/libpqxx/checkouts/stable/include/pqxx/result.hxx
• /home/docs/checkouts/readthedocs.org/user_builds/libpqxx/checkouts/stable/src/result.cxx
• /home/docs/checkouts/readthedocs.org/user_builds/libpqxx/checkouts/stable/include/pqxx/internal/result_iter.hxx
• /home/docs/checkouts/readthedocs.org/user_builds/libpqxx/checkouts/stable/include/pqxx/internal/result_iterator.hxx