libpqxx  7.3.1
pqxx::cursor_base Class Reference

Common definitions for cursor types. More...

#include <cursor.hxx>

Public Types

enum  access_policy { forward_only, random_access }
 Cursor access-pattern policy. More...
 
enum  update_policy { read_only, update }
 Cursor update policy. More...
 
enum  ownership_policy { owned, loose }
 Cursor destruction policy. More...
 
using size_type = result_size_type
 
using difference_type = result_difference_type
 

Public Member Functions

 cursor_base ()=delete
 
 cursor_base (cursor_base const &)=delete
 
cursor_baseoperator= (cursor_base const &)=delete
 
std::string const & name () const noexcept
 Name of underlying SQL cursor. More...
 

Static Public Member Functions

Special movement distances.
static difference_type all () noexcept
 Special value: read until end. More...
 
static difference_type next () noexcept
 Special value: read one row only. More...
 
static difference_type prior () noexcept
 Special value: read backwards, one row only. More...
 
static difference_type backward_all () noexcept
 Special value: read backwards from current position back to origin. More...
 

Protected Member Functions

 cursor_base (connection &, std::string_view Name, bool embellish_name=true)
 

Protected Attributes

std::string const m_name
 

Detailed Description

Common definitions for cursor types.

In C++ terms, fetches are always done in pre-increment or pre-decrement fashion–i.e. the result does not include the row the cursor is on at the beginning of the fetch, and the cursor ends up being positioned on the last row in the result.

There are singular positions akin to end() at both the beginning and the end of the cursor's range of movement, although these fit in so naturally with the semantics that one rarely notices them. The cursor begins at the first of these, but any fetch in the forward direction will move the cursor off this position and onto the first row before returning anything.

Member Typedef Documentation

◆ difference_type

◆ size_type

Member Enumeration Documentation

◆ access_policy

Cursor access-pattern policy.

Allowing a cursor to move forward only can result in better performance, so use this access policy whenever possible.

Enumerator
forward_only 

Cursor can move forward only.

random_access 

Cursor can move back and forth.

◆ ownership_policy

Cursor destruction policy.

The normal thing to do is to make a cursor object the owner of the SQL cursor it represents. There may be cases, however, where a cursor needs to persist beyond the end of the current transaction (and thus also beyond the lifetime of the cursor object that created it!), where it can be "adopted" into a new cursor object. See the basic_cursor documentation for an explanation of cursor adoption.

If a cursor is created with "loose" ownership policy, the object representing the underlying SQL cursor will not take the latter with it when its own lifetime ends, nor will its originating transaction.

Warning
Use this feature with care and moderation. Only one cursor object should be responsible for any one underlying SQL cursor at any given time.
Enumerator
owned 

Destroy SQL cursor when cursor object is closed at end of transaction.

loose 

Leave SQL cursor in existence after close of object and transaction.

◆ update_policy

Cursor update policy.

Warning
Not all PostgreSQL versions support updatable cursors.
Enumerator
read_only 

Cursor can be used to read data but not to write.

update 

Cursor can be used to update data as well as read it.

Constructor & Destructor Documentation

◆ cursor_base() [1/3]

pqxx::cursor_base::cursor_base ( )
delete

◆ cursor_base() [2/3]

pqxx::cursor_base::cursor_base ( cursor_base const &  )
delete

◆ cursor_base() [3/3]

pqxx::cursor_base::cursor_base ( connection context,
std::string_view  Name,
bool  embellish_name = true 
)
protected

Member Function Documentation

◆ all()

pqxx::cursor_base::difference_type pqxx::cursor_base::all ( )
staticnoexcept

Special value: read until end.

Returns
Maximum value for result::difference_type, so the cursor will attempt to read the largest possible result set.

Implementation of libpqxx STL-style cursor classes.

These classes wrap SQL cursors in STL-like interfaces.

Copyright (c) 2000-2021, Jeroen T. Vermeulen.

See COPYING for copyright license. If you did not receive a file called COPYING with this source code, please notify the distributor of this mistake, or contact the author.

Referenced by cursor_base().

◆ backward_all()

pqxx::cursor_base::difference_type pqxx::cursor_base::backward_all ( )
staticnoexcept

Special value: read backwards from current position back to origin.

Returns
Minimum value for result::difference_type.

Referenced by pqxx::stateless_cursor< up, op >::stateless_cursor().

◆ name()

std::string const& pqxx::cursor_base::name ( ) const
noexcept

Name of underlying SQL cursor.

Returns
Name of SQL cursor, which may differ from original given name.
Warning
Don't use this to access the SQL cursor directly without going through the provided wrapper classes!

◆ next()

static difference_type pqxx::cursor_base::next ( )
staticnoexcept

Special value: read one row only.

Returns
Unsurprisingly, 1.

◆ operator=()

cursor_base& pqxx::cursor_base::operator= ( cursor_base const &  )
delete

◆ prior()

static difference_type pqxx::cursor_base::prior ( )
staticnoexcept

Special value: read backwards, one row only.

Returns
Unsurprisingly, -1.

Member Data Documentation

◆ m_name

std::string const pqxx::cursor_base::m_name
protected

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