Qore Programming Language Reference Manual  0.9.4.5
Qore::HashListReverseIterator Class Reference

This class a reverse iterator class for hashes of lists as returned by Qore::SQL::Datasource::select() and Qore::SQL::DatasourcePool::select(), both of which return hashes with keys giving column names where the key values are lists of column values. More...

Inheritance diagram for Qore::HashListReverseIterator:

Public Member Methods

 constructor (hash< auto > h)
 Creates the hash list iterator object. More...
 
 constructor ()
 Creates an empty hash list iterator object. More...
 
 copy ()
 Creates a copy of the HashListReverseIterator object, iterating the same object as the original and in the same position. More...
 
bool first ()
 returns True if on the first element being iterated in the list (ie the last element in the list) More...
 
bool last ()
 returns True if on the last element being iterated in the list (ie the first element in the list) More...
 
auto memberGate (string key)
 This method allows the iterator to be dereferenced directly as a hash for the current row being iterated, as memberGate methods are called implicitly when an unknown member is accessed from outside the class. More...
 
bool next ()
 Moves the current position to the next element in the result list; returns False if there are no more elements; if the iterator is not pointing at a valid element before this call, the iterator will be positioned on the first element in the list if the list is not empty. More...
 
bool prev ()
 Moves the current position to the previous element in the result list; returns False if there are no more elements; if the iterator is not pointing at a valid element before this call, the iterator will be positioned on the last element in the list if the list is not empty. More...
 
- Public Member Methods inherited from Qore::HashListIterator
 constructor (hash< auto > h)
 Creates the hash list iterator object. More...
 
 constructor ()
 Creates an empty hash list iterator object. More...
 
 copy ()
 Creates a copy of the HashListIterator object, iterating the same object as the original and in the same position. More...
 
bool empty ()
 returns True if the result list is empty; False if not More...
 
auto getKeyValue (string key)
 Returns the current value for the column given as an argument. More...
 
hash< auto > getRow ()
 returns the current row value as a hash or throws an INVALID-ITERATOR exception if the iterator is invalid More...
 
hash< auto > getValue ()
 returns the current row value as a hash or throws an INVALID-ITERATOR exception if the iterator is invalid More...
 
int index ()
 returns the current iterator position in the list or -1 if not pointing at a valid element More...
 
int max ()
 returns the number of elements in the list More...
 
auto memberGate (string key)
 This method allows the iterator to be dereferenced directly as a hash for the current row being iterated, as memberGate methods are called implicitly when an unknown member is accessed from outside the class. More...
 
 reset ()
 Reset the iterator instance to its initial state. More...
 
bool set (int pos)
 sets the new position in the result list; if the position is invalid then the method returns False, meaning the iterator is not valid, otherwise it returns True More...
 
bool valid ()
 returns True if the iterator is currently pointing at a valid element, False if not More...
 

Detailed Description

This class a reverse iterator class for hashes of lists as returned by Qore::SQL::Datasource::select() and Qore::SQL::DatasourcePool::select(), both of which return hashes with keys giving column names where the key values are lists of column values.

Like the Qore::HashListIterator class, this class can be used as a more flexible alternative to the context statement, except this class will iterate the result list in reverse order.

Call HashListReverseIterator::next() to iterate through the lists of column values assigned to each hash key in reverse order; do not use the iterator if HashListReverseIterator::next() returns False. A result list can be iterated in reverse order by calling HashListReverseIterator::prev() instead of HashListReverseIterator::next()

Example: HashListReverseIterator basic usge
hash<auto> data = {
"column1": (1, 2, 3,),
"column2": ("a", "b", "c",),
"column3": "constant",
};
HashListReverseIterator it(data);
while (it.next()) {
printf("iter %d: getValue: %y; getKeyValue('column1'): %y\n",
it.index(), it.getValue(), it.getKeyValue('column1'));
}
iter 0: getValue: {column1: 3, column2: "c", column3: "constant"}; getKeyValue('column1'): 3
iter 1: getValue: {column1: 2, column2: "b", column3: "constant"}; getKeyValue('column1'): 2
iter 2: getValue: {column1: 1, column2: "a", column3: "constant"}; getKeyValue('column1'): 1
Note
See also
HashListIterator

Member Function Documentation

◆ constructor() [1/2]

Qore::HashListReverseIterator::constructor ( hash< auto >  h)

Creates the hash list iterator object.

Parameters
hthe hash of lists to iterate
Example:
HashListReverseIterator i(h);

◆ constructor() [2/2]

Qore::HashListReverseIterator::constructor ( )

Creates an empty hash list iterator object.

Example:
*hash<auto> q = ds.select("select * from some_table");
HashListReverseIterator i(q);

◆ copy()

Qore::HashListReverseIterator::copy ( )

Creates a copy of the HashListReverseIterator object, iterating the same object as the original and in the same position.

Example:
HashListReverseIterator ni = i.copy();

◆ first()

bool Qore::HashListReverseIterator::first ( )
virtual

returns True if on the first element being iterated in the list (ie the last element in the list)

Returns
True if on the first element being iterated in the list (ie the last element in the list)
Code Flags:
CONSTANT
Example:
while (i.next()) {
if (i.first())
printf("START:\n");
}

Reimplemented from Qore::HashListIterator.

◆ last()

bool Qore::HashListReverseIterator::last ( )
virtual

returns True if on the last element being iterated in the list (ie the first element in the list)

Returns
True if on the last element being iterated in the list (ie the first element in the list)
Code Flags:
CONSTANT
Example:
while (i.next()) {
if (i.last())
printf("END.\n");
}

Reimplemented from Qore::HashListIterator.

◆ memberGate()

auto Qore::HashListReverseIterator::memberGate ( string  key)

This method allows the iterator to be dereferenced directly as a hash for the current row being iterated, as memberGate methods are called implicitly when an unknown member is accessed from outside the class.

Code Flags:
RET_VALUE_ONLY
Parameters
keythe column name for the value to retrieve
Returns
the current column value of the given row; the key value returned will be equal to the current list element for the given key, or, if the source key value is a constant (i.e. non-list) value, then this constant value will be returned directly
Example:
while (i.next()) {
printf("%d: value: %y", i.index(), i.value);
}
Exceptions
ITERATOR-THREAD-ERRORthis exception is thrown if this method is called from any thread other than the thread that created the object
INVALID-ITERATORthe iterator is not pointing at a valid element
HASHLISTITERATOR-ERRORthe hash key given has a value that is a list with a size that does not match the expected list size
Note
equivalent to HashListIterator::getKeyValue() when called explicitly

◆ next()

bool Qore::HashListReverseIterator::next ( )
virtual

Moves the current position to the next element in the result list; returns False if there are no more elements; if the iterator is not pointing at a valid element before this call, the iterator will be positioned on the first element in the list if the list is not empty.

This method will return True again after it returns False once if list is not empty, otherwise it will always return False. The iterator object should not be used after this method returns False

Returns
False if there are no more elements in the result list (in which case the iterator object is invalid and should not be used); True if successful (meaning that the iterator object is valid)
Example:
while (i.next()) {
printf(" + row %d: %y\n", i.index(), i.getValue());
}
Exceptions
ITERATOR-THREAD-ERRORthis exception is thrown if this method is called from any thread other than the thread that created the object

Reimplemented from Qore::HashListIterator.

◆ prev()

bool Qore::HashListReverseIterator::prev ( )
virtual

Moves the current position to the previous element in the result list; returns False if there are no more elements; if the iterator is not pointing at a valid element before this call, the iterator will be positioned on the last element in the list if the list is not empty.

This method will return True again after it returns False once if the list is not empty, otherwise it will always return False. The iterator object should not be used after this method returns False

Returns
False if there are no more elements in the result list (in which case the iterator object is invalid and should not be used); True if successful (meaning that the iterator object is valid)
Example:
while (i.prev()) {
printf(" + row %d: %y\n", i.index(), i.getValue());
}
Exceptions
ITERATOR-THREAD-ERRORthis exception is thrown if this method is called from any thread other than the thread that created the object

Reimplemented from Qore::HashListIterator.