Qore::HashListIterator Class Reference

This class an 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...

#include <QC_HashListIterator.dox.h>

Inheritance diagram for Qore::HashListIterator:

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 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...
bool	first ()
	returns True if on the first element of the list 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...
bool	last ()
	returns True if on the last element of the list 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...
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...
	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...
abstract bool	prev ()
	Moves the current position to the previous element; returns False if there are no more elements. More...
abstract auto	getValue ()
	returns the current value More...
abstract bool	next ()
	Moves the current position to the next element; returns False if there are no more elements. More...
abstract bool	valid ()
	returns True if the iterator is currently pointing at a valid element, False if not More...
abstract bool	empty ()
	returns True if the object to iterate is empty; False if not More...
abstract bool	first ()
	returns True if on the first element More...
abstract bool	last ()
	returns True if on the last element More...

Detailed Description

This class an 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.

This class can be used as a more flexible alternative to the context statement.

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

Example: HashListIterator basic usge

hash<auto> data = {
    "column1": (1, 2, 3,),
    "column2": ("a", "b", "c",),
    "column3": "constant",
};
 
HashListIterator 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: 1, column2: "a", column3: "constant"}; getKeyValue('column1'): 1
iter 1: getValue: {column1: 2, column2: "b", column3: "constant"}; getKeyValue('column1'): 2
iter 2: getValue: {column1: 3, column2: "c", column3: "constant"}; getKeyValue('column1'): 3

Note

• A hash with all non-list values will be iterated as if each key value were a single element list
• A hash with mixed lists and single values will have the single values used as the repeating value for every element in the list (as in the above example), however all lists must be of the same size or a runtime exception will be raised
• A hash with empty lists and constants will not be iterated; in this case the constant values will be ignored; values with lists determine the number of times the data structure will be iterated
• In general, the HashListIterator class is not designed to be accessed from multiple threads; it was created without locking for fast and efficient use when used from a single thread. For methods that would be unsafe to use in another thread, any use of such methods in threads other than the thread where the constructor was called will cause an ITERATOR-THREAD-ERROR to be thrown.

See also

HashListReverseIterator

Member Function Documentation

constructor() [1/2]

Qore::HashListIterator::constructor

(

)

Creates an empty hash list iterator object.

Example:

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

constructor() [2/2]

Qore::HashListIterator::constructor

(

hash< auto >

h

)

Creates the hash list iterator object.

Parameters

h	the hash of lists to iterate

Example:

HashListIterator i(h);

Note

a hash with non-list values will be iterated as if each key value were a single element list

copy()

Qore::HashListIterator::copy

(

)

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

Example:

HashListIterator ni = i.copy();

empty()

bool Qore::HashListIterator::empty ( )

virtual

returns True if the result list is empty; False if not

Returns

True if the result list is empty; False if not

Code Flags:

CONSTANT

Example:

if (i.empty())
    printf("the result list is empty\n");

Implements Qore::AbstractQuantifiedIterator.

first()

bool Qore::HashListIterator::first ( )

virtual

returns True if on the first element of the list

Returns

True if on the first element of the list

Code Flags:

CONSTANT

Example:

while (i.next()) {
    if (i.first())
        printf("START:\n");
}

Implements Qore::AbstractQuantifiedIterator.

Reimplemented in Qore::HashListReverseIterator.

getKeyValue()

auto Qore::HashListIterator::getKeyValue

(

string

key

)

Returns the current value for the column given as an argument.

Code Flags:

RET_VALUE_ONLY

Parameters

key	the 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.getKeyValue("value"));
}

Exceptions

ITERATOR-THREAD-ERROR	this exception is thrown if this method is called from any thread other than the thread that created the object
INVALID-ITERATOR	the iterator is not pointing at a valid element
HASHLISTITERATOR-ERROR	the hash key given has a value that is a list with a size that does not match the expected list size

Note

HashListIterator::memberGate() allows for the iterator to act as if it is a hash with members equal to the current row being iterated

getRow()

hash< auto > Qore::HashListIterator::getRow

(

)

returns the current row value as a hash or throws an INVALID-ITERATOR exception if the iterator is invalid

Returns

the current row value as a hash or throws an INVALID-ITERATOR exception if the iterator is invalid; each key value in the hash returned will be equal to the current list element for the element being iterated, or, if the key value in the hash being iterated is a constant (i.e. non-list) value, then this constant value will be returned as the key value directly

Code Flags:

RET_VALUE_ONLY

Example:

while (i.next()) {
    printf(" + row %d: %y\n", i.index(), i.getValue());
}

Note

equivalent to HashListIterator::getValue()

Exceptions

ITERATOR-THREAD-ERROR	this exception is thrown if this method is called from any thread other than the thread that created the object
INVALID-ITERATOR	the iterator is not pointing at a valid element
HASHLISTITERATOR-ERROR	the one of the hash keys has a value that is a list with a size that does not match the expected list size

getValue()

hash< auto > Qore::HashListIterator::getValue ( )

virtual

returns the current row value as a hash or throws an INVALID-ITERATOR exception if the iterator is invalid

Returns

the current row value as a hash or throws an INVALID-ITERATOR exception if the iterator is invalid; each key value in the hash returned will be equal to the current list element for the element being iterated, or, if the key value in the hash being iterated is a constant (i.e. non-list) value, then this constant value will be returned as the key value directly

Code Flags:

RET_VALUE_ONLY

Example:

while (i.next()) {
    printf(" + row %d: %y\n", i.index(), i.getValue());
}

Note

• equivalent to HashListIterator::getRow()

Exceptions

ITERATOR-THREAD-ERROR	this exception is thrown if this method is called from any thread other than the thread that created the object
INVALID-ITERATOR	the iterator is not pointing at a valid element
HASHLISTITERATOR-ERROR	the one of the hash keys has a value that is a list with a size that does not match the expected list size

Implements Qore::AbstractIterator.

index()

int Qore::HashListIterator::index

(

)

returns the current iterator position in the list or -1 if not pointing at a valid element

Returns

the current iterator position in the list or -1 if not pointing at a valid element

Code Flags:

CONSTANT

Example:

while (i.next()) {
    printf("+ %d/%d: %y\n", i.index(), i.max(), i.getValue());
}

last()

bool Qore::HashListIterator::last ( )

virtual

returns True if on the last element of the list

Returns

True if on the last element of the list

Code Flags:

CONSTANT

Example:

while (i.next()) {
    if (i.last())
        printf("END.\n");
}

Implements Qore::AbstractQuantifiedIterator.

Reimplemented in Qore::HashListReverseIterator.

max()

int Qore::HashListIterator::max

(

)

returns the number of elements in the list

Returns

the number of elements in the list

Code Flags:

CONSTANT

Example:

while (i.next()) {
    printf("+ %d/%d: %y\n", i.index(), i.max(), i.getValue());
}

memberGate()

auto Qore::HashListIterator::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

key	the 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-ERROR	this exception is thrown if this method is called from any thread other than the thread that created the object
INVALID-ITERATOR	the iterator is not pointing at a valid element
HASHLISTITERATOR-ERROR	the 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::HashListIterator::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-ERROR

this exception is thrown if this method is called from any thread other than the thread that created the object

Implements Qore::AbstractIterator.

Reimplemented in Qore::HashListReverseIterator.

prev()

bool Qore::HashListIterator::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-ERROR

this exception is thrown if this method is called from any thread other than the thread that created the object

Implements Qore::AbstractBidirectionalIterator.

Reimplemented in Qore::HashListReverseIterator.

reset()

Qore::HashListIterator::reset

(

)

Reset the iterator instance to its initial state.

Reset the iterator instance to its initial state

Example

i.reset();

Exceptions

ITERATOR-THREAD-ERROR

this exception is thrown if this method is called from any thread other than the thread that created the object

set()

bool Qore::HashListIterator::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

Parameters

pos	the new position for the iterator with 0 as the first element

Returns

False, meaning the iterator is not valid, otherwise it returns True

Example:

if (!i.set(pos))
    throw "INVALID-POSITION", sprintf("%d is an invalid position", pos);

Exceptions

ITERATOR-THREAD-ERROR

this exception is thrown if this method is called from any thread other than the thread that created the object

valid()

bool Qore::HashListIterator::valid ( )

virtual

returns True if the iterator is currently pointing at a valid element, False if not

Returns

True if the iterator is currently pointing at a valid element, False if not

Code Flags:

CONSTANT

Example:

if (i.valid())
    printf("current value: %y\n", i.getValue());

Implements Qore::AbstractIterator.