Qore Programming Language Reference Manual: Qore::ListHashIterator Class Reference (original) (raw)

This class an iterator class for lists of hashes as returned by Qore::SQL::Datasource::selectRows() and Qore::SQL::DatasourcePool::selectRows(), both of which return lists of columns where each list entry is a hash of the current column values. More...

#include <[QC_ListHashIterator.dox.h](%5Fq%5Fc%5F%5F%5Flist%5Fhash%5Fiterator%5F8dox%5F8h%5Fsource.html)>

This class an iterator class for lists of hashes as returned by Qore::SQL::Datasource::selectRows() and Qore::SQL::DatasourcePool::selectRows(), both of which return lists of columns where each list entry is a hash of the current column values.

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

Example: ListHashIterator basic usage

list data = (

{"column1": 1, "column2": "a"},

{"column1": 2, "column2": "b"},

);

ListHashIterator it(data);

while (it.next()) {

printf("iter %d: %n\n", it.index(), it.getValue());

}

iter 0: hash: (column1: 1, column2: "a")

iter 1: hash: (column1: 2, column2: "b")

Note

• In general, the ListHashIterator 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

ListHashReverseIterator

◆ constructor()

Creates the hash list iterator object.

Parameters

Example:

Note

the constructor's argument is softlist so that it can also accept NOTHING

◆ copy()

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

Example:

ListHashIterator ni = i.copy();

◆ empty()

◆ first()

◆ getKeyValue()

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

Code Flags:

RET_VALUE_ONLY

Parameters

Returns

the current column value of the given row

Example:

while (i.next()) {

printf("%d: value: %y", i.index(), i.getKeyValue("value"));

}

Exceptions

Note

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

◆ 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

Code Flags:

RET_VALUE_ONLY

Example:

while (i.next()) {

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

}

Note

equivalent to ListHashIterator::getValue()

Exceptions

◆ getValue()

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

Code Flags:

RET_VALUE_ONLY

Example:

while (i.next()) {

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

}

Note

• equivalent to ListHashIterator::getRow()

Exceptions

Implements Qore::AbstractIterator.

◆ 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()

◆ 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()

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

Returns

the current column value of the given row

Example:

while (i.next()) {

printf("%d: value: %y", i.index(), i.value);

}

Exceptions

Note

equivalent to ListHashIterator::getKeyValue() when called explicitly

◆ 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.

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

Implements Qore::AbstractIterator.

Reimplemented in Qore::ListHashReverseIterator.

◆ 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.

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

Implements Qore::AbstractBidirectionalIterator.

Reimplemented in Qore::ListHashReverseIterator.

◆ reset()

Reset the iterator instance to its initial state.

Reset the iterator instance to its initial state

Example

Exceptions

◆ set()

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

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

◆ valid()

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.