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.
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| constructor (softlist< auto > l) |
| Creates the hash list iterator object. More...
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| copy () |
| Creates a copy of the ListHashIterator object, iterating the same object as the original and in the same position. More...
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bool | empty () |
| returns True if the result list is empty; False if not More...
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bool | first () |
| returns True if on the first element of the list More...
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auto | getKeyValue (string key) |
| Returns the current value for the column given as an argument. More...
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hash< auto > | getRow () |
| returns the current row value as a hash or throws an INVALID-ITERATOR exception if the iterator is invalid More...
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hash< auto > | getValue () |
| returns the current row value as a hash or throws an INVALID-ITERATOR exception if the iterator is invalid More...
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int | index () |
| returns the current iterator position in the list or -1 if not pointing at a valid element More...
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bool | last () |
| returns True if on the last element of the list More...
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int | max () |
| returns the number of elements in the list More...
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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...
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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...
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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...
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| reset () |
| Reset the iterator instance to its initial state. More...
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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...
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bool | valid () |
| returns True if the iterator is currently pointing at a valid element, False if not More...
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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<auto> 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")
string printf(string fmt,...)
Outputs the string passed to standard output, using the first argument as a format string; does not e...
- 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()
Qore::ListHashIterator::constructor |
( |
softlist< auto > |
l | ) |
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Creates the hash list iterator object.
- Parameters
-
l | the list of hashes to iterate |
- Example:
- Note
- the constructor's argument is softlist so that it can also accept NOTHING
◆ copy()
Qore::ListHashIterator::copy |
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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()
bool Qore::ListHashIterator::empty |
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virtual |
◆ first()
bool Qore::ListHashIterator::first |
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virtual |
◆ getKeyValue()
auto Qore::ListHashIterator::getKeyValue |
( |
string |
key | ) |
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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
- 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 or the list being iterated does not contain a hash element at the current iterator position or the given hash key does not exist |
- 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()
hash<auto> Qore::ListHashIterator::getRow |
( |
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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
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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 or the list being iterated does not contain a hash element at the current iterator position |
◆ getValue()
hash<auto> Qore::ListHashIterator::getValue |
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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
- Code Flags:
- RET_VALUE_ONLY
- Example:
while (i.next()) {
printf(
" + row %d: %y\n", i.index(), i.getValue());
}
- Note
-
- Exceptions
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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 or the list being iterated does not contain a hash element at the current iterator position |
Implements Qore::AbstractIterator.
◆ index()
int Qore::ListHashIterator::index |
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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::ListHashIterator::last |
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virtual |
◆ max()
int Qore::ListHashIterator::max |
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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::ListHashIterator::memberGate |
( |
string |
key | ) |
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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
- Example:
while (i.next()) {
printf(
"%d: value: %y", i.index(), i.value);
}
- Exceptions
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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 or the list being iterated does not contain a hash element at the current iterator position or the given hash key does not exist |
- Note
- equivalent to ListHashIterator::getKeyValue() when called explicitly
◆ next()
bool Qore::ListHashIterator::next |
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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::ListHashReverseIterator.
◆ prev()
bool Qore::ListHashIterator::prev |
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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::ListHashReverseIterator.
◆ reset()
Qore::ListHashIterator::reset |
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Reset the iterator instance to its initial state.
Reset the iterator instance to its initial state
- Example
- Exceptions
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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::ListHashIterator::set |
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int |
pos | ) |
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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);
string sprintf(string fmt,...)
Returns a formatted string based on a format string and other arguments; does not enforce field width...
- Exceptions
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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::ListHashIterator::valid |
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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.