Soprano::QueryResultIterator Class Reference

An iterator for query results. More...

#include <Soprano/QueryResultIterator>

Inheritance diagram for Soprano::QueryResultIterator:

Inheritance graph
[legend]

List of all members.

Public Member Functions

 QueryResultIterator ()
 QueryResultIterator (const QueryResultIterator &)
 QueryResultIterator (QueryResultIteratorBackend *qr)
virtual ~QueryResultIterator ()
QueryResultIteratoroperator= (const QueryResultIterator &)
Statement currentStatement () const
BindingSet currentBindings () const
bool boolValue () const
Node binding (const QString &name) const
Node binding (int offset) const
int bindingCount () const
QStringList bindingNames () const
bool isGraph () const
bool isBinding () const
bool isBool () const
QList< BindingSetallBindings ()
StatementIterator iterateStatements () const
NodeIterator iterateBindings (const QString &variableName) const
NodeIterator iterateBindings (int offset) const


Detailed Description

An iterator for query results.

Query results in Soprano are wrapped in a QueryResultIterator.

Query iterators are returned by Model::executeQuery(). In contrast to NodeIterator or StatementIterator QueryResultIterator has a set of different access methods for the current dataset which can be one of three things:

Example:

 QueryResultIterator it = model->executeQuery( someGraphQuery );
 while( it.next() ) {
    doSomething( it.currentStatement() );
 }

 QueryResultIterator it2 = model->executeQuery( someTupleQuery );
 while( it.next() ) {
    doSomethingElse( it.currentBindings() );
    doSomethingCompletelyDifferent( it.binding( "x" ) );
    doSomethingEntirelyDifferent( it.binding( 0 ) );
 }

Many backends do lock the underlying Model during iteration. Thus, it is always a good idea to cache the results if they are to be used to modify the model to prevent a deadlock:

 Soprano::QueryResultIterator it = model->executeQuery( someTupleQuery );
 QList<BindingSet> allBindings = it.allBindings();
 Q_FOREACH( Soprano::BindingSet bs, allBindings ) {
    modifyTheModel( model, bs );
 }

Iterators have to be closed. This can either be achieved by deleting the iterator, finishing it (next() does return false), or calling close(). Before that other operations on the Model may block.

Iterators are not thread-safe. Two threads using the same iterator at the same time may result in undefined behaviour and even crashes.

Warning:
Be aware that iterators in Soprano are shared objects which means that copies of one iterator object work on the same data.
For further details on Soprano iterators see Iterator.

Author:
Daniele Galdi <daniele.galdi@gmail.com>
Sebastian Trueg <trueg@kde.org>

Definition at line 106 of file queryresultiterator.h.


Constructor & Destructor Documentation

Soprano::QueryResultIterator::QueryResultIterator (  ) 

Creates and empty, invalid iterator.

Soprano::QueryResultIterator::QueryResultIterator ( const QueryResultIterator  ) 

Copy constructor. Copies of iterators share their data.

Soprano::QueryResultIterator::QueryResultIterator ( QueryResultIteratorBackend qr  ) 

Create a new QueryResultIterator which uses qr as backend. QueryResultIterator will take ownership of the QueryResultIteratorBackend.

virtual Soprano::QueryResultIterator::~QueryResultIterator (  )  [virtual]

Destructor.


Member Function Documentation

QueryResultIterator& Soprano::QueryResultIterator::operator= ( const QueryResultIterator  ) 

Copies of iterators share their data.

Statement Soprano::QueryResultIterator::currentStatement (  )  const

Retrieve the current Statement after a call to next. This method does only make sense for graph queries.

BindingSet Soprano::QueryResultIterator::currentBindings (  )  const

Convenience method that puts all current bindings into one map. This method does only make sense for tuple queries.

bool Soprano::QueryResultIterator::boolValue (  )  const

This method does only make sense for boolean queries.

Returns:
The result of a boolean query (SPARQL ASK).
See also:
isBool()

Node Soprano::QueryResultIterator::binding ( const QString name  )  const

Get the current binding for a variable.

Parameters:
name The name of the requested variable.
This method does only make sense for tuple queries.

Returns:
The binding for the requested variable or and invalid node if the bindings do not contain the variable.

Node Soprano::QueryResultIterator::binding ( int  offset  )  const

Get the current binding for a variable by index.

Parameters:
offset The index of the requested variable.
This method does only make sense for tuple queries.

Returns:
The binding for the requested variable or and invalid node if offset is out of bounds, i.e. bigger or equal to bindingCount().

int Soprano::QueryResultIterator::bindingCount (  )  const

The number of bindings in this query result.

This method does only make sense for tuple queries.

Returns:
The number of bindings.

QStringList Soprano::QueryResultIterator::bindingNames (  )  const

This method does only make sense for tuple queries.

Returns:
The names of the bound variables in this query result.

bool Soprano::QueryResultIterator::isGraph (  )  const

Check if this is a graph result.

Returns:
true if this result refers to a graph query, i.e. currentStatement() and iterateStatements() return valid values.

bool Soprano::QueryResultIterator::isBinding (  )  const

Check if this is a tuple result.

Returns:
true if this result refers to a tuple query, i.e. currentBindings(), binding(), bindingCount(), bindingNames(), and allBindings() return valid values.

bool Soprano::QueryResultIterator::isBool (  )  const

Check if this is a boolean result.

There is no need to call next() for boolean results. However, for internal reasons backends need to always return true for boolean queries.

Returns:
true if this result refers to a boolean query (SPARQL ASK), i.e. boolValue() returns a valid value.

QList<BindingSet> Soprano::QueryResultIterator::allBindings (  ) 

Convenience method that collects all binding sets that are left in the iterator.

StatementIterator Soprano::QueryResultIterator::iterateStatements (  )  const

Convenience method that creates an iterator over the statements in this query result. This method does only make sense for graph queries.

Warning:
The new iterator is just a wrapper around this one. Thus, changing it will also change this one.
Returns:
A wrapper iterator over the statements in a graph query.

NodeIterator Soprano::QueryResultIterator::iterateBindings ( const QString variableName  )  const

Convenience method that creates an iterator over one column of bindings in this query result. This method does only make sense for tuple queries.

Parameters:
variableName The name of the requested variable.
Warning:
The new iterator is just a wrapper around this one. Thus, changing it will also change this one.
Returns:
A wrapper iterator over one column in a tuple query or an invalid iterator if the result does not contain bindings for variableName.

NodeIterator Soprano::QueryResultIterator::iterateBindings ( int  offset  )  const

Convenience method that creates an iterator over one column of bindings in this query result. This method does only make sense for tuple queries.

Parameters:
offset The index of the requested variable.
Warning:
The new iterator is just a wrapper around this one. Thus, changing it will also change this one.
Returns:
A wrapper iterator over one column in a tuple query or an invalid iterator if offset is out of bounds, i.e. bigger or equal to bindingCount().


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

Generated on Tue Jul 22 17:39:35 2008 for Soprano by  doxygen 1.5.6