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* This file is part of Soprano Project.
*
* Copyright (C) 2006 Daniele Galdi <daniele.galdi@gmail.com>
* Copyright (C) 2007-2009 Sebastian Trueg <trueg@kde.org>
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Library General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Library General Public License for more details.
*
* You should have received a copy of the GNU Library General Public License
* along with this library; see the file COPYING.LIB. If not, write to
* the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
* Boston, MA 02110-1301, USA.
*/
#ifndef SOPRANO_RESULT_SET_H
#define SOPRANO_RESULT_SET_H
#include "iterator.h"
#include "bindingset.h"
#include "statement.h"
#include "soprano_export.h"
#include <QtCore/QString>
#include <QtCore/QStringList>
namespace Soprano {
class Node;
class NodeIterator;
class QueryResultIteratorBackend;
class StatementIterator;
class BindingSet;
/**
* \class QueryResultIterator queryresultiterator.h Soprano/QueryResultIterator
*
* \brief 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:
*
* \li A Statement: Graph query results are represented as a stream of statements.
* See also currentStatement() and iterateStatements().
* \li A BindingSet: Tuple query results are represented by a set of variable bindings
* according to the variables used in the query. The bindings can be accessed as a set
* through the normal Iterator method current() or separately through #binding(int) const or
* #binding(const QString&) const.
* \li A boolean value: This is a special case in which the query was a boolean query
* (a SPARQL ASK query). In this case there is nothing to iterate but only a single
* boolean value which can be accessed through boolValue().
*
* <b>Example:</b>
*
* \code
* 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 ) );
* }
* \endcode
*
* 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:
*
* \code
* Soprano::QueryResultIterator it = model->executeQuery( someTupleQuery );
* QList<BindingSet> allBindings = it.allBindings();
* Q_FOREACH( Soprano::BindingSet bs, allBindings ) {
* modifyTheModel( model, bs );
* }
* \endcode
*
* Iterators have to be closed.
* This can either be achieved by deleting the iterator, finishing it (next() does return \p false),
* or calling close(). Before that other operations on the Model may block.
*
* Iterators are not thread-safe. Two threads using the same iterator may result
* in undefined behaviour and even crashes. An iterator needs to be closed by the
* same thread that opened it (except if the iterator contains special code to handle such
* a situation.)
*
* \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><br>Sebastian Trueg <trueg@kde.org>
*/
class SOPRANO_EXPORT QueryResultIterator : public Iterator<BindingSet>
{
public:
//@{
/**
* Creates and empty, invalid iterator.
*/
QueryResultIterator();
/**
* Copy constructor. Copies of iterators share their data.
*/
QueryResultIterator( const QueryResultIterator& );
/**
* Create a new QueryResultIterator which uses qr as backend.
* QueryResultIterator will take ownership of the QueryResultIteratorBackend.
*/
QueryResultIterator( QueryResultIteratorBackend *qr );
/**
* Destructor.
*/
virtual ~QueryResultIterator();
/**
* Copies of iterators share their data.
*/
QueryResultIterator& operator=( const QueryResultIterator& );
//@}
//@{
/**
* Retrieve the current Statement after a call to next.
* This method does only make sense for graph queries.
*/
Statement currentStatement() const;
/**
* Convenience method that puts all current bindings into one map.
* This method does only make sense for tuple queries.
*/
BindingSet currentBindings() const;
/**
* This method does only make sense for boolean queries.
*
* \return The result of a boolean query (SPARQL ASK).
*
* \sa isBool()
*/
bool boolValue() const;
//@}
//@{
/**
* Get the current binding for a variable by index.
*
* \param offset The index of the requested variable.
*
* This is equivalent to binding(int) const.
*
* \return The binding for the requested variable or and invalid
* node if offset is out of bounds, i.e. bigger or equal to bindingCount().
*
* \since 2.2
*/
Node operator[]( int offset ) const;
/**
* Get the current binding for a variable.
*
* \param name The name of the requested variable.
*
* This is equivalent to binding(const QString&) const.
*
* \return The binding for the requested variable or and invalid
* node if the bindings do not contain the variable.
*
* \since 2.2
*/
Node operator[]( const QString name ) const;
/**
* Get the current binding for a variable.
*
* \param name The name of the requested variable.
*
* This method does only make sense for tuple queries.
*
* \return The binding for the requested variable or and invalid
* node if the bindings do not contain the variable.
*/
Node binding( const QString &name ) const;
/**
* Get the current binding for a variable by index.
*
* \param offset The index of the requested variable.
*
* This method does only make sense for tuple queries.
*
* \return The binding for the requested variable or and invalid
* node if offset is out of bounds, i.e. bigger or equal to bindingCount().
*/
Node binding( int offset ) const;
/**
* The number of bindings in this query result.
*
* This method does only make sense for tuple queries.
*
* \return The number of bindings.
*/
int bindingCount() const;
/**
* This method does only make sense for tuple queries.
*
* \return The names of the bound variables in this query result.
*/
QStringList bindingNames() const;
//@}
//@{
/**
* Check if this is a graph result.
*
* \return \p true if this result refers to a graph query, i.e. currentStatement()
* and iterateStatements() return valid values.
*/
bool isGraph() const;
/**
* Check if this is a tuple result.
*
* \return \p true if this result refers to a tuple query, i.e. currentBindings(),
* binding(), bindingCount(), bindingNames(), and allBindings() return valid values.
*/
bool isBinding() const;
/**
* Check if this is a boolean result.
*
* There is no need to call next() for boolean results.
*
* \return \p true if this result refers to a boolean query (SPARQL ASK), i.e.
* boolValue() returns a valid value.
*/
bool isBool() const;
//@}
//@{
/**
* Convenience method that collects all binding sets that are left
* in the iterator.
*/
QList<BindingSet> allBindings();
/**
* 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.
*
* \return A wrapper iterator over the statements in a graph query.
*/
StatementIterator iterateStatements() 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.
*
* \param 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.
*
* \return A wrapper iterator over one column in a tuple query or an invalid iterator if the
* result does not contain bindings for variableName.
*/
NodeIterator 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.
*
* \param 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.
*
* \return 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().
*/
NodeIterator iterateBindings( int offset ) const;
/**
* Convenience method that creates an iterator over statements constructed from the values of the
* provided bindings.
*
* The typical usage would be with a query as follows:
*
* \code
* Soprano::StatementIterator it =
* model->executeQuery( "select * where { graph ?c { ?s ?p ?o . } }" )
* .iterateStatementsFromBindings( "s", "p", "o", "c" );
* \endcode
*
* \param subjectBindingName The name of the binding that will be used to set the subject of the
* constructed statements.
* \param predicateBindingName The name of the binding that will be used to set the predicate of the
* constructed statements.
* \param objectBindingName The name of the binding that will be used to set the object of the
* constructed statements.
* \param contextBindingName The name of the binding that will be used to set the context of the
* constructed statements.
* \param templateStatement If any of the provided binding names is empty the corresponding nodes
* in the resulting statements will be filled by templateStatement.
*
* \warning The new iterator is just a wrapper around this one. Thus, changing it will also
* change this one.
*
* \return A wrapper iterator over statements constructed from the specified bindings.
*
* \since 2.2
*/
StatementIterator iterateStatementsFromBindings( const QString& subjectBindingName,
const QString& predicateBindingName,
const QString& objectBindingName,
const QString& contextBindingName = QString(),
const Statement& templateStatement = Statement() ) const;
//@}
};
}
#endif // SOPRANO_RESULT_SET_H
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