source: trunk/src/xmlpatterns/api/qxmlquery.cpp@ 745

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#include <QtCore/QBuffer>
#include <QtCore/QStringList>
#include <QtXmlPatterns/QXmlFormatter>

#include "qacceltreeresourceloader_p.h"
#include "qcommonvalues_p.h"
#include "qxmlresultitems.h"
#include "qxmlresultitems_p.h"
#include "qxmlserializer.h"
#include "qxpathhelper_p.h"

#include "qxmlquery.h"
#include "qxmlquery_p.h"

QT_BEGIN_NAMESPACE

/*!
  \class QXmlQuery

  \brief The QXmlQuery class performs XQueries on XML data, or on non-XML data modeled to look like XML.

  \reentrant
  \since 4.4
  \ingroup xml-tools

  The QXmlQuery class compiles and executes queries written in the
  \l {http://www.w3.org/TR/xquery/}{XQuery language}. QXmlQuery is
  typically used to query XML data, but it can also query non-XML
  data that has been modeled to look like XML.

  Using QXmlQuery to query XML data, as in the snippet below, is
  simple because it can use the built-in \l {QAbstractXmlNodeModel}
  {XML data model} as its delegate to the underlying query engine for
  traversing the data. The built-in data model is specified in \l
  {http://www.w3.org/TR/xpath-datamodel/} {XQuery 1.0 and XPath 2.0
  Data Model}.

  \snippet doc/src/snippets/code/src_xmlpatterns_api_qabstractxmlreceiver.cpp 0

  The example uses QXmlQuery to match the first paragraph of an XML
  document and then \l {QXmlSerializer} {output the result} to a
  device as XML.

  Using QXmlQuery to query \e {non-XML} data requires writing a
  subclass of QAbstractXmlNodeModel to use as a replacement for the
  built-in XML data model. The custom data model will be able to
  traverse the non-XML data as required by the QAbstractXmlNodeModel
  interface. An instance of this custom data model then becomes the
  delegate used by the query engine to traverse the non-XML data. For
  an example of how to use QXmlQuery to query non-XML data, see the
  documentation for QAbstractXmlNodeModel.

  \section1 Running XQueries

  To run a query set up with QXmlQuery, call one of the evaluation
  functions.

  \list

  \o evaluateTo(QAbstractXmlReceiver *) is called with a pointer to an
  XML \l {QAbstractXmlReceiver} {receiver}, which receives the query
  results as a sequence of callbacks. The receiver callback class is
  like the callback class used for translating the output of a SAX
  parser. QXmlSerializer, for example, is a receiver callback class
  for translating the sequence of callbacks for output as unformatted
  XML text.

  \endlist

  \list

  \o evaluateTo(QXmlResultItems *) is called with a pointer to an
  iterator for an empty sequence of query \l {QXmlResultItems} {result
  items}.  The Java-like iterator allows the query results to be
  accessed sequentially.

  \endlist

  \list

  \o evaluateTo(QStringList *) is like evaluateTo(QXmlResultItems *),
  but the query must evaluate to a sequence of strings.

  \endlist

  \section1 Running XPath Expressions

  The XPath language is a subset of the XQuery language, so
  running an XPath expression is the same as running an XQuery
  query. Pass the XPath expression to QXmlQuery using setQuery().

  \section1 Running XSLT stylesheets

  Running an XSLT stylesheet is like running an XQuery, except that
  when you construct your QXmlQuery, you must pass QXmlQuery::XSLT20
  to tell QXmlQuery to interpret whatever it gets from setQuery() as
  an XSLT stylesheet instead of as an XQuery. You must also set the
  input document by calling setFocus().

  \snippet doc/src/snippets/code/src_xmlpatterns_api_qxmlquery.cpp 7

  \note Currently, setFocus() must be called \e before setQuery() when
  using XSLT.

  Another way to run an XSLT stylesheet is to use the \c xmlpatterns
  command line utility.

  \code
  xmlpatterns myStylesheet.xsl myInput.xml
  \endcode

  \note For the current release, XSLT support should be considered
        experimental. See section \l{Using XML technologies#XSLT
        2.0}{XSLT conformance} for details.

  Stylesheet parameters are bound using bindVariable().

  \section1 Binding A Query To A Starting Node

  When a query is run on XML data, as in the snippet above, the
  \c{doc()} function returns the node in the built-in data model where
  the query evaluation will begin. But when a query is run on a custom
  node model containing non-XML data, one of the bindVariable()
  functions must be called to bind a variable name to a starting node
  in the custom model.  A $variable reference is used in the XQuery
  text to access the starting node in the custom model. It is not
  necessary to declare the variable name external in the query. See
  the example in the documentation for QAbstractXmlNodeModel.

  \section1 Reentrancy and Thread-Safety

  QXmlQuery is reentrant but not thread-safe. It is safe to use the
  QxmlQuery copy constructor to create a copy of a query and run the
  same query multiple times. Behind the scenes, QXmlQuery will reuse
  resources such as opened files and compiled queries to the extent
  possible. But it is not safe to use the same instance of QXmlQuery
  in multiple threads.

  \section1 Error Handling

  Errors can occur during query evaluation. Examples include type
  errors and file loading errors. When an error occurs:

  \list

  \o The error message is sent to the messageHandler().

  \o QXmlResultItems::hasError() will return \c{true}, or
  evaluateTo() will return \c{false};

  \o The results of the evaluation are undefined.

  \endlist

  \section1 Resource Management

  When a query runs, it parses documents, allocating internal data
  structures to hold them, and it may load other resources over the
  network. It reuses these allocated resources when possible, to
  avoid having to reload and reparse them.

  When setQuery() is called, the query text is compiled into an
  internal data structure and optimized. The optimized form can
  then be reused for multiple evaluations of the query. Since the
  compile-and-optimize process can be expensive, repeating it for
  the same query should be avoided by using a separate instance of
  QXmlQuery for each query text.

  Once a document has been parsed, its internal representation is
  maintained in the QXmlQuery instance and shared among multiple
  QXmlQuery instances.

  An instance of QCoreApplication must exist before QXmlQuery can be
  used.

  \section1 Event Handling

  When QXmlQuery accesses resources (e.g., calling \c fn:doc() to load a file,
  or accessing a device via a bound variable), the event loop is used, which
  means events will be processed. To avoid processing events when QXmlQuery
  accesses resources, create your QXmlQuery instance in a separate thread.
 */

/*!
 \enum QXmlQuery::QueryLanguage
 \since 4.5

 Specifies whether you want QXmlQuery to interpret the input to
 setQuery() as an XQuery or as an XSLT stylesheet.

 \value XQuery10 XQuery 1.0.
 \value XSLT20 XSLT 2.0
 \omitvalue XmlSchema11IdentityConstraintSelector The selector, the restricted
            XPath pattern found in W3C XML Schema 1.1 for uniqueness
            contraints. Apart from restricting the syntax, the type check stage
            for the expression assumes a sequence of nodes to be the focus.
 \omitvalue XmlSchema11IdentityConstraintField The field, the restricted
            XPath pattern found in W3C XML Schema 1.1 for uniqueness
            contraints. Apart from restricting the syntax, the type check stage
            for the expression assumes a sequence of nodes to be the focus.
 \omitvalue XPath20 Signifies XPath 2.0. Has no effect in the public API, it's
            used internally. As With XmlSchema11IdentityConstraintSelector and
            XmlSchema11IdentityConstraintField, the type check stage
            for the expression assumes a sequence of nodes to be the focus.

 \sa setQuery()
 */

// ### Qt5: Merge constructor overloads
/*!
  Constructs an invalid, empty query that cannot be used until
  setQuery() is called.

  \note This constructor must not be used if you intend to use
  this QXmlQuery to process XSL-T stylesheets. The other constructor
  must be used in that case.
 */
QXmlQuery::QXmlQuery() : d(new QXmlQueryPrivate())
{
}

/*!
  Constructs a QXmlQuery that is a copy of \a other. The new
  instance will share resources with the existing query
  to the extent possible.
 */
QXmlQuery::QXmlQuery(const QXmlQuery &other) : d(new QXmlQueryPrivate(*other.d))
{
    /* First we have invoked QXmlQueryPrivate's synthesized copy constructor.
     * Keep this section in sync with QXmlQuery::operator=(). */
    d->detach();
}

/*!
  Constructs a query that will use \a np as its name pool. The query
  cannot be evaluated until setQuery() has been called.
 */
QXmlQuery::QXmlQuery(const QXmlNamePool &np) : d(new QXmlQueryPrivate(np))
{
}

/*!

  Constructs a query that will be used to run Xqueries or XSL-T
  stylesheets, depending on the value of \a queryLanguage. It will use
  \a np as its name pool.

  \note If your QXmlQuery will process XSL-T stylesheets, this
  constructor must be used. The default constructor can only
  create instances of QXmlQuery for running XQueries.

  \note The XSL-T support in this release is considered experimental.
  See the \l{Using XML technologies#XSLT 2.0}{XSLT conformance} for
  details.

 \since 4.5
 \sa queryLanguage()
 */
QXmlQuery::QXmlQuery(QueryLanguage queryLanguage,
                     const QXmlNamePool &np) : d(new QXmlQueryPrivate(np))
{
    d->queryLanguage = queryLanguage;
}

/*!
  Destroys this QXmlQuery.
 */
QXmlQuery::~QXmlQuery()
{
    delete d;
}

/*!
  Assigns \a other to this QXmlQuery instance.
 */
QXmlQuery &QXmlQuery::operator=(const QXmlQuery &other)
{
    /* Keep this section in sync with QXmlQuery::QXmlQuery(const QXmlQuery &).
     */
    if(d != other.d)
    {
        *d = *other.d;
        d->detach();
    }

    return *this;
}

/*!
  Changes the \l {QAbstractMessageHandler}{message handler} for this
  QXmlQuery to \a aMessageHandler. The query sends all compile and
  runtime messages to this message handler. QXmlQuery does not take
  ownership of \a aMessageHandler.

  Normally, the default message handler is sufficient. It writes
  compile and runtime messages to \e stderr. The default message
  handler includes color codes if \e stderr can render colors.

  Note that changing the message handler after the query has been
  compiled has no effect, i.e. the query uses the same message handler
  at runtime that it uses at compile time.

  When QXmlQuery calls QAbstractMessageHandler::message(),
  the arguments are as follows:

  \table
  \header
    \o message() argument
    \o Semantics
  \row
    \o QtMsgType type
    \o Only QtWarningMsg and QtFatalMsg are used. The former
       identifies a compile or runtime warning, while the
       latter identifies a dynamic or static error.
  \row
    \o const QString & description
    \o An XHTML document which is the actual message. It is translated
       into the current language.
  \row
    \o const QUrl &identifier
    \o Identifies the error with a URI, where the fragment is
       the error code, and the rest of the URI is the error namespace.
  \row
    \o const QSourceLocation & sourceLocation
    \o Identifies where the error occurred.
  \endtable

 */
void QXmlQuery::setMessageHandler(QAbstractMessageHandler *aMessageHandler)
{
    d->messageHandler = aMessageHandler;
}

/*!
    Returns the message handler that handles compile and runtime
    messages for this QXmlQuery.
 */
QAbstractMessageHandler *QXmlQuery::messageHandler() const
{
    return d->messageHandler;
}

/*!
  Sets this QXmlQuery to an XQuery read from the \a sourceCode
  device.  The device must have been opened with at least
  QIODevice::ReadOnly.

  \a documentURI represents the query obtained from the \a sourceCode
  device. It is the base URI of the static context, as defined in the
  \l {http://www.w3.org/TR/xquery/}{XQuery language}. It is used
  internally to resolve relative URIs that appear in the query, and
  for message reporting. \a documentURI can be empty. If it is empty,
  the \l{QCoreApplication::applicationFilePath()} {application file
  path} is used. If it is not empty, it may be either relative or
  absolute. If it is relative, it is resolved itself against the
  \l {QCoreApplication::applicationFilePath()} {application file
  path} before it is used. If \a documentURI is neither a valid URI
  nor empty, the result is undefined.

  If the query contains a static error (e.g. syntax error), an error
  message is sent to the messageHandler(), and isValid() will return
  \e false.

  Variables must be bound before setQuery() is called.

  The encoding of the XQuery in \a sourceCode is detected internally
  using the rules for setting and detecting encoding of XQuery files,
  which are explained in the \l {http://www.w3.org/TR/xquery/}
  {XQuery language}.

  If \a sourceCode is \c null or not readable, or if \a documentURI is not
  a valid URI, behavior is undefined.
  \sa isValid()
 */
void QXmlQuery::setQuery(QIODevice *sourceCode, const QUrl &documentURI)
{
    if(!sourceCode)
    {
        qWarning("A null QIODevice pointer cannot be passed.");
        return;
    }

    if(!sourceCode->isReadable())
    {
        qWarning("The device must be readable.");
        return;
    }

    d->queryURI = QPatternist::XPathHelper::normalizeQueryURI(documentURI);
    d->expression(sourceCode);
}

/*!
  \overload
  The behavior and requirements of this function are the same as for
  setQuery(QIODevice*, const QUrl&), after the XQuery has been read
  from the IO device into a string. Because \a sourceCode is already
  a Unicode string, detection of its encoding is unnecessary.
*/
void QXmlQuery::setQuery(const QString &sourceCode, const QUrl &documentURI)
{
    Q_ASSERT_X(documentURI.isEmpty() || documentURI.isValid(), Q_FUNC_INFO,
               "The document URI must be valid.");

    QByteArray query(sourceCode.toUtf8());
    QBuffer buffer(&query);
    buffer.open(QIODevice::ReadOnly);

    setQuery(&buffer, documentURI);
}

/*!
  Sets this QXmlQuery to the XQuery read from the \a queryURI.  Use
  isValid() after calling this function. If an error occurred reading
  \a queryURI, e.g., the query does not exist, cannot be read, or is
  invalid, isValid() will return \e false.

  The supported URI schemes are the same as those in the XQuery
  function \c{fn:doc}, except that queryURI can be the object of
  a variable binding.

  \a baseURI is the Base URI of the static context, as defined in the
  \l {http://www.w3.org/TR/xquery/}{XQuery language}. It is used
  internally to resolve relative URIs that appear in the query, and
  for message reporting. If \a baseURI is empty, \a queryURI is used.
  Otherwise, \a baseURI is used, and it is resolved against the \l
  {QCoreApplication::applicationFilePath()} {application file path} if
  it is relative.

  If \a queryURI is empty or invalid, or if \a baseURI is invalid,
  the behavior of this function is undefined.