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java.lang.Objectcom.trolltech.qt.internal.QSignalEmitterInternal
com.trolltech.qt.QSignalEmitter
com.trolltech.qt.QtJambiObject
com.trolltech.qt.xmlpatterns.QXmlQuery
public class QXmlQuery
The QXmlQuery class performs XQueries on XML data, or on non-XML data modeled to look like XML. The QXmlQuery class compiles and executes queries written in the 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 XML data model
as its delegate to the underlying query engine for traversing the data. The built-in data model is specified in XQuery 1.0 and XPath 2.0 Data Model.
QXmlQuery query = new QXmlQuery(); query.setQuery("doc('index.html')/html/body/p[1]"); QXmlSerializerPointer serializer(new QXmlSerializer(query, myOutputDevice)); query.evaluateToReceiver(serializer);The example uses QXmlQuery to match the first paragraph of an XML document and then
output the result
to a device as XML. Using QXmlQuery to query non-XML data requires writing a subclass of When Once a document has been parsed, its internal representation is maintained in the QXmlQuery instance and shared among multiple QXmlQuery instances. An instance 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
.Running Queries
To run a query set up with QXmlQuery, call one of the evaluation functions. QAbstractXmlReceiver
*) is called with a pointer to an XML 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.QXmlResultItems
*) is called with a pointer to an iterator for an empty sequence of query result items
. The Java-like iterator allows the query results to be accessed sequentially.QXmlResultItems
*), but the query must evaluate to a sequence of strings.Binding A Query To A Starting Node
When a query is run on XML data, as in the snippet above, the 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
.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.Error Handling
Errors can occur during query evaluation. Examples include type errors and file loading errors. When an error occurs: messageHandler()
.QXmlResultItems::hasError()
will return true, or evaluateTo()
will return false;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. 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. Â 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. QCoreApplication
must exist before QXmlQuery can be used.
Nested Class Summary |
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Nested classes/interfaces inherited from class com.trolltech.qt.QSignalEmitter |
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QSignalEmitter.AbstractSignal, QSignalEmitter.Signal0, QSignalEmitter.Signal1, QSignalEmitter.Signal2, QSignalEmitter.Signal3, QSignalEmitter.Signal4, QSignalEmitter.Signal5, QSignalEmitter.Signal6, QSignalEmitter.Signal7, QSignalEmitter.Signal8, QSignalEmitter.Signal9 |
Nested classes/interfaces inherited from class com.trolltech.qt.internal.QSignalEmitterInternal |
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com.trolltech.qt.internal.QSignalEmitterInternal.AbstractSignalInternal |
Field Summary |
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Fields inherited from class com.trolltech.qt.internal.QSignalEmitterInternal |
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currentSender |
Constructor Summary | |
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QXmlQuery()
Constructs an empty query. |
|
QXmlQuery(QXmlNamePool np)
Constructs a query that will use np as its name pool. |
|
QXmlQuery(QXmlQuery other)
Constructs a QXmlQuery that is a copy of other. |
Method Summary | |
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void |
bindVariable(QXmlName name,
QIODevice arg__2)
Binds the variable name to the device so that $name can be used from within the query to refer to the device. |
void |
bindVariable(QXmlName name,
QXmlItem value)
Binds the variable name to the value so that $name can be used from within the query to refer to the value. |
void |
bindVariable(java.lang.String localName,
QIODevice arg__2)
If localName is a valid NCName , this function is equivalent to the following snippet. |
void |
bindVariable(java.lang.String localName,
QXmlItem value)
This function constructs a QXmlName from localName using the query's namespace . |
void |
evaluateTo(QXmlResultItems result)
Starts the evaluation and makes it available in result. |
boolean |
isValid()
Returns true if this query is valid. |
QAbstractMessageHandler |
messageHandler()
Returns the message handler that handles compile and runtime messages for this QXmlQuery. |
QXmlNamePool |
namePool()
Returns the name pool used by this QXmlQuery for constructing names . |
QXmlQuery |
operator_assign(QXmlQuery other)
Assigns other to this QXmlQuery instance. |
void |
setFocus(QXmlItem item)
Sets the focus to item. |
void |
setMessageHandler(QAbstractMessageHandler messageHandler)
Changes the message handler for this QXmlQuery to aMessageHandler. |
void |
setQuery(QIODevice sourceCode)
Sets this QXmlQuery to an XQuery read from the sourceCode device. |
void |
setQuery(QIODevice sourceCode,
QUrl documentURI)
Sets this QXmlQuery to an XQuery read from the sourceCode device. |
void |
setQuery(QUrl queryURI)
Sets this QXmlQuery to the XQuery read from the queryURI. |
void |
setQuery(QUrl queryURI,
QUrl baseURI)
Sets this QXmlQuery to the XQuery read from the queryURI. |
void |
setQuery(java.lang.String sourceCode)
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. |
void |
setQuery(java.lang.String sourceCode,
QUrl documentURI)
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. |
void |
setUriResolver(QAbstractUriResolver resolver)
Sets the URI resolver to resolver. |
QAbstractUriResolver |
uriResolver()
Returns the query's URI resolver. |
Methods inherited from class com.trolltech.qt.QtJambiObject |
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dispose, disposed, equals, finalize, reassignNativeResources, tr, tr, tr |
Methods inherited from class com.trolltech.qt.QSignalEmitter |
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blockSignals, disconnect, disconnect, signalsBlocked, signalSender, thread |
Methods inherited from class com.trolltech.qt.internal.QSignalEmitterInternal |
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__qt_signalInitialization |
Methods inherited from class java.lang.Object |
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clone, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Methods inherited from interface com.trolltech.qt.QtJambiInterface |
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disableGarbageCollection, nativeId, nativePointer, reenableGarbageCollection, setJavaOwnership |
Constructor Detail |
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public QXmlQuery()
setQuery()
has been called.
public QXmlQuery(QXmlNamePool np)
setQuery()
has been called.
public QXmlQuery(QXmlQuery other)
Method Detail |
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public final void bindVariable(java.lang.String localName, QIODevice arg__2)
NCName
, this function is equivalent to the following snippet. query.bindVariable(new QXmlName(query.namePool(), localName), device);A
QXmlName
is constructed from localName, and is passed to the appropriate overload along with device. QXmlName::isNCName()
.
public final void bindVariable(java.lang.String localName, QXmlItem value)
QXmlName
from localName using the query's namespace
. The function then behaves as the overloaded function. It is equivalent to the following snippet. query.bindVariable(new QXmlName(query.namePool(), localName), value);
public final void bindVariable(QXmlName name, QIODevice arg__2)
QIODevice
device is exposed to the query as a URI of type xs:anyURI, which can be passed to the fn:doc() function to be read. E.g., this function can be used to pass an XML document in memory to fn:doc. QByteArray myDocument = new QByteArray(); QBuffer buffer = new QBuffer(myDocument); // This is a QIODevice. buffer.open(QIODevice.OpenModeFlag.ReadOnly); QXmlQuery query = new QXmlQuery(); query.bindVariable("myDocument", buffer); query.setQuery("declare variable $myDocument external; doc($myDocument)");The caller must ensure that device has been opened with at least
QIODevice::ReadOnly
prior to this binding. Otherwise, behavior is undefined. If the query will access an XML document contained in a QString, use a QBuffer
as shown in the following snippet. Suppose myQString contains <document>content</document>
The following code example is written in c++.
QBuffer device; device.setData(myQString.toUtf8()); device.open(QIODevice::ReadOnly)); QXmlQuery query; query.setQuery("declare variable $inputDocument external;" "doc($inputDocument)/query[theDocument]"); query.bindVariable("inputDocument", &device);name must not be null. name.isNull() must return false. If name has already been bound, its previous binding will be overriden. The URI that name evaluates to is arbitrary and may change.
If the type of the variable binding changes (e.g., if a previous binding by the same name was a QVariant
, or if there was no previous binding), isValid()
will return false, and recompilation of the query text is required. To recompile the query, call setQuery()
. For this reason, bindVariable()
should be called before setQuery()
, if possible.
Note:device must not be deleted while this QXmlQuery exists.
public final void bindVariable(QXmlName name, QXmlItem value)
name must not be null. name.isNull() must return false. If name has already been bound by a previous bindVariable()
call, its previous binding will be overriden.
If value is null so that value.isNull() returns true, and name already has a binding, the effect is to remove the existing binding for name.
To bind a value of type QString or QUrl
, wrap the value in a QVariant
such that QXmlItem
's QVariant
constructor is called.
All strings processed by the query must be valid XQuery strings, which means they must contain only XML 1.0 characters. However, this requirement is not checked. If the query processes an invalid string, the behavior is undefined.
QXmlItem::isNull()
.
public final void evaluateTo(QXmlResultItems result)
QXmlResultItems::next()
to get the enxt result. QXmlResultItems::next()
.
public final boolean isValid()
setQuery()
called for them yet.
public final QAbstractMessageHandler messageHandler()
setMessageHandler()
.
public final QXmlNamePool namePool()
names
. There is no setter for the name pool, because mixing name pools causes errors due to name confusion.
public final QXmlQuery operator_assign(QXmlQuery other)
public final void setFocus(QXmlItem item)
The focus can be accessed using the context item expression, i.e., dot (".").
By default, the focus is not set but is undefined. It will therefore result in a dynamic error, XPDY0002, if the query is evaluated without a focus. In fact, the focus must be set before the query is set with setQuery()
.
public final void setMessageHandler(QAbstractMessageHandler messageHandler)
message handler
for this QXmlQuery to aMessageHandler. The query sends all compile and runtime messages to this message handler. QXmlQuery does not take ownership of aMessageHandler. Normally, the default message handler is sufficient. It writes compile and runtime messages to stderr. The default message handler includes color codes if 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:
QtMsgType type | Only QtWarningMsg and QtFatalMsg are used. The former identifies a compile or runtime warning, while the latter identifies a dynamic or static error. |
const QString & description | An XHTML document which is the actual message. It is translated into the current language. |
const QUrl &identifier | Identifies the error with a URI, where the fragment is the error code, and the rest of the URI is the error namespace. |
const QSourceLocation & sourceLocation | Identifies where the error occurred. |
messageHandler()
.
public final void setQuery(QIODevice sourceCode)
QIODevice::ReadOnly
. documentURI represents the query obtained from the sourceCode device. It is the base URI of the static context, as defined in the XQuery language. It is used internally to resolve relative URIs that appear in the query, and for message reporting. documentURI can be empty. If it is empty, the 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 application file path
before it is used. If 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 false.
Variables must be bound before setQuery()
is called.
The encoding of the XQuery in sourceCode is detected internally using the rules for setting and detecting encoding of XQuery files, which are explained in the XQuery language.
isValid()
.
public final void setQuery(QIODevice sourceCode, QUrl documentURI)
QIODevice::ReadOnly
. documentURI represents the query obtained from the sourceCode device. It is the base URI of the static context, as defined in the XQuery language. It is used internally to resolve relative URIs that appear in the query, and for message reporting. documentURI can be empty. If it is empty, the 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 application file path
before it is used. If 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 false.
Variables must be bound before setQuery()
is called.
The encoding of the XQuery in sourceCode is detected internally using the rules for setting and detecting encoding of XQuery files, which are explained in the XQuery language.
isValid()
.
public final void setQuery(java.lang.String sourceCode)
QIODevice
*, const QUrl
&), after the XQuery has been read from the IO device into a string. Because sourceCode is already a Unicode string, detection of its encoding is unnecessary.
public final void setQuery(java.lang.String sourceCode, QUrl documentURI)
QIODevice
*, const QUrl
&), after the XQuery has been read from the IO device into a string. Because sourceCode is already a Unicode string, detection of its encoding is unnecessary.
public final void setQuery(QUrl queryURI)
isValid()
after calling this function. If an error occurred reading queryURI, e.g., the query does not exist, cannot be read, or is invalid, isValid()
will return false. The supported URI schemes are the same as those in the XQuery function fn:doc, except that queryURI can be the object of a variable binding.
baseURI is the Base URI of the static context, as defined in the XQuery language. It is used internally to resolve relative URIs that appear in the query, and for message reporting. If baseURI is empty, queryURI is used. Otherwise, baseURI is used, and it is resolved against the application file path
if it is relative.
If queryURI is empty or invalid, or if baseURI is invalid, the behavior of this function is undefined.
public final void setQuery(QUrl queryURI, QUrl baseURI)
isValid()
after calling this function. If an error occurred reading queryURI, e.g., the query does not exist, cannot be read, or is invalid, isValid()
will return false. The supported URI schemes are the same as those in the XQuery function fn:doc, except that queryURI can be the object of a variable binding.
baseURI is the Base URI of the static context, as defined in the XQuery language. It is used internally to resolve relative URIs that appear in the query, and for message reporting. If baseURI is empty, queryURI is used. Otherwise, baseURI is used, and it is resolved against the application file path
if it is relative.
If queryURI is empty or invalid, or if baseURI is invalid, the behavior of this function is undefined.
public final void setUriResolver(QAbstractUriResolver resolver)
uriResolver()
.
public final QAbstractUriResolver uriResolver()
The URI resolver provides a level of abstraction, or polymorphic URIs. A resolver can rewrite logical URIs to physical ones, or it can translate obsolete or invalid URIs to valid ones.
QtXmlPatterns calls the URI resolver for all URIs it encounters, except for namespaces. Specifically, all builtin functions that deal with URIs (fn:doc(), and fn:doc-available()).
In the case of fn:doc(), the absolute URI is the base URI in the static context (which most likely is the location of the query). Rather than use the URI the user specified, the return value of QAbstractUriResolver::resolve()
will be used.
When QtXmlPatterns calls QAbstractUriResolver::resolve()
the absolute URI is the URI mandated by the XQuery language, and the relative URI is the URI specified by the user.
setUriResolver()
.
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