[FEATURE][processing] New algorithm for extracting binary blobs from …

…fields Allows users to extract binary fields to files. The filename is set via a data defined expression, so can be taken from a column value or a more complex expression.
qgis · Nov 12, 2018 · e80c31e · e80c31e
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diff --git a/src/analysis/CMakeLists.txt b/src/analysis/CMakeLists.txt
@@ -41,6 +41,7 @@ SET(QGIS_ANALYSIS_SRCS
   processing/qgsalgorithmexplodehstore.cpp
   processing/qgsalgorithmextendlines.cpp
   processing/qgsalgorithmextenttolayer.cpp
+  processing/qgsalgorithmextractbinary.cpp
   processing/qgsalgorithmextractbyattribute.cpp
   processing/qgsalgorithmextractbyexpression.cpp
   processing/qgsalgorithmextractbyextent.cpp

diff --git a/src/analysis/processing/qgsalgorithmextractbinary.cpp b/src/analysis/processing/qgsalgorithmextractbinary.cpp
@@ -0,0 +1,156 @@
+/***************************************************************************
+                         qgsalgorithmextractbinary.cpp
+                         -----------------------------------
+    begin                : November 2018
+    copyright            : (C) 2018 by Nyall Dawson
+    email                : nyall dot dawson at gmail dot com
+ ***************************************************************************/
+
+/***************************************************************************
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU General Public License as published by  *
+ *   the Free Software Foundation; either version 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ ***************************************************************************/
+
+#include "qgsalgorithmextractbinary.h"
+#include "qgsfeaturerequest.h"
+
+///@cond PRIVATE
+
+QString QgsExtractBinaryFieldAlgorithm::name() const
+{
+  return QStringLiteral( "extractbinary" );
+}
+
+QString QgsExtractBinaryFieldAlgorithm::displayName() const
+{
+  return QObject::tr( "Extract binary field" );
+}
+
+QString QgsExtractBinaryFieldAlgorithm::shortHelpString() const
+{
+  return QObject::tr( "This algorithm extracts contents from a binary field, saving them to individual files." );
+}
+
+QString QgsExtractBinaryFieldAlgorithm::shortDescription() const
+{
+  return QObject::tr( "This algorithm extracts contents from a binary field, saving them to individual files." );
+}
+
+QStringList QgsExtractBinaryFieldAlgorithm::tags() const
+{
+  return QObject::tr( "blob,binaries,save,file,contents,field,column" ).split( ',' );
+}
+
+QString QgsExtractBinaryFieldAlgorithm::group() const
+{
+  return QObject::tr( "Vector table" );
+}
+
+QString QgsExtractBinaryFieldAlgorithm::groupId() const
+{
+  return QStringLiteral( "vectortable" );
+}
+
+QgsExtractBinaryFieldAlgorithm *QgsExtractBinaryFieldAlgorithm::createInstance() const
+{
+  return new QgsExtractBinaryFieldAlgorithm();
+}
+
+void QgsExtractBinaryFieldAlgorithm::initAlgorithm( const QVariantMap & )
+{
+  addParameter( new QgsProcessingParameterFeatureSource( QStringLiteral( "INPUT" ),
+                QObject::tr( "Input layer" ), QList< int>() << QgsProcessing::TypeVector ) );
+
+  addParameter( new QgsProcessingParameterField( QStringLiteral( "FIELD" ), QObject::tr( "Binary field" ), QVariant(),
+                QStringLiteral( "INPUT" ), QgsProcessingParameterField::Any ) );
+
+  std::unique_ptr< QgsProcessingParameterString > fileNameParam = qgis::make_unique< QgsProcessingParameterString >( QStringLiteral( "FILENAME" ), QObject::tr( "File name" ) );
+  fileNameParam->setIsDynamic( true );
+  fileNameParam->setDynamicPropertyDefinition( QgsPropertyDefinition( QStringLiteral( "Filename" ), QObject::tr( "File name" ), QgsPropertyDefinition::String ) );
+  fileNameParam->setDynamicLayerParameterName( QStringLiteral( "INPUT" ) );
+  addParameter( fileNameParam.release() );
+
+  addParameter( new QgsProcessingParameterFolderDestination( QStringLiteral( "FOLDER" ), QObject::tr( "Destination folder" ) ) );
+}
+
+QVariantMap QgsExtractBinaryFieldAlgorithm::processAlgorithm( const QVariantMap &parameters, QgsProcessingContext &context, QgsProcessingFeedback *feedback )
+{
+  std::unique_ptr< QgsProcessingFeatureSource > input( parameterAsSource( parameters, QStringLiteral( "INPUT" ), context ) );
+  if ( !input )
+    throw QgsProcessingException( invalidSourceError( parameters, QStringLiteral( "INPUT" ) ) );
+
+  QString fieldName = parameterAsString( parameters, QStringLiteral( "FIELD" ), context );
+  int fieldIndex = input->fields().lookupField( fieldName );
+  if ( fieldIndex < 0 )
+    throw QgsProcessingException( QObject::tr( "Invalid binary field" ) );
+
+  const QString folder = parameterAsString( parameters, QStringLiteral( "FOLDER" ), context );
+  if ( !QFileInfo::exists( folder ) )
+    throw QgsProcessingException( QObject::tr( "Destination folder %1 does not exist" ).arg( folder ) );
+
+  QDir dir( folder );
+  const QString filename = parameterAsString( parameters, QStringLiteral( "FILENAME" ), context );
+  bool dynamicFilename = QgsProcessingParameters::isDynamic( parameters, QStringLiteral( "FILENAME" ) );
+  QgsExpressionContext expressionContext = createExpressionContext( parameters, context, input.get() );
+  QgsProperty filenameProperty;
+
+  QSet< QString > fields;
+  fields.insert( fieldName );
+  QgsFeatureRequest request;
+  if ( dynamicFilename )
+  {
+    filenameProperty = parameters.value( QStringLiteral( "FILENAME" ) ).value< QgsProperty >();
+    filenameProperty.prepare( expressionContext );
+    fields.unite( filenameProperty.referencedFields() );
+  }
+  request.setSubsetOfAttributes( fields, input->fields() ).setFlags( QgsFeatureRequest::NoGeometry );
+  QgsFeatureIterator features = input->getFeatures( request, QgsProcessingFeatureSource::FlagSkipGeometryValidityChecks );
+  double step = input->featureCount() > 0 ? 100.0 / input->featureCount() : 1;
+  int i = 0;
+  QgsFeature feat;
+  while ( features.nextFeature( feat ) )
+  {
+    i++;
+    if ( feedback->isCanceled() )
+    {
+      break;
+    }
+
+    feedback->setProgress( i * step );
+
+    QByteArray ba = feat.attribute( fieldIndex ).toByteArray();
+    if ( ba.isEmpty() )
+      continue;
+
+    QString name = filename;
+    if ( dynamicFilename )
+    {
+      expressionContext.setFeature( feat );
+      name = filenameProperty.valueAsString( expressionContext, name );
+    }
+
+    const QString path = dir.filePath( name );
+    QFile file( path );
+    if ( !file.open( QIODevice::WriteOnly | QFile::Truncate ) )
+    {
+      feedback->reportError( QObject::tr( "Could not open %1 for writing" ).arg( path ) );
+    }
+    else
+    {
+      file.write( ba );
+      file.close();
+      feedback->pushInfo( QObject::tr( "Extracted %1" ).arg( path ) );
+    }
+  }
+
+  QVariantMap outputs;
+  outputs.insert( QStringLiteral( "FOLDER" ), folder );
+  return outputs;
+}
+
+
+///@endcond
diff --git a/src/analysis/processing/qgsalgorithmextractbinary.h b/src/analysis/processing/qgsalgorithmextractbinary.h
@@ -0,0 +1,58 @@
+/***************************************************************************
+                         qgsalgorithmextractbinary.h
+                         ---------------------------------
+    begin                : November 2018
+    copyright            : (C) 2018 by Nyall Dawson
+    email                : nyall dot dawson at gmail dot com
+ ***************************************************************************/
+
+/***************************************************************************
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU General Public License as published by  *
+ *   the Free Software Foundation; either version 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ ***************************************************************************/
+
+#ifndef QGSALGORITHMEXTRACTBINARY_H
+#define QGSALGORITHMEXTRACTBINARY_H
+
+#define SIP_NO_FILE
+
+#include "qgis.h"
+#include "qgsprocessingalgorithm.h"
+
+///@cond PRIVATE
+
+/**
+ * Native extract binary field algorithm.
+ */
+class QgsExtractBinaryFieldAlgorithm : public QgsProcessingAlgorithm
+{
+
+  public:
+
+    QgsExtractBinaryFieldAlgorithm() = default;
+    QString name() const override;
+    QString displayName() const override;
+    QStringList tags() const override;
+    QString group() const override;
+    QString groupId() const override;
+    QString shortHelpString() const override;
+    QString shortDescription() const override;
+    void initAlgorithm( const QVariantMap &configuration = QVariantMap() ) override;
+    QgsExtractBinaryFieldAlgorithm *createInstance() const override SIP_FACTORY;
+
+  protected:
+
+    QVariantMap processAlgorithm( const QVariantMap &parameters,
+                                  QgsProcessingContext &context, QgsProcessingFeedback *feedback ) override;
+
+};
+
+///@endcond PRIVATE
+
+#endif // QGSALGORITHMEXTRACTBINARY_H
+
+
diff --git a/src/analysis/processing/qgsnativealgorithms.cpp b/src/analysis/processing/qgsnativealgorithms.cpp
@@ -36,6 +36,7 @@
 #include "qgsalgorithmexplodehstore.h"
 #include "qgsalgorithmextendlines.h"
 #include "qgsalgorithmextenttolayer.h"
+#include "qgsalgorithmextractbinary.h"
 #include "qgsalgorithmextractbyattribute.h"
 #include "qgsalgorithmextractbyexpression.h"
 #include "qgsalgorithmextractbyextent.h"
@@ -163,6 +164,7 @@ void QgsNativeAlgorithms::loadAlgorithms()
   addAlgorithm( new QgsExplodeHstoreAlgorithm() );
   addAlgorithm( new QgsExtendLinesAlgorithm() );
   addAlgorithm( new QgsExtentToLayerAlgorithm() );
+  addAlgorithm( new QgsExtractBinaryFieldAlgorithm() );
   addAlgorithm( new QgsExtractByAttributeAlgorithm() );
   addAlgorithm( new QgsExtractByExpressionAlgorithm() );
   addAlgorithm( new QgsExtractByExtentAlgorithm() );