QGIS API Documentation 3.27.0-Master (95e00c50d2)
qgsfeatureexpressionvaluesgatherer.h
Go to the documentation of this file.
1/***************************************************************************
2 qgsfeatureexpressionvaluesgatherer - QgsFeatureExpressionValuesGatherer
3 ---------------------
4 begin : 10.3.2017
5 copyright : (C) 2017 by Matthias Kuhn
7 ***************************************************************************
8 * *
9 * This program is free software; you can redistribute it and/or modify *
10 * it under the terms of the GNU General Public License as published by *
11 * the Free Software Foundation; either version 2 of the License, or *
12 * (at your option) any later version. *
13 * *
14 ***************************************************************************/
15#ifndef QGSFEATUREEXPRESSIONVALUESGATHERER_H
16#define QGSFEATUREEXPRESSIONVALUESGATHERER_H
17
18#include <QThread>
19#include <QMutex>
20#include "qgsapplication.h"
21#include "qgslogger.h"
22#include "qgsvectorlayer.h"
24
25#define SIP_NO_FILE
26
27// just internal guff - definitely not for exposing to public API!
29
36class QgsFeatureExpressionValuesGatherer: public QThread
37{
38 Q_OBJECT
39
40 public:
41
49 QgsFeatureExpressionValuesGatherer( QgsVectorLayer *layer,
50 const QString &displayExpression = QString(),
51 const QgsFeatureRequest &request = QgsFeatureRequest(),
52 const QStringList &identifierFields = QStringList() )
53 : mSource( new QgsVectorLayerFeatureSource( layer ) )
54 , mDisplayExpression( displayExpression.isEmpty() ? layer->displayExpression() : displayExpression )
55 , mRequest( request )
56 , mIdentifierFields( identifierFields )
57 {
58 }
59
60 struct Entry
61 {
62 Entry() = default;
63
64 Entry( const QVariantList &_identifierFields, const QString &_value, const QgsFeature &_feature )
65 : identifierFields( _identifierFields )
66 , featureId( _feature.isValid() ? _feature.id() : FID_NULL )
67 , value( _value )
68 , feature( _feature )
69 {}
70
71 Entry( const QgsFeatureId &_featureId, const QString &_value, const QgsVectorLayer *layer )
72 : featureId( _featureId )
73 , value( _value )
74 , feature( QgsFeature( layer ? layer->fields() : QgsFields() ) )
75 {}
76
77 QVariantList identifierFields;
78 QgsFeatureId featureId;
79 QString value;
80 QgsFeature feature;
81
82 bool operator()( const Entry &lhs, const Entry &rhs ) const;
83 };
84
85 static Entry nullEntry( QgsVectorLayer *layer )
86 {
87 return Entry( QVariantList(), QgsApplication::nullRepresentation(), QgsFeature( layer->fields() ) );
88 }
89
90 void run() override
91 {
92 mWasCanceled = false;
93
94 QgsFeatureIterator iterator = mSource->getFeatures( mRequest );
95
96 mDisplayExpression.prepare( &mExpressionContext );
97
98 QgsFeature feature;
99 QList<int> attributeIndexes;
100 for ( auto it = mIdentifierFields.constBegin(); it != mIdentifierFields.constEnd(); ++it )
101 attributeIndexes << mSource->fields().indexOf( *it );
102
103 while ( iterator.nextFeature( feature ) )
104 {
105 mExpressionContext.setFeature( feature );
106 QVariantList attributes;
107 for ( const int idx : attributeIndexes )
108 attributes << feature.attribute( idx );
109
110 const QString expressionValue = mDisplayExpression.evaluate( &mExpressionContext ).toString();
111
112 mEntries.append( Entry( attributes, expressionValue, feature ) );
113
114 const QMutexLocker locker( &mCancelMutex );
115 if ( mWasCanceled )
116 return;
117 }
118 }
119
121 void stop()
122 {
123 const QMutexLocker locker( &mCancelMutex );
124 mWasCanceled = true;
125 }
126
128 bool wasCanceled() const
129 {
130 const QMutexLocker locker( &mCancelMutex );
131 return mWasCanceled;
132 }
133
134 QVector<Entry> entries() const
135 {
136 return mEntries;
137 }
138
139 QgsFeatureRequest request() const
140 {
141 return mRequest;
142 }
143
147 QVariant data() const
148 {
149 return mData;
150 }
151
155 void setData( const QVariant &data )
156 {
157 mData = data;
158 }
159
160 protected:
161 QVector<Entry> mEntries;
162
163 private:
164 std::unique_ptr<QgsVectorLayerFeatureSource> mSource;
165 QgsExpression mDisplayExpression;
166 QgsExpressionContext mExpressionContext;
167 QgsFeatureRequest mRequest;
168 bool mWasCanceled = false;
169 mutable QMutex mCancelMutex;
170 QStringList mIdentifierFields;
171 QVariant mData;
172};
173
175
176
177#endif // QGSFEATUREEXPRESSIONVALUESGATHERER_H
static QString nullRepresentation()
This string is used to represent the value NULL throughout QGIS.
Expression contexts are used to encapsulate the parameters around which a QgsExpression should be eva...
Class for parsing and evaluation of expressions (formerly called "search strings").
Wrapper for iterator of features from vector data provider or vector layer.
bool nextFeature(QgsFeature &f)
This class wraps a request for features to a vector layer (or directly its vector data provider).
The feature class encapsulates a single feature including its unique ID, geometry and a list of field...
Definition: qgsfeature.h:56
bool isValid() const
Returns the validity of this feature.
Definition: qgsfeature.cpp:216
QVariant attribute(const QString &name) const
Lookup attribute value by attribute name.
Definition: qgsfeature.cpp:335
Q_GADGET QgsFeatureId id
Definition: qgsfeature.h:64
Container of fields for a vector layer.
Definition: qgsfields.h:45
Partial snapshot of vector layer's state (only the members necessary for access to features)
Represents a vector layer which manages a vector based data sets.
QgsFields fields() const FINAL
Returns the list of fields of this layer.
QString displayExpression
#define FID_NULL
Definition: qgsfeatureid.h:29
qint64 QgsFeatureId
64 bit feature ids negative numbers are used for uncommitted/newly added features
Definition: qgsfeatureid.h:28
const QgsAttributeList & attributeIndexes