QGIS API Documentation 3.34.0-Prizren (ffbdd678812)
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qgsfeaturesource.cpp
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1/***************************************************************************
2 qgsfeaturesource.cpp
3 -------------------
4 begin : May 2017
5 copyright : (C) 2017 by Nyall Dawson
6 email : nyall dot dawson at gmail dot com
7 ***************************************************************************/
8
9/***************************************************************************
10 * *
11 * This program is free software; you can redistribute it and/or modify *
12 * it under the terms of the GNU General Public License as published by *
13 * the Free Software Foundation; either version 2 of the License, or *
14 * (at your option) any later version. *
15 * *
16 ***************************************************************************/
17
18#include "qgsfeaturesource.h"
19#include "qgsfeaturerequest.h"
20#include "qgsfeatureiterator.h"
22#include "qgsfeedback.h"
23#include "qgsvectorlayer.h"
25
30
31QSet<QVariant> QgsFeatureSource::uniqueValues( int fieldIndex, int limit ) const
32{
33 if ( fieldIndex < 0 || fieldIndex >= fields().count() )
34 return QSet<QVariant>();
35
38 req.setSubsetOfAttributes( QgsAttributeList() << fieldIndex );
39
40 QSet<QVariant> values;
42 QgsFeature f;
43 while ( it.nextFeature( f ) )
44 {
45 values.insert( f.attribute( fieldIndex ) );
46 if ( limit > 0 && values.size() >= limit )
47 return values;
48 }
49 return values;
50}
51
52QVariant QgsFeatureSource::minimumValue( int fieldIndex ) const
53{
54 if ( fieldIndex < 0 || fieldIndex >= fields().count() )
55 return QVariant();
56
59 req.setSubsetOfAttributes( QgsAttributeList() << fieldIndex );
60
61 QVariant min;
63 QgsFeature f;
64 while ( it.nextFeature( f ) )
65 {
66 const QVariant v = f.attribute( fieldIndex );
67 if ( !QgsVariantUtils::isNull( v ) && ( qgsVariantLessThan( v, min ) || QgsVariantUtils::isNull( min ) ) )
68 {
69 min = v;
70 }
71 }
72 return min;
73}
74
75QVariant QgsFeatureSource::maximumValue( int fieldIndex ) const
76{
77 if ( fieldIndex < 0 || fieldIndex >= fields().count() )
78 return QVariant();
79
82 req.setSubsetOfAttributes( QgsAttributeList() << fieldIndex );
83
84 QVariant max;
86 QgsFeature f;
87 while ( it.nextFeature( f ) )
88 {
89 const QVariant v = f.attribute( fieldIndex );
90 if ( !QgsVariantUtils::isNull( v ) && ( qgsVariantGreaterThan( v, max ) || QgsVariantUtils::isNull( max ) ) )
91 {
92 max = v;
93 }
94 }
95 return max;
96}
97
99{
100 QgsRectangle r;
101
103 req.setNoAttributes();
104
106 QgsFeature f;
107 while ( it.nextFeature( f ) )
108 {
109 if ( f.hasGeometry() )
111 }
112 return r;
113}
114
116{
119 .setNoAttributes() );
120
121 QgsFeatureIds ids;
122
123 QgsFeature fet;
124 while ( fit.nextFeature( fet ) )
125 {
126 ids << fet.id();
127 }
128
129 return ids;
130}
131
133{
136
137 const QgsAttributeList requestedAttrs = request.subsetOfAttributes();
138
139 QgsFields outFields;
141 {
142 int i = 0;
143 const QgsFields sourceFields = fields();
144 for ( const QgsField &field : sourceFields )
145 {
146 if ( requestedAttrs.contains( i ) )
147 outFields.append( field );
148 i++;
149 }
150 }
151 else
152 {
153 outFields = fields();
154 }
155
156 std::unique_ptr< QgsVectorLayer > layer( QgsMemoryProviderUtils::createMemoryLayer(
157 sourceName(),
158 outFields,
159 outWkbType,
160 crs ) );
161 QgsFeature f;
162 QgsFeatureIterator it = getFeatures( request );
163 const int fieldCount = fields().count();
164 while ( it.nextFeature( f ) )
165 {
166 if ( feedback && feedback->isCanceled() )
167 break;
168
170 {
171 // remove unused attributes
172 QgsAttributes attrs;
173 for ( int i = 0; i < fieldCount; ++i )
174 {
175 if ( requestedAttrs.contains( i ) )
176 {
177 attrs.append( f.attributes().at( i ) );
178 }
179 }
180
181 f.setAttributes( attrs );
182 }
183
184 layer->dataProvider()->addFeature( f, QgsFeatureSink::FastInsert );
185 }
186
187 return layer.release();
188}
189
194
WkbType
The WKB type describes the number of dimensions a geometry has.
Definition qgis.h:182
@ NoGeometry
No geometry.
A vector of attributes.
This class represents a coordinate reference system (CRS).
bool isValid() const
Returns whether this CRS is correctly initialized and usable.
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).
QgsFeatureRequest & setFlags(QgsFeatureRequest::Flags flags)
Sets flags that affect how features will be fetched.
Flags flags() const
Returns the flags which affect how features are fetched.
QgsFeatureRequest & setSubsetOfAttributes(const QgsAttributeList &attrs)
Set a subset of attributes that will be fetched.
QgsCoordinateReferenceSystem destinationCrs() const
Returns the destination coordinate reference system for feature's geometries, or an invalid QgsCoordi...
@ SubsetOfAttributes
Fetch only a subset of attributes (setSubsetOfAttributes sets this flag)
@ NoGeometry
Geometry is not required. It may still be returned if e.g. required for a filter condition.
QgsFeatureRequest & setNoAttributes()
Set that no attributes will be fetched.
QgsAttributeList subsetOfAttributes() const
Returns the subset of attributes which at least need to be fetched.
@ FastInsert
Use faster inserts, at the cost of updating the passed features to reflect changes made at the provid...
virtual QgsFields fields() const =0
Returns the fields associated with features in the source.
virtual QSet< QVariant > uniqueValues(int fieldIndex, int limit=-1) const
Returns the set of unique values contained within the specified fieldIndex from this source.
virtual QgsCoordinateReferenceSystem sourceCrs() const =0
Returns the coordinate reference system for features in the source.
SpatialIndexPresence
Enumeration of spatial index presence states.
@ SpatialIndexUnknown
Spatial index presence cannot be determined, index may or may not exist.
virtual Qgis::WkbType wkbType() const =0
Returns the geometry type for features returned by this source.
virtual FeatureAvailability hasFeatures() const
Determines if there are any features available in the source.
FeatureAvailability
Possible return value for hasFeatures() to determine if a source is empty.
@ FeaturesMaybeAvailable
There may be features available in this source.
virtual QVariant minimumValue(int fieldIndex) const
Returns the minimum value for an attribute column or an invalid variant in case of error.
virtual QgsFeatureIterator getFeatures(const QgsFeatureRequest &request=QgsFeatureRequest()) const =0
Returns an iterator for the features in the source.
QgsVectorLayer * materialize(const QgsFeatureRequest &request, QgsFeedback *feedback=nullptr)
Materializes a request (query) made against this feature source, by running it over the source and re...
virtual QString sourceName() const =0
Returns a friendly display name for the source.
virtual QVariant maximumValue(int fieldIndex) const
Returns the maximum value for an attribute column or an invalid variant in case of error.
virtual QgsFeatureIds allFeatureIds() const
Returns a list of all feature IDs for features present in the source.
virtual SpatialIndexPresence hasSpatialIndex() const
Returns an enum value representing the presence of a valid spatial index on the source,...
virtual QgsRectangle sourceExtent() const
Returns the extent of all geometries from the source.
The feature class encapsulates a single feature including its unique ID, geometry and a list of field...
Definition qgsfeature.h:56
QgsAttributes attributes
Definition qgsfeature.h:65
QgsFeatureId id
Definition qgsfeature.h:64
void setAttributes(const QgsAttributes &attrs)
Sets the feature's attributes.
QgsGeometry geometry
Definition qgsfeature.h:67
bool hasGeometry() const
Returns true if the feature has an associated geometry.
QVariant attribute(const QString &name) const
Lookup attribute value by attribute name.
Base class for feedback objects to be used for cancellation of something running in a worker thread.
Definition qgsfeedback.h:45
bool isCanceled() const
Tells whether the operation has been canceled already.
Definition qgsfeedback.h:54
Encapsulate a field in an attribute table or data source.
Definition qgsfield.h:53
Container of fields for a vector layer.
Definition qgsfields.h:45
bool append(const QgsField &field, FieldOrigin origin=OriginProvider, int originIndex=-1)
Appends a field. The field must have unique name, otherwise it is rejected (returns false)
Definition qgsfields.cpp:59
int count() const
Returns number of items.
QgsRectangle boundingBox() const
Returns the bounding box of the geometry.
static QgsVectorLayer * createMemoryLayer(const QString &name, const QgsFields &fields, Qgis::WkbType geometryType=Qgis::WkbType::NoGeometry, const QgsCoordinateReferenceSystem &crs=QgsCoordinateReferenceSystem(), bool loadDefaultStyle=true) SIP_FACTORY
Creates a new memory layer using the specified parameters.
A rectangle specified with double values.
void combineExtentWith(const QgsRectangle &rect)
Expands the rectangle so that it covers both the original rectangle and the given rectangle.
static bool isNull(const QVariant &variant)
Returns true if the specified variant should be considered a NULL value.
Represents a vector layer which manages a vector based data sets.
bool qgsVariantLessThan(const QVariant &lhs, const QVariant &rhs)
Compares two QVariant values and returns whether the first is less than the second.
Definition qgis.cpp:120
bool qgsVariantGreaterThan(const QVariant &lhs, const QVariant &rhs)
Compares two QVariant values and returns whether the first is greater than the second.
Definition qgis.cpp:188
QSet< QgsFeatureId > QgsFeatureIds
QList< int > QgsAttributeList
Definition qgsfield.h:27
const QgsCoordinateReferenceSystem & crs