QGIS API Documentation 3.27.0-Master (0a97e3138f)
qgsfeatureiterator.cpp
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1/***************************************************************************
2 qgsfeatureiterator.cpp
3 ---------------------
4 begin : Juli 2012
5 copyright : (C) 2012 by Martin Dobias
6 email : wonder dot sk at gmail dot com
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#include "qgsfeatureiterator.h"
16#include "qgslogger.h"
17
18#include "qgssimplifymethod.h"
19#include "qgsexception.h"
20#include "qgslinestring.h"
22#include "qgsfeedback.h"
24
26 : mRequest( request )
27{
28}
29
31{
32 bool dataOk = false;
33 if ( mRequest.limit() >= 0 && mFetchedCount >= mRequest.limit() )
34 {
35 return false;
36 }
37
39 return false;
40
41 if ( mUseCachedFeatures )
42 {
43 if ( mFeatureIterator != mCachedFeatures.constEnd() )
44 {
45 f = mFeatureIterator->mFeature;
46 ++mFeatureIterator;
47 dataOk = true;
48 }
49 else
50 {
51 dataOk = false;
52 // even the zombie dies at this point...
53 mZombie = false;
54 }
55 }
56 else
57 {
58 switch ( mRequest.filterType() )
59 {
61 dataOk = nextFeatureFilterExpression( f );
62 break;
63
65 dataOk = nextFeatureFilterFids( f );
66 break;
67
68 default:
69 dataOk = fetchFeature( f );
70 break;
71 }
72 }
73
74 if ( dataOk )
76
77 return dataOk;
78}
79
81{
82 while ( fetchFeature( f ) )
83 {
86 return true;
87 }
88 return false;
89}
90
92{
93 while ( fetchFeature( f ) )
94 {
95 if ( mRequest.filterFids().contains( f.id() ) )
96 return true;
97 }
98 return false;
99}
100
102{
103 if ( transform.isValid() && feature.hasGeometry() )
104 {
105 try
106 {
107 QgsGeometry g = feature.geometry();
108 g.transform( transform );
109 feature.setGeometry( g );
110 }
111 catch ( QgsCsException & )
112 {
113 // transform error
115 {
116 mRequest.transformErrorCallback()( feature );
117 }
118 // remove geometry - we can't reproject so better not return a geometry in a different crs
119 feature.clearGeometry();
120 }
121 }
122}
123
125{
126 if ( transform.isShortCircuited() )
127 return RequestToSourceCrsResult::Success; // nothing to do
128
129 switch ( request.spatialFilterType() )
130 {
133
135 {
136 QgsRectangle newRect = transform.transformBoundingBox( request.filterRect(), Qgis::TransformDirection::Reverse );
137 request.setFilterRect( newRect );
139 }
141 {
142 // we can't safely handle a distance within query, as we cannot transform the
143 // static within tolerance distance from one CRS to a static distance in a different CRS.
144
145 // in this case we transform the request's distance within requirement to a "worst case" bounding box filter, so
146 // that the request itself can still take advantage of spatial indices even when we have to do the distance within check locally
147 QgsRectangle newRect = transform.transformBoundingBox( request.filterRect(), Qgis::TransformDirection::Reverse );
148 request.setFilterRect( newRect );
149
151 }
152 }
153
155}
156
158{
159 if ( mRequest.filterRect().isNull() )
160 return QgsRectangle();
161
162 QgsCoordinateTransform extentTransform = transform;
163 extentTransform.setBallparkTransformsAreAppropriate( true );
164 return extentTransform.transformBoundingBox( mRequest.filterRect(), Qgis::TransformDirection::Reverse );
165}
166
168{
169 // Prepare if required the simplification of geometries to fetch:
170 // This code runs here because of 'prepareSimplification()' is virtual and it can be overridden
171 // in inherited iterators who change the default behavior.
172 // It would be better to call this method in the constructor enabling virtual-calls as it is described by example at:
173 // http://www.parashift.com/c%2B%2B-faq-lite/calling-virtuals-from-ctor-idiom.html
174 if ( refs == 0 )
175 {
177
178 // Should be called as last preparation step since it possibly will already fetch all features
179 setupOrderBy( mRequest.orderBy() );
180 }
181 refs++;
182}
183
185{
186 refs--;
187 if ( !refs )
188 delete this;
189}
190
192{
193 return mCompileFailed;
194}
195
197{
198 Q_UNUSED( simplifyMethod )
199 return false;
200}
201
202void QgsAbstractFeatureIterator::setupOrderBy( const QList<QgsFeatureRequest::OrderByClause> &orderBys )
203{
204 // Let the provider try using an efficient order by strategy first
205 if ( !orderBys.isEmpty() && !prepareOrderBy( orderBys ) )
206 {
207 // No success from the provider
208
209 // Prepare the expressions
210 QList<QgsFeatureRequest::OrderByClause> preparedOrderBys( orderBys );
211 QList<QgsFeatureRequest::OrderByClause>::iterator orderByIt( preparedOrderBys.begin() );
212
213 QgsExpressionContext *expressionContext( mRequest.expressionContext() );
214 do
215 {
216 orderByIt->prepare( expressionContext );
217 }
218 while ( ++orderByIt != preparedOrderBys.end() );
219
220 // Fetch all features
221 QgsIndexedFeature indexedFeature;
222 indexedFeature.mIndexes.resize( preparedOrderBys.size() );
223
224 while ( nextFeature( indexedFeature.mFeature ) )
225 {
226 expressionContext->setFeature( indexedFeature.mFeature );
227 int i = 0;
228 const auto constPreparedOrderBys = preparedOrderBys;
229 for ( const QgsFeatureRequest::OrderByClause &orderBy : constPreparedOrderBys )
230 {
231 indexedFeature.mIndexes.replace( i++, orderBy.expression().evaluate( expressionContext ) );
232 }
233
234 // We need all features, to ignore the limit for this pre-fetch
235 // keep the fetched count at 0.
236 mFetchedCount = 0;
237 mCachedFeatures.append( indexedFeature );
238 }
239
240 std::sort( mCachedFeatures.begin(), mCachedFeatures.end(), QgsExpressionSorter( preparedOrderBys ) );
241
242 mFeatureIterator = mCachedFeatures.constBegin();
243 mUseCachedFeatures = true;
244 // The real iterator is closed, we are only serving cached features
245 mZombie = true;
246 }
247}
248
249bool QgsAbstractFeatureIterator::providerCanSimplify( QgsSimplifyMethod::MethodType methodType ) const
250{
251 Q_UNUSED( methodType )
252 return false;
253}
254
255bool QgsAbstractFeatureIterator::prepareOrderBy( const QList<QgsFeatureRequest::OrderByClause> &orderBys )
256{
257 Q_UNUSED( orderBys )
258 return false;
259}
260
262{
263}
264
266
268{
269 if ( this != &other )
270 {
271 if ( mIter )
272 mIter->deref();
273 mIter = other.mIter;
274 if ( mIter )
275 mIter->ref();
276 }
277 return *this;
278}
279
281{
282 return mIter && mIter->isValid();
283}
@ DistanceWithin
Filter by distance to reference geometry.
@ BoundingBox
Filter using a bounding box.
@ NoFilter
No spatial filtering of features.
RequestToSourceCrsResult
Possible results from the updateRequestToSourceCrs() method.
@ Success
Request was successfully updated to the source CRS, or no changes were required.
@ DistanceWithinMustBeCheckedManually
The distance within request cannot be losslessly updated to the source CRS, and callers will need to ...
bool mZombie
A feature iterator may be closed already but still be serving features from the cache.
virtual bool nextFeatureFilterFids(QgsFeature &f)
By default, the iterator will fetch all features and check if the id is in the request.
void geometryToDestinationCrs(QgsFeature &feature, const QgsCoordinateTransform &transform) const
Transforms feature's geometry according to the specified coordinate transform.
virtual void setInterruptionChecker(QgsFeedback *interruptionChecker)
Attach an object that can be queried regularly by the iterator to check if it must stopped.
virtual bool fetchFeature(QgsFeature &f)=0
If you write a feature iterator for your provider, this is the method you need to implement!...
long long mFetchedCount
Number of features already fetched by iterator.
virtual bool prepareSimplification(const QgsSimplifyMethod &simplifyMethod)
Setup the simplification of geometries to fetch using the specified simplify method.
void deref()
Remove reference, delete if refs == 0.
QgsRectangle filterRectToSourceCrs(const QgsCoordinateTransform &transform) const SIP_THROW(QgsCsException)
Returns a rectangle representing the original request's QgsFeatureRequest::filterRect().
QgsFeatureRequest mRequest
A copy of the feature request.
QgsAbstractFeatureIterator(const QgsFeatureRequest &request)
base class constructor - stores the iteration parameters
bool compileFailed() const
Indicator if there was an error when sending the compiled query to the server.
virtual bool isValid() const
Returns if this iterator is valid.
int refs
reference counting (to allow seamless copying of QgsFeatureIterator instances)
virtual bool nextFeature(QgsFeature &f)
fetch next feature, return true on success
RequestToSourceCrsResult updateRequestToSourceCrs(QgsFeatureRequest &request, const QgsCoordinateTransform &transform) const SIP_THROW(QgsCsException)
Update a QgsFeatureRequest so that spatial filters are transformed to the source's coordinate referen...
virtual bool nextFeatureFilterExpression(QgsFeature &f)
By default, the iterator will fetch all features and check if the feature matches the expression.
Class for doing transforms between two map coordinate systems.
void setBallparkTransformsAreAppropriate(bool appropriate)
Sets whether approximate "ballpark" results are appropriate for this coordinate transform.
bool isShortCircuited() const
Returns true if the transform short circuits because the source and destination are equivalent.
bool isValid() const
Returns true if the coordinate transform is valid, ie both the source and destination CRS have been s...
QgsRectangle transformBoundingBox(const QgsRectangle &rectangle, Qgis::TransformDirection direction=Qgis::TransformDirection::Forward, bool handle180Crossover=false) const SIP_THROW(QgsCsException)
Transforms a rectangle from the source CRS to the destination CRS.
Custom exception class for Coordinate Reference System related exceptions.
Definition: qgsexception.h:66
Expression contexts are used to encapsulate the parameters around which a QgsExpression should be eva...
void setFeature(const QgsFeature &feature)
Convenience function for setting a feature for the context.
QVariant evaluate()
Evaluate the feature and return the result.
Wrapper for iterator of features from vector data provider or vector layer.
QgsAbstractFeatureIterator * mIter
QgsFeatureIterator & operator=(const QgsFeatureIterator &other)
bool isValid() const
Will return if this iterator is valid.
The OrderByClause class represents an order by clause for a QgsFeatureRequest.
This class wraps a request for features to a vector layer (or directly its vector data provider).
QgsRectangle filterRect() const
Returns the rectangle from which features will be taken.
QgsFeedback * feedback() const
Returns the feedback object that can be queried regularly by the iterator to check if it should be ca...
long long limit() const
Returns the maximum number of features to request, or -1 if no limit set.
QgsExpressionContext * expressionContext()
Returns the expression context used to evaluate filter expressions.
std::function< void(const QgsFeature &) > transformErrorCallback() const
Returns the callback function to use when encountering a transform error when iterating features and ...
OrderBy orderBy() const
Returns a list of order by clauses specified for this feature request.
QgsExpression * filterExpression() const
Returns the filter expression (if set).
const QgsSimplifyMethod & simplifyMethod() const
Returns the simplification method for geometries that will be fetched.
Qgis::SpatialFilterType spatialFilterType() const
Returns the spatial filter type which is currently set on this request.
FilterType filterType() const
Returns the attribute/ID filter type which is currently set on this request.
@ FilterFids
Filter using feature IDs.
@ FilterExpression
Filter using expression.
const QgsFeatureIds & filterFids() const
Returns the feature IDs that should be fetched.
QgsFeatureRequest & setFilterRect(const QgsRectangle &rectangle)
Sets the rectangle from which features will be taken.
The feature class encapsulates a single feature including its unique ID, geometry and a list of field...
Definition: qgsfeature.h:56
QgsGeometry geometry
Definition: qgsfeature.h:67
void clearGeometry()
Removes any geometry associated with the feature.
Definition: qgsfeature.cpp:184
bool hasGeometry() const
Returns true if the feature has an associated geometry.
Definition: qgsfeature.cpp:230
void setGeometry(const QgsGeometry &geometry)
Set the feature's geometry.
Definition: qgsfeature.cpp:170
Q_GADGET QgsFeatureId id
Definition: qgsfeature.h:64
Base class for feedback objects to be used for cancellation of something running in a worker thread.
Definition: qgsfeedback.h:45
bool isCanceled() const SIP_HOLDGIL
Tells whether the operation has been canceled already.
Definition: qgsfeedback.h:54
A geometry is the spatial representation of a feature.
Definition: qgsgeometry.h:125
Qgis::GeometryOperationResult transform(const QgsCoordinateTransform &ct, Qgis::TransformDirection direction=Qgis::TransformDirection::Forward, bool transformZ=false) SIP_THROW(QgsCsException)
Transforms this geometry as described by the coordinate transform ct.
Temporarily used structure to cache order by information.
QVector< QVariant > mIndexes
A rectangle specified with double values.
Definition: qgsrectangle.h:42
bool isNull() const
Test if the rectangle is null (all coordinates zero or after call to setMinimal()).
Definition: qgsrectangle.h:479
This class contains information about how to simplify geometries fetched from a QgsFeatureIterator.
#define BUILTIN_UNREACHABLE
Definition: qgis.h:3046