QGIS API Documentation  3.25.0-Master (dec16ba68b)
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"
21 #include "qgsexpressionsorter_p.h"
22 #include "qgsfeedback.h"
23 #include "qgscoordinatetransform.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 )
75  mFetchedCount++;
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 
202 void 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 
249 bool QgsAbstractFeatureIterator::providerCanSimplify( QgsSimplifyMethod::MethodType methodType ) const
250 {
251  Q_UNUSED( methodType )
252  return false;
253 }
254 
255 bool 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).
const QgsSimplifyMethod & simplifyMethod() const
Returns the simplification method for geometries that will be fetched.
QgsRectangle filterRect() const
Returns the rectangle from which features will be taken.
QgsExpression * filterExpression() const
Returns the filter expression (if set).
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.
OrderBy orderBy() const
Returns a list of order by clauses specified for this feature request.
QgsExpressionContext * expressionContext()
Returns the expression context used to evaluate filter expressions.
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.
const QgsFeatureIds & filterFids() const
Returns the feature IDs that should be fetched.
@ FilterFids
Filter using feature IDs.
@ FilterExpression
Filter using expression.
std::function< void(const QgsFeature &) > transformErrorCallback() const
Returns the callback function to use when encountering a transform error when iterating features and ...
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:177
bool hasGeometry() const
Returns true if the feature has an associated geometry.
Definition: qgsfeature.cpp:223
void setGeometry(const QgsGeometry &geometry)
Set the feature's geometry.
Definition: qgsfeature.cpp:163
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:2632