QGIS API Documentation  3.21.0-Master (5b68dc587e)
Classes | Public Types | Public Member Functions | Static Public Attributes | Protected Attributes | List of all members
QgsFeatureRequest Class Reference

This class wraps a request for features to a vector layer (or directly its vector data provider). More...

#include <qgsfeaturerequest.h>

Classes

class  OrderBy
 Represents a list of OrderByClauses, with the most important first and the least important last. More...
 
class  OrderByClause
 The OrderByClause class represents an order by clause for a QgsFeatureRequest. More...
 

Public Types

enum  FilterType { FilterNone , FilterFid , FilterExpression , FilterFids }
 Types of filters. More...
 
enum  Flag {
  NoFlags = 0 , NoGeometry = 1 , SubsetOfAttributes = 2 , ExactIntersect = 4 ,
  IgnoreStaticNodesDuringExpressionCompilation = 8 , EmbeddedSymbols = 16
}
 
enum  InvalidGeometryCheck { GeometryNoCheck = 0 , GeometrySkipInvalid = 1 , GeometryAbortOnInvalid = 2 }
 Handling of features with invalid geometries. More...
 

Public Member Functions

 QgsFeatureRequest ()
 construct a default request: for all features get attributes and geometries More...
 
 QgsFeatureRequest (const QgsExpression &expr, const QgsExpressionContext &context=QgsExpressionContext())
 construct a request with a filter expression More...
 
 QgsFeatureRequest (const QgsFeatureIds &fids)
 construct a request with feature ID filter More...
 
 QgsFeatureRequest (const QgsFeatureRequest &rh)
 copy constructor More...
 
 QgsFeatureRequest (const QgsRectangle &rectangle)
 Construct a request with rectangle bounding box filter. More...
 
 QgsFeatureRequest (QgsFeatureId fid)
 construct a request with feature ID filter More...
 
 ~QgsFeatureRequest ()
 
bool acceptFeature (const QgsFeature &feature)
 Check if a feature is accepted by this requests filter. More...
 
QgsFeatureRequestaddOrderBy (const QString &expression, bool ascending, bool nullsfirst)
 Adds a new OrderByClause, appending it as the least important one. More...
 
QgsFeatureRequestaddOrderBy (const QString &expression, bool ascending=true)
 Adds a new OrderByClause, appending it as the least important one. More...
 
QgsFeatureRequestcombineFilterExpression (const QString &expression)
 Modifies the existing filter expression to add an additional expression filter. More...
 
Q_DECL_DEPRECATED int connectionTimeout () const
 Returns the timeout (in milliseconds) for how long we should wait for a connection if none is available from the pool at this moment. More...
 
QgsCoordinateReferenceSystem destinationCrs () const
 Returns the destination coordinate reference system for feature's geometries, or an invalid QgsCoordinateReferenceSystem if no reprojection will be done and all features will be left with their original geometry. More...
 
QgsFeatureRequestdisableFilter ()
 Disables any attribute/ID filtering. More...
 
double distanceWithin () const
 Returns the maximum distance from the referenceGeometry() of fetched features, if spatialFilterType() is Qgis::SpatialFilterType::DistanceWithin. More...
 
QgsExpressionContextexpressionContext ()
 Returns the expression context used to evaluate filter expressions. More...
 
QgsFeedbackfeedback () const
 Returns the feedback object that can be queried regularly by the iterator to check if it should be canceled, if set. More...
 
QgsExpressionfilterExpression () const
 Returns the filter expression (if set). More...
 
QgsFeatureId filterFid () const
 Returns the feature ID that should be fetched. More...
 
const QgsFeatureIdsfilterFids () const
 Returns the feature IDs that should be fetched. More...
 
QgsRectangle filterRect () const
 Returns the rectangle from which features will be taken. More...
 
FilterType filterType () const
 Returns the attribute/ID filter type which is currently set on this request. More...
 
Flags flags () const
 Returns the flags which affect how features are fetched. More...
 
std::function< void(const QgsFeature &) > invalidGeometryCallback () const
 Returns the callback function to use when encountering an invalid geometry and invalidGeometryCheck() is set to GeometryAbortOnInvalid or GeometrySkipInvalid. More...
 
InvalidGeometryCheck invalidGeometryCheck () const
 Returns the invalid geometry checking behavior. More...
 
long long limit () const
 Returns the maximum number of features to request, or -1 if no limit set. More...
 
QgsFeatureRequestoperator= (const QgsFeatureRequest &rh)
 Assignment operator. More...
 
OrderBy orderBy () const
 Returns a list of order by clauses specified for this feature request. More...
 
QgsGeometry referenceGeometry () const
 Returns the reference geometry used for spatial filtering of features. More...
 
bool requestMayBeNested () const
 In case this request may be run nested within another already running iteration on the same connection, set this to true. More...
 
Q_DECL_DEPRECATED QgsFeatureRequestsetConnectionTimeout (int connectionTimeout)
 Sets the timeout (in milliseconds) for how long we should wait for a connection if none is available from the pool at this moment. More...
 
QgsFeatureRequestsetDestinationCrs (const QgsCoordinateReferenceSystem &crs, const QgsCoordinateTransformContext &context)
 Sets the destination crs for feature's geometries. More...
 
QgsFeatureRequestsetDistanceWithin (const QgsGeometry &geometry, double distance)
 Sets a reference geometry and a maximum distance from this geometry to retrieve features within. More...
 
QgsFeatureRequestsetExpressionContext (const QgsExpressionContext &context)
 Sets the expression context used to evaluate filter expressions. More...
 
void setFeedback (QgsFeedback *feedback)
 Attach a feedback object that can be queried regularly by the iterator to check if it should be canceled. More...
 
QgsFeatureRequestsetFilterExpression (const QString &expression)
 Set the filter expression. More...
 
QgsFeatureRequestsetFilterFid (QgsFeatureId fid)
 Sets the feature ID that should be fetched. More...
 
QgsFeatureRequestsetFilterFids (const QgsFeatureIds &fids)
 Sets the feature IDs that should be fetched. More...
 
QgsFeatureRequestsetFilterRect (const QgsRectangle &rectangle)
 Sets the rectangle from which features will be taken. More...
 
QgsFeatureRequestsetFlags (QgsFeatureRequest::Flags flags)
 Sets flags that affect how features will be fetched. More...
 
QgsFeatureRequestsetInvalidGeometryCallback (const std::function< void(const QgsFeature &)> &callback)
 Sets a callback function to use when encountering an invalid geometry and invalidGeometryCheck() is set to GeometryAbortOnInvalid or GeometrySkipInvalid. More...
 
QgsFeatureRequestsetInvalidGeometryCheck (InvalidGeometryCheck check)
 Sets invalid geometry checking behavior. More...
 
QgsFeatureRequestsetLimit (long long limit)
 Set the maximum number of features to request. More...
 
QgsFeatureRequestsetNoAttributes ()
 Set that no attributes will be fetched. More...
 
QgsFeatureRequestsetOrderBy (const OrderBy &orderBy)
 Set a list of order by clauses. More...
 
QgsFeatureRequestsetRequestMayBeNested (bool requestMayBeNested)
 In case this request may be run nested within another already running iteration on the same connection, set this to true. More...
 
QgsFeatureRequestsetSimplifyMethod (const QgsSimplifyMethod &simplifyMethod)
 Set a simplification method for geometries that will be fetched. More...
 
QgsFeatureRequestsetSubsetOfAttributes (const QgsAttributeList &attrs)
 Set a subset of attributes that will be fetched. More...
 
QgsFeatureRequestsetSubsetOfAttributes (const QSet< QString > &attrNames, const QgsFields &fields)
 Sets a subset of attributes by names that will be fetched. More...
 
QgsFeatureRequestsetSubsetOfAttributes (const QStringList &attrNames, const QgsFields &fields)
 Sets a subset of attributes by names that will be fetched. More...
 
QgsFeatureRequestsetTimeout (int timeout)
 Sets the timeout (in milliseconds) for the maximum time we should wait during feature requests before a feature is returned. More...
 
QgsFeatureRequestsetTransformErrorCallback (const std::function< void(const QgsFeature &)> &callback)
 Sets a callback function to use when encountering a transform error when iterating features and a destinationCrs() is set. More...
 
const QgsSimplifyMethodsimplifyMethod () const
 Returns the simplification method for geometries that will be fetched. More...
 
Qgis::SpatialFilterType spatialFilterType () const
 Returns the spatial filter type which is currently set on this request. More...
 
QgsAttributeList subsetOfAttributes () const
 Returns the subset of attributes which at least need to be fetched. More...
 
int timeout () const
 Returns the timeout (in milliseconds) for the maximum time we should wait during feature requests before a feature is returned. More...
 
QgsCoordinateTransformContext transformContext () const
 Returns the transform context, for use when a destinationCrs() has been set and reprojection is required. More...
 
std::function< void(const QgsFeature &) > transformErrorCallback () const
 Returns the callback function to use when encountering a transform error when iterating features and a destinationCrs() is set. More...
 

Static Public Attributes

static const QString ALL_ATTRIBUTES = QStringLiteral( "#!allattributes!#" )
 A special attribute that if set matches all attributes. More...
 

Protected Attributes

QgsAttributeList mAttrs
 
QgsCoordinateReferenceSystem mCrs
 
double mDistanceWithin = 0
 Maximum distance from reference geometry. More...
 
QgsExpressionContext mExpressionContext
 
QgsFeedbackmFeedback = nullptr
 
FilterType mFilter = FilterNone
 Attribute/ID filter type. More...
 
std::unique_ptr< QgsExpressionmFilterExpression
 
QgsFeatureId mFilterFid = -1
 
QgsFeatureIds mFilterFids
 
QgsRectangle mFilterRect
 Bounding box for spatial filtering. More...
 
Flags mFlags = Flags()
 
std::function< void(const QgsFeature &) > mInvalidGeometryCallback
 
InvalidGeometryCheck mInvalidGeometryFilter = GeometryNoCheck
 
long long mLimit = -1
 
OrderBy mOrderBy
 
QgsGeometry mReferenceGeometry
 Reference geometry for Qgis::RequestSpatialFilter::DistanceWithin filtering. More...
 
std::unique_ptr< QgsGeometryEnginemReferenceGeometryEngine
 Prepared geometry engine for mReferenceGeometry. More...
 
int mRequestMayBeNested = false
 
QgsSimplifyMethod mSimplifyMethod
 
Qgis::SpatialFilterType mSpatialFilter = Qgis::SpatialFilterType::NoFilter
 Spatial filter type. More...
 
int mTimeout = -1
 
QgsCoordinateTransformContext mTransformContext
 
std::function< void(const QgsFeature &) > mTransformErrorCallback
 

Detailed Description

This class wraps a request for features to a vector layer (or directly its vector data provider).

The request may apply an attribute/ID filter to fetch only a particular subset of features. Currently supported filters:

Additionally a spatial filter can be set in combination with the attribute/ID filter. Supported spatial filters are:

For efficiency, it is also possible to tell provider that some data is not required:

The options may be chained, e.g.:

QgsFeatureRequest().setFilterRect(QgsRectangle(0,0,1,1)).setFlags(QgsFeatureRequest.ExactIntersect)
This class wraps a request for features to a vector layer (or directly its vector data provider).
A rectangle specified with double values.
Definition: qgsrectangle.h:42

Examples:

# fetch all features:
# fetch all features, only one attribute
QgsFeatureRequest().setSubsetOfAttributes(['myfield'], layer.fields())
# fetch all features, without geometries
QgsFeatureRequest().setFlags(QgsFeatureRequest.NoGeometry)
# fetch only features from particular extent
QgsFeatureRequest().setFilterRect(QgsRectangle(0,0,1,1))
# fetch only features from particular extent, where the 'type' attribute is equal to 'road':
QgsFeatureRequest().setFilterRect(QgsRectangle(0,0,1,1)).setFilterExpression('"type"=\'road\'')
# fetch only one feature
QgsFeatureRequest().setFilterFid(45)
# fetch features within 50 map units of a linestring geometry
QgsFeatureRequest().setDistanceWithin(QgsGeometry.fromWkt('LineString(0 0, 10 0, 12 1)'), 50)
static QgsGeometry fromWkt(const QString &wkt)
Creates a new geometry from a WKT string.

Definition at line 83 of file qgsfeaturerequest.h.

Member Enumeration Documentation

◆ FilterType

Types of filters.

Enumerator
FilterNone 

No filter is applied.

FilterFid 

Filter using feature ID.

FilterExpression 

Filter using expression.

FilterFids 

Filter using feature IDs.

Definition at line 100 of file qgsfeaturerequest.h.

◆ Flag

Enumerator
NoFlags 
NoGeometry 

Geometry is not required. It may still be returned if e.g. required for a filter condition.

SubsetOfAttributes 

Fetch only a subset of attributes (setSubsetOfAttributes sets this flag)

ExactIntersect 

Use exact geometry intersection (slower) instead of bounding boxes.

IgnoreStaticNodesDuringExpressionCompilation 

If a feature request uses a filter expression which can be partially precalculated due to static nodes in the expression, setting this flag will prevent these precalculated values from being utilized during compilation of the filter for the backend provider. This flag significantly slows down feature requests and should be used for debugging purposes only. (Since QGIS 3.18)

EmbeddedSymbols 

Retrieve any embedded feature symbology (since QGIS 3.20)

Definition at line 86 of file qgsfeaturerequest.h.

◆ InvalidGeometryCheck

Handling of features with invalid geometries.

Enumerator
GeometryNoCheck 

No invalid geometry checking.

GeometrySkipInvalid 

Skip any features with invalid geometry. This requires a slow geometry validity check for every feature.

GeometryAbortOnInvalid 

Close iterator on encountering any features with invalid geometry. This requires a slow geometry validity check for every feature.

Definition at line 109 of file qgsfeaturerequest.h.

Constructor & Destructor Documentation

◆ QgsFeatureRequest() [1/6]

QgsFeatureRequest::QgsFeatureRequest ( )

construct a default request: for all features get attributes and geometries

Definition at line 26 of file qgsfeaturerequest.cpp.

◆ QgsFeatureRequest() [2/6]

QgsFeatureRequest::QgsFeatureRequest ( QgsFeatureId  fid)
explicit

construct a request with feature ID filter

Definition at line 32 of file qgsfeaturerequest.cpp.

◆ QgsFeatureRequest() [3/6]

QgsFeatureRequest::QgsFeatureRequest ( const QgsFeatureIds fids)
explicit

construct a request with feature ID filter

Definition at line 38 of file qgsfeaturerequest.cpp.

◆ QgsFeatureRequest() [4/6]

QgsFeatureRequest::QgsFeatureRequest ( const QgsRectangle rectangle)
explicit

Construct a request with rectangle bounding box filter.

When a destination CRS is set using setDestinationCrs(), rectangle is expected to be in the same CRS as the destinationCrs(). Otherwise, rectangle should use the same CRS as the source layer/provider.

Definition at line 45 of file qgsfeaturerequest.cpp.

◆ QgsFeatureRequest() [5/6]

QgsFeatureRequest::QgsFeatureRequest ( const QgsExpression expr,
const QgsExpressionContext context = QgsExpressionContext() 
)
explicit

construct a request with a filter expression

Definition at line 51 of file qgsfeaturerequest.cpp.

◆ QgsFeatureRequest() [6/6]

QgsFeatureRequest::QgsFeatureRequest ( const QgsFeatureRequest rh)

copy constructor

Definition at line 58 of file qgsfeaturerequest.cpp.

◆ ~QgsFeatureRequest()

QgsFeatureRequest::~QgsFeatureRequest ( )
default

Member Function Documentation

◆ acceptFeature()

bool QgsFeatureRequest::acceptFeature ( const QgsFeature feature)

Check if a feature is accepted by this requests filter.

Parameters
featureThe feature which will be tested
Returns
true, if the filter accepts the feature
Since
QGIS 2.1

Definition at line 318 of file qgsfeaturerequest.cpp.

◆ addOrderBy() [1/2]

QgsFeatureRequest & QgsFeatureRequest::addOrderBy ( const QString &  expression,
bool  ascending,
bool  nullsfirst 
)

Adds a new OrderByClause, appending it as the least important one.

Parameters
expressionThe expression to use for ordering
ascendingIf the order should be ascending (1,2,3) or descending (3,2,1)
nullsfirstIf true, NULLS are at the beginning, if false, NULLS are at the end
Since
QGIS 2.14

Definition at line 203 of file qgsfeaturerequest.cpp.

◆ addOrderBy() [2/2]

QgsFeatureRequest & QgsFeatureRequest::addOrderBy ( const QString &  expression,
bool  ascending = true 
)

Adds a new OrderByClause, appending it as the least important one.

Parameters
expressionThe expression to use for ordering
ascendingIf the order should be ascending (1,2,3) or descending (3,2,1) If the order is ascending, by default nulls are last If the order is descending, by default nulls are first
Since
QGIS 2.14

Definition at line 197 of file qgsfeaturerequest.cpp.

◆ combineFilterExpression()

QgsFeatureRequest & QgsFeatureRequest::combineFilterExpression ( const QString &  expression)

Modifies the existing filter expression to add an additional expression filter.

The filter expressions are combined using AND, so only features matching both the existing expression and the additional expression will be returned.

Calling this method will automatically set filterType() to QgsFeatureRequest::FilterExpression.

Since
QGIS 2.14

Definition at line 178 of file qgsfeaturerequest.cpp.

◆ connectionTimeout()

int QgsFeatureRequest::connectionTimeout ( ) const

Returns the timeout (in milliseconds) for how long we should wait for a connection if none is available from the pool at this moment.

A negative value (which is set by default) will wait forever.

Note
Only works if the provider supports this option.
Deprecated:
Use timeout() instead.
Since
QGIS 3.0

Definition at line 373 of file qgsfeaturerequest.cpp.

◆ destinationCrs()

QgsCoordinateReferenceSystem QgsFeatureRequest::destinationCrs ( ) const

Returns the destination coordinate reference system for feature's geometries, or an invalid QgsCoordinateReferenceSystem if no reprojection will be done and all features will be left with their original geometry.

See also
setDestinationCrs()
transformContext()
Since
QGIS 3.0

Definition at line 295 of file qgsfeaturerequest.cpp.

◆ disableFilter()

QgsFeatureRequest& QgsFeatureRequest::disableFilter ( )
inline

Disables any attribute/ID filtering.

Calling this method will automatically set filterType() to QgsFeatureRequest::FilterNone.

Note
Spatial filters will be left in place.
Returns
The object the method is called on for chaining
Since
QGIS 2.12

Definition at line 567 of file qgsfeaturerequest.h.

◆ distanceWithin()

double QgsFeatureRequest::distanceWithin ( ) const
inline

Returns the maximum distance from the referenceGeometry() of fetched features, if spatialFilterType() is Qgis::SpatialFilterType::DistanceWithin.

When a destination CRS is set using setDestinationCrs(), the distance will be in the spatial units of destinationCrs(). Otherwise, the distance will use the same units as the CRS of the source layer/provider.

See also
setDistanceWithin()
Since
QGIS 3.22

Definition at line 421 of file qgsfeaturerequest.h.

◆ expressionContext()

QgsExpressionContext* QgsFeatureRequest::expressionContext ( )
inline

Returns the expression context used to evaluate filter expressions.

See also
setExpressionContext
filterExpression
Since
QGIS 2.12

Definition at line 546 of file qgsfeaturerequest.h.

◆ feedback()

QgsFeedback * QgsFeatureRequest::feedback ( ) const

Returns the feedback object that can be queried regularly by the iterator to check if it should be canceled, if set.

See also
setFeedback()
Since
QGIS 3.20

Definition at line 411 of file qgsfeaturerequest.cpp.

◆ filterExpression()

QgsExpression* QgsFeatureRequest::filterExpression ( ) const
inline

Returns the filter expression (if set).

See also
setFilterExpression()
expressionContext()

Definition at line 527 of file qgsfeaturerequest.h.

◆ filterFid()

QgsFeatureId QgsFeatureRequest::filterFid ( ) const
inline

Returns the feature ID that should be fetched.

See also
setFilterFid()
filterFids()

Definition at line 439 of file qgsfeaturerequest.h.

◆ filterFids()

const QgsFeatureIds& QgsFeatureRequest::filterFids ( ) const
inline

Returns the feature IDs that should be fetched.

See also
setFilterFids()
filterFid()

Definition at line 457 of file qgsfeaturerequest.h.

◆ filterRect()

QgsRectangle QgsFeatureRequest::filterRect ( ) const

Returns the rectangle from which features will be taken.

If the returned rectangle is null, then no filter rectangle is set.

If spatialFilterType() is Qgis::SpatialFilterType::BoundingBox then only features from within this bounding box will be fetched. If spatialFilterType() is Qgis::SpatialFilterType::DistanceWithin then the returned rectangle represents the bounding box of the referenceGeometry() extended by distanceWithin().

When a destination CRS is set using setDestinationCrs(), the rectangle will be in the same CRS as the destinationCrs(). Otherwise, the rectangle will use the same CRS as the source layer/provider.

See also
setFilterRect()

Definition at line 121 of file qgsfeaturerequest.cpp.

◆ filterType()

FilterType QgsFeatureRequest::filterType ( ) const
inline

Returns the attribute/ID filter type which is currently set on this request.

This type will automatically be set to the appropriate value whenever setFilterFid(), setFilterFids(), setFilterExpression() or disableFilter() are called.

Note
A feature request may have both an attribute/ID filter AND a spatial filter set. See spatialFilterType() to retrieve the spatial filter.
See also
spatialFilterType()

Definition at line 330 of file qgsfeaturerequest.h.

◆ flags()

Flags QgsFeatureRequest::flags ( ) const
inline

Returns the flags which affect how features are fetched.

See also
setFlags()

Definition at line 638 of file qgsfeaturerequest.h.

◆ invalidGeometryCallback()

std::function< void( const QgsFeature & ) > QgsFeatureRequest::invalidGeometryCallback ( ) const
inline

Returns the callback function to use when encountering an invalid geometry and invalidGeometryCheck() is set to GeometryAbortOnInvalid or GeometrySkipInvalid.

Note
not available in Python bindings
See also
setInvalidGeometryCallback()
Since
QGIS 3.0

Definition at line 509 of file qgsfeaturerequest.h.

◆ invalidGeometryCheck()

InvalidGeometryCheck QgsFeatureRequest::invalidGeometryCheck ( ) const
inline

Returns the invalid geometry checking behavior.

See also
setInvalidGeometryCheck()
Since
QGIS 3.0

Definition at line 473 of file qgsfeaturerequest.h.

◆ limit()

long long QgsFeatureRequest::limit ( ) const
inline

Returns the maximum number of features to request, or -1 if no limit set.

See also
setLimit
Since
QGIS 2.14

Definition at line 621 of file qgsfeaturerequest.h.

◆ operator=()

QgsFeatureRequest & QgsFeatureRequest::operator= ( const QgsFeatureRequest rh)

Assignment operator.

Definition at line 63 of file qgsfeaturerequest.cpp.

◆ orderBy()

QgsFeatureRequest::OrderBy QgsFeatureRequest::orderBy ( ) const

Returns a list of order by clauses specified for this feature request.

Since
QGIS 2.14

Definition at line 209 of file qgsfeaturerequest.cpp.

◆ referenceGeometry()

QgsGeometry QgsFeatureRequest::referenceGeometry ( ) const
inline

Returns the reference geometry used for spatial filtering of features.

When spatialFilterType() is Qgis::SpatialFilterType::DistanceWithin then only features within distanceWithin() units of the reference geometry will be fetched.

When a destination CRS is set using setDestinationCrs(), the geometry will be in the same CRS as the destinationCrs(). Otherwise, the geometry will use the same CRS as the source layer/provider.

See also
setDistanceWithin()
Since
QGIS 3.22

Definition at line 408 of file qgsfeaturerequest.h.

◆ requestMayBeNested()

bool QgsFeatureRequest::requestMayBeNested ( ) const

In case this request may be run nested within another already running iteration on the same connection, set this to true.

If this flag is true, this request will be able to make use of "spare" connections to avoid deadlocks.

For example, this should be set on requests that are issued from an expression function.

See also
setRequestMayBeNested()
Since
QGIS 3.4

Definition at line 395 of file qgsfeaturerequest.cpp.

◆ setConnectionTimeout()

QgsFeatureRequest & QgsFeatureRequest::setConnectionTimeout ( int  connectionTimeout)

Sets the timeout (in milliseconds) for how long we should wait for a connection if none is available from the pool at this moment.

A negative value (which is set by default) will wait forever.

Note
Only works if the provider supports this option.
Deprecated:
Use setTimeout() instead.
Since
QGIS 3.0

Definition at line 378 of file qgsfeaturerequest.cpp.

◆ setDestinationCrs()

QgsFeatureRequest & QgsFeatureRequest::setDestinationCrs ( const QgsCoordinateReferenceSystem crs,
const QgsCoordinateTransformContext context 
)

Sets the destination crs for feature's geometries.

If set, all geometries will be reprojected from their original coordinate reference system to this desired reference system. If crs is an invalid QgsCoordinateReferenceSystem then no reprojection will be done and all features will be left with their original geometry.

When a crs is set using setDestinationCrs(), then any filterRect() or referenceGeometry() set on the request is expected to be in the same CRS as the destination CRS.

The feature geometry transformation to the destination CRS is performed after all filter expressions are tested and any virtual fields are calculated. Accordingly, any geometric expressions used in filterExpression() will be performed in the original source CRS. This ensures consistent results are returned regardless of the destination CRS. Similarly, virtual field values will be calculated using the original geometry in the source CRS, so these values are not affected by any destination CRS transform present in the feature request.

See also
destinationCrs()
Since
QGIS 3.0

Definition at line 305 of file qgsfeaturerequest.cpp.

◆ setDistanceWithin()

QgsFeatureRequest & QgsFeatureRequest::setDistanceWithin ( const QgsGeometry geometry,
double  distance 
)

Sets a reference geometry and a maximum distance from this geometry to retrieve features within.

When a destination CRS is set using setDestinationCrs(), geometry is expected to be in the same CRS as the destinationCrs() and distance is in the spatial units of the destinationCrs(). Otherwise, geometry should use the same CRS as the source layer/provider and distance should use the spatial units as this same CRS.

Calling this method will automatically set spatialFilterType() to Qgis::SpatialFilterType::DistanceWithin.

See also
filterRect()
Since
QGIS 3.22

Definition at line 126 of file qgsfeaturerequest.cpp.

◆ setExpressionContext()

QgsFeatureRequest & QgsFeatureRequest::setExpressionContext ( const QgsExpressionContext context)

Sets the expression context used to evaluate filter expressions.

See also
expressionContext
setFilterExpression
Since
QGIS 2.12

Definition at line 191 of file qgsfeaturerequest.cpp.

◆ setFeedback()

void QgsFeatureRequest::setFeedback ( QgsFeedback feedback)

Attach a feedback object that can be queried regularly by the iterator to check if it should be canceled.

Ownership of feedback is NOT transferred, and the caller must take care that it exists for the lifetime of the feature request and feature iterators.

See also
feedback()
Since
QGIS 3.20

Definition at line 406 of file qgsfeaturerequest.cpp.

◆ setFilterExpression()

QgsFeatureRequest & QgsFeatureRequest::setFilterExpression ( const QString &  expression)

Set the filter expression.

{

See also
QgsExpression}
Parameters
expressionexpression string

Calling this method will automatically set filterType() to QgsFeatureRequest::FilterExpression.

See also
filterExpression()
setExpressionContext()

Definition at line 171 of file qgsfeaturerequest.cpp.

◆ setFilterFid()

QgsFeatureRequest & QgsFeatureRequest::setFilterFid ( QgsFeatureId  fid)

Sets the feature ID that should be fetched.

Calling this method will automatically set filterType() to QgsFeatureRequest::FilterFid.

See also
filterFid()
setFilterFids()

Definition at line 145 of file qgsfeaturerequest.cpp.

◆ setFilterFids()

QgsFeatureRequest & QgsFeatureRequest::setFilterFids ( const QgsFeatureIds fids)

Sets the feature IDs that should be fetched.

Calling this method will automatically set filterType() to QgsFeatureRequest::FilterFids.

See also
filterFids()
setFilterFid()

Definition at line 152 of file qgsfeaturerequest.cpp.

◆ setFilterRect()

QgsFeatureRequest & QgsFeatureRequest::setFilterRect ( const QgsRectangle rectangle)

Sets the rectangle from which features will be taken.

An empty rectangle removes the filter.

When a destination CRS is set using setDestinationCrs(), rectangle is expected to be in the same CRS as the destinationCrs(). Otherwise, rectangle should use the same CRS as the source layer/provider.

Calling this method will automatically set spatialFilterType() to Qgis::SpatialFilterType::BoundingBox. If rectangle is a null rectangle then spatialFilterType() will be reset to Qgis::SpatialFilterType::NoFilter.

See also
filterRect()

Definition at line 105 of file qgsfeaturerequest.cpp.

◆ setFlags()

QgsFeatureRequest & QgsFeatureRequest::setFlags ( QgsFeatureRequest::Flags  flags)

Sets flags that affect how features will be fetched.

See also
flags()

Definition at line 226 of file qgsfeaturerequest.cpp.

◆ setInvalidGeometryCallback()

QgsFeatureRequest & QgsFeatureRequest::setInvalidGeometryCallback ( const std::function< void(const QgsFeature &)> &  callback)

Sets a callback function to use when encountering an invalid geometry and invalidGeometryCheck() is set to GeometryAbortOnInvalid or GeometrySkipInvalid.

This function will be called using the feature with invalid geometry as a parameter.

See also
invalidGeometryCallback()
Since
QGIS 3.0

Definition at line 165 of file qgsfeaturerequest.cpp.

◆ setInvalidGeometryCheck()

QgsFeatureRequest & QgsFeatureRequest::setInvalidGeometryCheck ( QgsFeatureRequest::InvalidGeometryCheck  check)

Sets invalid geometry checking behavior.

Note
Invalid geometry checking is not performed when retrieving features directly from a QgsVectorDataProvider.
See also
invalidGeometryCheck()
Since
QGIS 3.0

Definition at line 159 of file qgsfeaturerequest.cpp.

◆ setLimit()

QgsFeatureRequest & QgsFeatureRequest::setLimit ( long long  limit)

Set the maximum number of features to request.

Parameters
limitmaximum number of features, or -1 to request all features.
See also
limit()
Since
QGIS 2.14

Definition at line 220 of file qgsfeaturerequest.cpp.

◆ setNoAttributes()

QgsFeatureRequest & QgsFeatureRequest::setNoAttributes ( )

Set that no attributes will be fetched.

To revert a call to setNoAttributes and fetch all or some available attributes, the SubsetOfAttributes flag should be removed from the request.

Note
This is intended as hint to data providers for optimising feature retrieval. Depending on the provider, it may be trivial for the provider to always return all attributes instead of removing them. In these cases the provider may ignore this hint and return all attributes regardless of whether this method has been called.
See also
setSubsetOfAttributes()
Since
QGIS 3.4

Definition at line 239 of file qgsfeaturerequest.cpp.

◆ setOrderBy()

QgsFeatureRequest & QgsFeatureRequest::setOrderBy ( const OrderBy orderBy)

Set a list of order by clauses.

Since
QGIS 2.14

Definition at line 214 of file qgsfeaturerequest.cpp.

◆ setRequestMayBeNested()

QgsFeatureRequest & QgsFeatureRequest::setRequestMayBeNested ( bool  requestMayBeNested)

In case this request may be run nested within another already running iteration on the same connection, set this to true.

If this flag is true, this request will be able to make use of "spare" connections to avoid deadlocks.

For example, this should be set on requests that are issued from an expression function.

See also
requestMayBeNested()
Since
QGIS 3.4

Definition at line 400 of file qgsfeaturerequest.cpp.

◆ setSimplifyMethod()

QgsFeatureRequest & QgsFeatureRequest::setSimplifyMethod ( const QgsSimplifyMethod simplifyMethod)

Set a simplification method for geometries that will be fetched.

See also
simplifyMethod()
Since
QGIS 2.2

Definition at line 288 of file qgsfeaturerequest.cpp.

◆ setSubsetOfAttributes() [1/3]

QgsFeatureRequest & QgsFeatureRequest::setSubsetOfAttributes ( const QgsAttributeList attrs)

Set a subset of attributes that will be fetched.

An empty attributes list indicates that no attributes will be fetched. To revert a call to setSubsetOfAttributes and fetch all available attributes, the SubsetOfAttributes flag should be removed from the request.

Note
This is intended as hint to data providers for optimising feature retrieval. Depending on the provider, it may be trivial for the provider to always return all attributes instead of the requested subset, or actually result in slower retrieval when the attributes are filtered out. In these cases the provider may ignore this hint and return all attributes regardless of the requested attributes.
See also
subsetOfAttributes()
setNoAttributes()

Definition at line 232 of file qgsfeaturerequest.cpp.

◆ setSubsetOfAttributes() [2/3]

QgsFeatureRequest & QgsFeatureRequest::setSubsetOfAttributes ( const QSet< QString > &  attrNames,
const QgsFields fields 
)

Sets a subset of attributes by names that will be fetched.

Note
This is intended as hint to data providers for optimising feature retrieval. Depending on the provider, it may be trivial for the provider to always return all attributes instead of the requested subset, or actually result in slower retrieval when the attributes are filtered out. In these cases the provider may ignore this hint and return all attributes regardless of the requested attributes.
See also
subsetOfAttributes()

Definition at line 266 of file qgsfeaturerequest.cpp.

◆ setSubsetOfAttributes() [3/3]

QgsFeatureRequest & QgsFeatureRequest::setSubsetOfAttributes ( const QStringList &  attrNames,
const QgsFields fields 
)

Sets a subset of attributes by names that will be fetched.

Note
This is intended as hint to data providers for optimising feature retrieval. Depending on the provider, it may be trivial for the provider to always return all attributes instead of the requested subset, or actually result in slower retrieval when the attributes are filtered out. In these cases the provider may ignore this hint and return all attributes regardless of the requested attributes.
See also
subsetOfAttributes()

Definition at line 244 of file qgsfeaturerequest.cpp.

◆ setTimeout()

QgsFeatureRequest & QgsFeatureRequest::setTimeout ( int  timeout)

Sets the timeout (in milliseconds) for the maximum time we should wait during feature requests before a feature is returned.

A negative value (which is set by default) will wait forever.

Note
Only works if the provider supports this option.
See also
timeout()
Since
QGIS 3.4

Definition at line 389 of file qgsfeaturerequest.cpp.

◆ setTransformErrorCallback()

QgsFeatureRequest & QgsFeatureRequest::setTransformErrorCallback ( const std::function< void(const QgsFeature &)> &  callback)

Sets a callback function to use when encountering a transform error when iterating features and a destinationCrs() is set.

This function will be called using the feature which encountered the transform error as a parameter.

See also
transformErrorCallback()
setDestinationCrs()
Since
QGIS 3.0

Definition at line 312 of file qgsfeaturerequest.cpp.

◆ simplifyMethod()

const QgsSimplifyMethod& QgsFeatureRequest::simplifyMethod ( ) const
inline

Returns the simplification method for geometries that will be fetched.

See also
setSimplifyMethod()
Since
QGIS 2.2

Definition at line 730 of file qgsfeaturerequest.h.

◆ spatialFilterType()

Qgis::SpatialFilterType QgsFeatureRequest::spatialFilterType ( ) const
inline

Returns the spatial filter type which is currently set on this request.

This type will automatically be set to the appropriate value whenever setFilterRect(), or setDistanceWithin() are called.

Note
A feature request may have both an attribute/ID filter AND a spatial filter set. See filterType() to retrieve the attribute/ID filter.
See also
filterType()
Since
QGIS 3.22

Definition at line 344 of file qgsfeaturerequest.h.

◆ subsetOfAttributes()

QgsAttributeList QgsFeatureRequest::subsetOfAttributes ( ) const
inline

Returns the subset of attributes which at least need to be fetched.

Returns
A list of attributes to be fetched
Note
This is intended as hint to data providers for optimising feature retrieval. Depending on the provider, it may be trivial for the provider to always return all attributes instead of the requested subset, or actually result in slower retrieval when the attributes are filtered out. In these cases the provider may ignore this hint and return all attributes regardless of the requested attributes.
See also
setSubsetOfAttributes()
setNoAttributes()

Definition at line 688 of file qgsfeaturerequest.h.

◆ timeout()

int QgsFeatureRequest::timeout ( ) const

Returns the timeout (in milliseconds) for the maximum time we should wait during feature requests before a feature is returned.

A negative value (which is set by default) will wait forever.

Note
Only works if the provider supports this option.
See also
setTimeout()
Since
QGIS 3.4

Definition at line 384 of file qgsfeaturerequest.cpp.

◆ transformContext()

QgsCoordinateTransformContext QgsFeatureRequest::transformContext ( ) const

Returns the transform context, for use when a destinationCrs() has been set and reprojection is required.

See also
setDestinationCrs()
destinationCrs()
Since
QGIS 3.0

Definition at line 300 of file qgsfeaturerequest.cpp.

◆ transformErrorCallback()

std::function< void( const QgsFeature & ) > QgsFeatureRequest::transformErrorCallback ( ) const
inline

Returns the callback function to use when encountering a transform error when iterating features and a destinationCrs() is set.

Note
not available in Python bindings
See also
setTransformErrorCallback()
destinationCrs()
Since
QGIS 3.0

Definition at line 812 of file qgsfeaturerequest.h.

Member Data Documentation

◆ ALL_ATTRIBUTES

const QString QgsFeatureRequest::ALL_ATTRIBUTES = QStringLiteral( "#!allattributes!#" )
static

A special attribute that if set matches all attributes.

Definition at line 292 of file qgsfeaturerequest.h.

◆ mAttrs

QgsAttributeList QgsFeatureRequest::mAttrs
protected

Definition at line 962 of file qgsfeaturerequest.h.

◆ mCrs

QgsCoordinateReferenceSystem QgsFeatureRequest::mCrs
protected

Definition at line 969 of file qgsfeaturerequest.h.

◆ mDistanceWithin

double QgsFeatureRequest::mDistanceWithin = 0
protected

Maximum distance from reference geometry.

Definition at line 955 of file qgsfeaturerequest.h.

◆ mExpressionContext

QgsExpressionContext QgsFeatureRequest::mExpressionContext
protected

Definition at line 960 of file qgsfeaturerequest.h.

◆ mFeedback

QgsFeedback* QgsFeatureRequest::mFeedback = nullptr
protected

Definition at line 973 of file qgsfeaturerequest.h.

◆ mFilter

FilterType QgsFeatureRequest::mFilter = FilterNone
protected

Attribute/ID filter type.

Definition at line 928 of file qgsfeaturerequest.h.

◆ mFilterExpression

std::unique_ptr< QgsExpression > QgsFeatureRequest::mFilterExpression
protected

Definition at line 959 of file qgsfeaturerequest.h.

◆ mFilterFid

QgsFeatureId QgsFeatureRequest::mFilterFid = -1
protected

Definition at line 957 of file qgsfeaturerequest.h.

◆ mFilterFids

QgsFeatureIds QgsFeatureRequest::mFilterFids
protected

Definition at line 958 of file qgsfeaturerequest.h.

◆ mFilterRect

QgsRectangle QgsFeatureRequest::mFilterRect
protected

Bounding box for spatial filtering.

Definition at line 940 of file qgsfeaturerequest.h.

◆ mFlags

Flags QgsFeatureRequest::mFlags = Flags()
protected

Definition at line 961 of file qgsfeaturerequest.h.

◆ mInvalidGeometryCallback

std::function< void( const QgsFeature & ) > QgsFeatureRequest::mInvalidGeometryCallback
protected

Definition at line 967 of file qgsfeaturerequest.h.

◆ mInvalidGeometryFilter

InvalidGeometryCheck QgsFeatureRequest::mInvalidGeometryFilter = GeometryNoCheck
protected

Definition at line 966 of file qgsfeaturerequest.h.

◆ mLimit

long long QgsFeatureRequest::mLimit = -1
protected

Definition at line 964 of file qgsfeaturerequest.h.

◆ mOrderBy

OrderBy QgsFeatureRequest::mOrderBy
protected

Definition at line 965 of file qgsfeaturerequest.h.

◆ mReferenceGeometry

QgsGeometry QgsFeatureRequest::mReferenceGeometry
protected

Reference geometry for Qgis::RequestSpatialFilter::DistanceWithin filtering.

Definition at line 945 of file qgsfeaturerequest.h.

◆ mReferenceGeometryEngine

std::unique_ptr< QgsGeometryEngine > QgsFeatureRequest::mReferenceGeometryEngine
protected

Prepared geometry engine for mReferenceGeometry.

Definition at line 950 of file qgsfeaturerequest.h.

◆ mRequestMayBeNested

int QgsFeatureRequest::mRequestMayBeNested = false
protected

Definition at line 972 of file qgsfeaturerequest.h.

◆ mSimplifyMethod

QgsSimplifyMethod QgsFeatureRequest::mSimplifyMethod
protected

Definition at line 963 of file qgsfeaturerequest.h.

◆ mSpatialFilter

Qgis::SpatialFilterType QgsFeatureRequest::mSpatialFilter = Qgis::SpatialFilterType::NoFilter
protected

Spatial filter type.

Since
QGIS 3.22

Definition at line 935 of file qgsfeaturerequest.h.

◆ mTimeout

int QgsFeatureRequest::mTimeout = -1
protected

Definition at line 971 of file qgsfeaturerequest.h.

◆ mTransformContext

QgsCoordinateTransformContext QgsFeatureRequest::mTransformContext
protected

Definition at line 970 of file qgsfeaturerequest.h.

◆ mTransformErrorCallback

std::function< void( const QgsFeature & ) > QgsFeatureRequest::mTransformErrorCallback
protected

Definition at line 968 of file qgsfeaturerequest.h.


The documentation for this class was generated from the following files: