Subgroup: Feature
Class: QgsFeatureRequest¶
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class
qgis.core.
QgsFeatureRequest
¶ Bases:
sip.wrapper
construct a default request: for all features get attributes and geometries
QgsFeatureRequest(fid: int) construct a request with feature ID filter
QgsFeatureRequest(fids: object) construct a request with feature ID filter
QgsFeatureRequest(rectangle: QgsRectangle) 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.QgsFeatureRequest(expr: QgsExpression, context: QgsExpressionContext = QgsExpressionContext()) construct a request with a filter expression
QgsFeatureRequest(rh: QgsFeatureRequest) copy constructor
This class wraps a request for features to a vector layer (or directly its vector data provider). The request may apply a filter to fetch only a particular subset of features. Currently supported filters: - no filter - all features are returned - feature id - only feature that matches given feature id is returned - feature ids - only features that match any of the given feature ids are returned - filter expression - only features that match the given filter expression are returned
Additionally a spatial rectangle can be set in combination: Only features that intersect given rectangle should be fetched. For the sake of speed, the intersection is often done only using feature’s bounding box. There is a flag ExactIntersect that makes sure that only intersecting features will be returned.
For efficiency, it is also possible to tell provider that some data is not required: - NoGeometry flag - SubsetOfAttributes flag - SimplifyMethod for geometries to fetch
The options may be chained, e.g.: QgsFeatureRequest().setFilterRect(QgsRectangle(0,0,1,1)).setFlags(QgsFeatureRequest.ExactIntersect)
Examples: - fetch all features: QgsFeatureRequest() - fetch all features, only one attribute QgsFeatureRequest().setSubsetOfAttributes(QStringList(“myfield”), provider->fieldMap()) - fetch all features, without geometries QgsFeatureRequest().setFlags(QgsFeatureRequest.NoGeometry) - fetch only features from particular extent QgsFeatureRequest().setFilterRect(QgsRectangle(0,0,1,1)) - fetch only one feature QgsFeatureRequest().setFilterFid(45)
Methods
acceptFeature
Check if a feature is accepted by this requests filter addOrderBy
Adds a new OrderByClause, appending it as the least important one. combineFilterExpression
Modifies the existing filter expression to add an additional expression filter. connectionTimeout
The timeout for how long we should wait for a connection if none is available from the pool at this moment. destinationCrs
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. disableFilter
Disables filter conditions. expressionContext
Returns the expression context used to evaluate filter expressions. filterExpression
Returns the filter expression if set. filterFid
Get the feature ID that should be fetched. filterFids
Get feature IDs that should be fetched. filterRect
Returns the rectangle from which features will be taken. filterType
Return the filter type which is currently set on this request flags
invalidGeometryCheck
Returns the invalid geometry checking behavior. limit
Returns the maximum number of features to request, or -1 if no limit set. orderBy
Return a list of order by clauses specified for this feature request. setConnectionTimeout
The timeout for how long we should wait for a connection if none is available from the pool at this moment. setDestinationCrs
Sets the destination crs
for feature’s geometries.setExpressionContext
Sets the expression context used to evaluate filter expressions. setFilterExpression
Set the filter expression. setFilterFid
Set feature ID that should be fetched. setFilterFids
Set feature IDs that should be fetched. setFilterRect
Sets the rectangle
from which features will be taken.setFlags
Set flags that affect how features will be fetched setInvalidGeometryCallback
Sets a callback function to use when encountering an invalid geometry and invalidGeometryCheck() is set to GeometryAbortOnInvalid or GeometrySkipInvalid. setInvalidGeometryCheck
Sets invalid geometry checking behavior. setLimit
Set the maximum number of features to request. setOrderBy
Set a list of order by clauses. setSimplifyMethod
Set a simplification method for geometries that will be fetched setSubsetOfAttributes
Set a subset of attributes that will be fetched. setTransformErrorCallback
Sets a callback function to use when encountering a transform error when iterating features and a destinationCrs() is set. simplifyMethod
Get simplification method for geometries that will be fetched subsetOfAttributes
Return the subset of attributes which at least need to be fetched transformContext
Returns the transform context, for use when a destinationCrs() has been set and reprojection is required Signals
Attributes
ALL_ATTRIBUTES
ExactIntersect
FilterExpression
FilterFid
FilterFids
FilterNone
GeometryAbortOnInvalid
GeometryNoCheck
GeometrySkipInvalid
NoFlags
NoGeometry
SubsetOfAttributes
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ALL_ATTRIBUTES
= '#!allattributes!#'¶
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ExactIntersect
= 4¶
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FilterExpression
= 2¶
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FilterFid
= 1¶
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FilterFids
= 3¶
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FilterNone
= 0¶
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class
FilterType
¶ Bases:
int
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class
Flag
¶ Bases:
int
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class
Flags
¶ Bases:
sip.wrapper
QgsFeatureRequest.Flags(Union[QgsFeatureRequest.Flags, QgsFeatureRequest.Flag]) QgsFeatureRequest.Flags(QgsFeatureRequest.Flags)
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GeometryAbortOnInvalid
= 2¶
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GeometryNoCheck
= 0¶
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GeometrySkipInvalid
= 1¶
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class
InvalidGeometryCheck
¶ Bases:
int
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NoFlags
= 0¶
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NoGeometry
= 1¶
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class
OrderBy
¶ Bases:
sip.wrapper
Create a new empty order by
QgsFeatureRequest.OrderBy(other: object) Create a new order by from a list of clauses
QgsFeatureRequest.OrderBy(QgsFeatureRequest.OrderBy)
Represents a list of OrderByClauses, with the most important first and the least important last.
New in version 2.14.
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dump
(self) → str¶ Dumps the content to an SQL equivalent syntax
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list
(self) → List[QgsFeatureRequest.OrderByClause]¶ Get a copy as a list of OrderByClauses
This is only required in Python where the inheritance is not properly propagated and this makes it usable.
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load
(self, elem: QDomElement)¶ Deserialize from XML
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save
(self, elem: QDomElement)¶ Serialize to XML
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usedAttributes
(self) → Set[str]¶ Returns a set of used attributes
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class
OrderByClause
(expression: str, ascending: bool = True)¶ Bases:
sip.wrapper
Creates a new OrderByClause for a
QgsFeatureRequest
Parameters: - expression – The expression to use for ordering
- ascending – If 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
QgsFeatureRequest.OrderByClause(expression: str, ascending: bool, nullsfirst: bool) Creates a new OrderByClause for a
QgsFeatureRequest
Parameters: - expression – The expression to use for ordering
- ascending – If the order should be ascending (1,2,3) or descending (3,2,1)
- nullsfirst – If true, NULLS are at the beginning, if false, NULLS are at the end
QgsFeatureRequest.OrderByClause(expression: QgsExpression, ascending: bool = True) Creates a new OrderByClause for a
QgsFeatureRequest
Parameters: - expression – The expression to use for ordering
- ascending – If 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
QgsFeatureRequest.OrderByClause(expression: QgsExpression, ascending: bool, nullsfirst: bool) Creates a new OrderByClause for a
QgsFeatureRequest
Parameters: - expression – The expression to use for ordering
- ascending – If the order should be ascending (1,2,3) or descending (3,2,1)
- nullsfirst – If true, NULLS are at the beginning, if false, NULLS are at the end
QgsFeatureRequest.OrderByClause(QgsFeatureRequest.OrderByClause)
The OrderByClause class represents an order by clause for a QgsFeatureRequest.
It can be a simple field or an expression. Multiple order by clauses can be added to a QgsFeatureRequest to fine tune the behavior if a single field or expression is not enough to completely specify the required behavior.
If expression compilation is activated in the settings and the expression can be translated for the provider in question, it will be evaluated on provider side. If one of these two premises does not apply, the ordering will take place locally which results in increased memory and CPU usage.
If the ordering is done on strings, the order depends on the system’s locale if the local fallback implementation is used. The order depends on the server system’s locale and implementation if ordering is done on the server.
In case the fallback code needs to be used, a limit set on the request will be respected for the features returned by the iterator but internally all features will be requested from the provider.
New in version 2.14.
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ascending
(self) → bool¶ Order ascending
Returns: If ascending order is requested
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dump
(self) → str¶ Dumps the content to an SQL equivalent
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expression
(self) → QgsExpression¶ The expression
Returns: the expression
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nullsFirst
(self) → bool¶ Set if NULLS should be returned first
Returns: if NULLS should be returned first
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prepare
(self, context: QgsExpressionContext) → bool¶ Prepare the expression with the given context.
See also
New in version 3.0.
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setAscending
(self, ascending: bool)¶ Set if ascending order is requested
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setNullsFirst
(self, nullsFirst: bool)¶ Set if NULLS should be returned first
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SubsetOfAttributes
= 2¶
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acceptFeature
(self, feature: QgsFeature) → bool¶ Check if a feature is accepted by this requests filter
Parameters: feature – The feature which will be tested Returns: true, if the filter accepts the feature New in version 2.1.
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addOrderBy
(self, expression: str, ascending: bool = True) → QgsFeatureRequest¶ Adds a new OrderByClause, appending it as the least important one.
Parameters: - expression – The expression to use for ordering
- ascending – If 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
New in version 2.14.
addOrderBy(self, expression: str, ascending: bool, nullsfirst: bool) -> QgsFeatureRequest Adds a new OrderByClause, appending it as the least important one.
Parameters: - expression – The expression to use for ordering
- ascending – If the order should be ascending (1,2,3) or descending (3,2,1)
- nullsfirst – If true, NULLS are at the beginning, if false, NULLS are at the end
New in version 2.14.
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combineFilterExpression
(self, expression: str) → QgsFeatureRequest¶ 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.
New in version 2.14.
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connectionTimeout
(self) → int¶ The timeout 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.
New in version 3.0.
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destinationCrs
(self) → QgsCoordinateReferenceSystem¶ 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
See also
New in version 3.0.
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disableFilter
(self) → QgsFeatureRequest¶ Disables filter conditions. The spatial filter (filterRect) will be kept in place.
Returns: The object the method is called on for chaining New in version 2.12.
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expressionContext
(self) → QgsExpressionContext¶ Returns the expression context used to evaluate filter expressions.
New in version 2.12.
See also
See also
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filterExpression
(self) → QgsExpression¶ Returns the filter expression if set.
See also
See also
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filterFid
(self) → int¶ Get the feature ID that should be fetched.
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filterFids
(self) → object¶ Get feature IDs that should be fetched.
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filterRect
(self) → QgsRectangle¶ Returns the rectangle from which features will be taken. If the returned rectangle is null, then no filter rectangle is set.
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
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filterType
(self) → QgsFeatureRequest.FilterType¶ Return the filter type which is currently set on this request
Returns: Filter type
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flags
(self) → QgsFeatureRequest.Flags¶
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invalidGeometryCheck
(self) → QgsFeatureRequest.InvalidGeometryCheck¶ Returns the invalid geometry checking behavior.
See also
New in version 3.0.
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limit
(self) → int¶ Returns the maximum number of features to request, or -1 if no limit set.
See also
New in version 2.14.
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orderBy
(self) → QgsFeatureRequest.OrderBy¶ Return a list of order by clauses specified for this feature request.
New in version 2.14.
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setConnectionTimeout
(self, connectionTimeout: int)¶ The timeout 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.
New in version 3.0.
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setDestinationCrs
(self, crs: QgsCoordinateReferenceSystem, context: QgsCoordinateTransformContext) → QgsFeatureRequest¶ 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. Ifcrs
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() 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
New in version 3.0.
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setExpressionContext
(self, context: QgsExpressionContext) → QgsFeatureRequest¶ Sets the expression context used to evaluate filter expressions.
New in version 2.12.
See also
See also
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setFilterExpression
(self, expression: str) → QgsFeatureRequest¶ Set the filter expression. {
QgsExpression
}Parameters: expression – expression string See also
See also
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setFilterFid
(self, fid: int) → QgsFeatureRequest¶ Set feature ID that should be fetched.
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setFilterFids
(self, fids: object) → QgsFeatureRequest¶ Set feature IDs that should be fetched.
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setFilterRect
(self, rectangle: QgsRectangle) → QgsFeatureRequest¶ 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.See also
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setFlags
(self, flags: Union[QgsFeatureRequest.Flags, QgsFeatureRequest.Flag]) → QgsFeatureRequest¶ Set flags that affect how features will be fetched
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setInvalidGeometryCallback
(self, Callable[..., None]) → QgsFeatureRequest¶ 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.
New in version 3.0.
See also
invalidGeometryCallback()
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setInvalidGeometryCheck
(self, check: QgsFeatureRequest.InvalidGeometryCheck) → QgsFeatureRequest¶ Sets invalid geometry checking behavior.
Note
Invalid geometry checking is not performed when retrieving features directly from a
QgsVectorDataProvider
.See also
New in version 3.0.
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setLimit
(self, limit: int) → QgsFeatureRequest¶ Set the maximum number of features to request.
Parameters: limit – maximum number of features, or -1 to request all features. See also
New in version 2.14.
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setOrderBy
(self, orderBy: QgsFeatureRequest.OrderBy) → QgsFeatureRequest¶ Set a list of order by clauses.
New in version 2.14.
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setSimplifyMethod
(self, simplifyMethod: QgsSimplifyMethod) → QgsFeatureRequest¶ Set a simplification method for geometries that will be fetched
New in version 2.2.
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setSubsetOfAttributes
(self, attrs: Iterable[int]) → QgsFeatureRequest¶ Set a subset of attributes that will be fetched. Empty list means that all attributes are used. To disable fetching attributes, reset the FetchAttributes flag (which is set by default)
setSubsetOfAttributes(self, attrNames: Iterable[str], fields: QgsFields) -> QgsFeatureRequest Set a subset of attributes by names that will be fetched
setSubsetOfAttributes(self, attrNames: Iterable[str], fields: QgsFields) -> QgsFeatureRequest Set a subset of attributes by names that will be fetched
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setTransformErrorCallback
(self, Callable[..., None]) → QgsFeatureRequest¶ 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.
New in version 3.0.
See also
transformErrorCallback()
See also
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simplifyMethod
(self) → QgsSimplifyMethod¶ Get simplification method for geometries that will be fetched
New in version 2.2.
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subsetOfAttributes
(self) → List[int]¶ Return the subset of attributes which at least need to be fetched
Returns: A list of attributes to be fetched
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transformContext
(self) → QgsCoordinateTransformContext¶ Returns the transform context, for use when a destinationCrs() has been set and reprojection is required
See also
See also
New in version 3.0.
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