Class: QgsFeatureRequest¶
-
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 withrectangle
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 expressionQgsFeatureRequest(rh:
QgsFeatureRequest
) copy constructorThis 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(['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 one feature QgsFeatureRequest().setFilterFid(45) .. autoautosummary:: qgis.core.QgsFeatureRequest :enums: :nosignatures: .. autoautosummary:: qgis.core.QgsFeatureRequest :methods: :nosignatures: .. autoautosummary:: qgis.core.QgsFeatureRequest :signals: :nosignatures: .. autoautosummary:: qgis.core.QgsFeatureRequest :attributes:
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ALL_ATTRIBUTES
= '#!allattributes!#'¶
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ExactIntersect
= 4¶
-
FilterExpression
= 2¶
-
FilterFid
= 1¶
-
FilterFids
= 3¶
-
FilterNone
= 0¶
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class
FilterType
¶ Bases:
int
-
class
Flag
¶ Bases:
int
-
class
Flags
¶ Bases:
sip.wrapper
QgsFeatureRequest.Flags(Union[QgsFeatureRequest.Flags, QgsFeatureRequest.Flag]) QgsFeatureRequest.Flags(QgsFeatureRequest.Flags)
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GeometryAbortOnInvalid
= 2¶
-
GeometryNoCheck
= 0¶
-
GeometrySkipInvalid
= 1¶
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class
InvalidGeometryCheck
¶ Bases:
int
-
NoFlags
= 0¶
-
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.
-
dump
(self) → str¶ Dumps the content to an SQL equivalent syntax
- Return type
str
-
list
(self) → List[QgsFeatureRequest.OrderByClause]¶ Gets 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.
- Return type
-
load
(self, elem: QDomElement)¶ Deserialize from XML
- Parameters
elem (QDomElement) –
-
save
(self, elem: QDomElement)¶ Serialize to XML
- Parameters
elem (QDomElement) –
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usedAttributes
(self) → Set[str]¶ Returns a set of used attributes
- Return type
Set[str]
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-
class
OrderByClause
(expression: str, ascending: bool = True)¶ Bases:
sip.wrapper
Creates a new OrderByClause for a
QgsFeatureRequest
- Parameters
expression (str) – The expression to use for ordering
ascending (bool = True) – 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 aQgsFeatureRequest
- 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 aQgsFeatureRequest
- 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.
-
ascending
(self) → bool¶ Order ascending
- Return type
bool
- Returns
If ascending order is requested
-
dump
(self) → str¶ Dumps the content to an SQL equivalent
- Return type
str
-
expression
(self) → QgsExpression¶ The expression
- Return type
- Returns
the expression
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nullsFirst
(self) → bool¶ Set if NULLS should be returned first
- Return type
bool
- 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.
- Parameters
context (QgsExpressionContext) –
- Return type
bool
-
setAscending
(self, ascending: bool)¶ Set if ascending order is requested
- Parameters
ascending (bool) –
-
setNullsFirst
(self, nullsFirst: bool)¶ Set if NULLS should be returned first
- Parameters
nullsFirst (bool) –
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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 (QgsFeature) – The feature which will be tested
- Return type
bool
- Returns
true, if the filter accepts the feature
New in version 2.1.
-
addOrderBy
(self, expression: str, ascending: bool = True) → QgsFeatureRequest¶ Adds a new OrderByClause, appending it as the least important one.
- Parameters
expression (str) – The expression to use for ordering
ascending (bool = True) – 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.
- Return type
-
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.
- Parameters
expression (str) –
- Return type
-
connectionTimeout
(self) → int¶ 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 since version Use: timeout() instead.
New in version 3.0.
- Return type
int
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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.
- Return type
-
disableFilter
(self) → QgsFeatureRequest¶ Disables filter conditions. The spatial filter (filterRect) will be kept in place.
- Return type
- Returns
The object the method is called on for chaining
New in version 2.12.
-
expressionContext
(self) → QgsExpressionContext¶ Returns the expression context used to evaluate filter expressions.
See also
See also
New in version 2.12.
- Return type
-
filterExpression
(self) → QgsExpression¶ Returns the filter expression if set.
See also
See also
- Return type
-
filterFid
(self) → int¶ Gets the feature ID that should be fetched.
- Return type
int
-
filterFids
(self) → object¶ Gets feature IDs that should be fetched.
- Return type
object
-
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
- Return type
-
filterType
(self) → QgsFeatureRequest.FilterType¶ Returns the filter type which is currently set on this request
- Return type
- Returns
Filter type
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flags
(self) → QgsFeatureRequest.Flags¶ - Return type
-
invalidGeometryCheck
(self) → QgsFeatureRequest.InvalidGeometryCheck¶ Returns the invalid geometry checking behavior.
See also
New in version 3.0.
- Return type
-
limit
(self) → int¶ Returns the maximum number of features to request, or -1 if no limit set.
See also
New in version 2.14.
- Return type
int
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orderBy
(self) → QgsFeatureRequest.OrderBy¶ Returns a list of order by clauses specified for this feature request.
New in version 2.14.
- Return type
-
requestMayBeNested
(self) → bool¶ 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.
New in version 3.4.
- Return type
bool
-
setConnectionTimeout
(self, connectionTimeout: int) → QgsFeatureRequest¶ 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 since version Use: setTimeout() instead.
New in version 3.0.
- Parameters
connectionTimeout (int) –
- Return type
-
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 invalidQgsCoordinateReferenceSystem
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.
- Parameters
crs (QgsCoordinateReferenceSystem) –
context (QgsCoordinateTransformContext) –
- Return type
-
setExpressionContext
(self, context: QgsExpressionContext) → QgsFeatureRequest¶ Sets the expression context used to evaluate filter expressions.
See also
See also
New in version 2.12.
- Parameters
context (QgsExpressionContext) –
- Return type
-
setFilterExpression
(self, expression: str) → QgsFeatureRequest¶ Set the filter expression. {
QgsExpression
}- Parameters
expression (str) – expression string
See also
See also
- Return type
-
setFilterFid
(self, fid: int) → QgsFeatureRequest¶ Sets feature ID that should be fetched.
- Parameters
fid (int) –
- Return type
-
setFilterFids
(self, fids: object) → QgsFeatureRequest¶ Sets feature IDs that should be fetched.
- Parameters
fids (object) –
- Return type
-
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
- Parameters
rectangle (QgsRectangle) –
- Return type
-
setFlags
(self, flags: Union[QgsFeatureRequest.Flags, QgsFeatureRequest.Flag]) → QgsFeatureRequest¶ Sets flags that affect how features will be fetched
- Parameters
flags (Union[QgsFeatureRequest.Flags) –
- Return type
-
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.
See also
invalidGeometryCallback()
New in version 3.0.
- Return type
-
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.
- Parameters
check (QgsFeatureRequest.InvalidGeometryCheck) –
- Return type
-
setLimit
(self, limit: int) → QgsFeatureRequest¶ Set the maximum number of features to request.
- Parameters
limit (int) – maximum number of features, or -1 to request all features.
See also
New in version 2.14.
- Return type
-
setNoAttributes
(self) → QgsFeatureRequest¶ 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.
New in version 3.4.
- Return type
-
setOrderBy
(self, orderBy: QgsFeatureRequest.OrderBy) → QgsFeatureRequest¶ Set a list of order by clauses.
New in version 2.14.
- Parameters
orderBy (QgsFeatureRequest.OrderBy) –
- Return type
-
setRequestMayBeNested
(self, requestMayBeNested: bool) → QgsFeatureRequest¶ 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.
New in version 3.4.
- Parameters
requestMayBeNested (bool) –
- Return type
-
setSimplifyMethod
(self, simplifyMethod: QgsSimplifyMethod) → QgsFeatureRequest¶ Set a simplification method for geometries that will be fetched
New in version 2.2.
- Parameters
simplifyMethod (QgsSimplifyMethod) –
- Return type
-
setSubsetOfAttributes
(self, attrs: Iterable[int]) → QgsFeatureRequest¶ 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.
setSubsetOfAttributes(self, attrNames: Iterable[str], fields:
QgsFields
) -> QgsFeatureRequest Sets a subset of attributes by names that will be fetchedsetSubsetOfAttributes(self, attrNames: Iterable[str], fields:
QgsFields
) -> QgsFeatureRequest Sets a subset of attributes by names that will be fetched- Parameters
attrs (Iterable[int]) –
- Return type
-
setTimeout
(self, timeout: int) → QgsFeatureRequest¶ 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.
New in version 3.4.
- Parameters
timeout (int) –
- Return type
-
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.
See also
transformErrorCallback()
See also
New in version 3.0.
- Return type
-
simplifyMethod
(self) → QgsSimplifyMethod¶ Gets simplification method for geometries that will be fetched
New in version 2.2.
- Return type
-
subsetOfAttributes
(self) → List[int]¶ Returns the subset of attributes which at least need to be fetched
- Return type
List[int]
- Returns
A list of attributes to be fetched
-
timeout
(self) → int¶ 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.
New in version 3.4.
- Return type
int
-
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.
- Return type
-