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 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(['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)

.. rubric:: Enums

.. autoautosummary:: qgis.core.QgsFeatureRequest
    :enums:
    :nosignatures:

.. rubric:: Methods

.. autoautosummary:: qgis.core.QgsFeatureRequest
    :methods:
    :nosignatures:

.. rubric:: Signals

.. autoautosummary:: qgis.core.QgsFeatureRequest
    :signals:
    :nosignatures:

.. rubric:: Attributes

.. autoautosummary:: qgis.core.QgsFeatureRequest
    :attributes:

ALL_ATTRIBUTES = '#!allattributes!#'¶

ExactIntersect = 4¶

FilterExpression = 2¶

FilterFid = 1¶

FilterFids = 3¶

FilterNone = 0¶

class FilterType¶: Bases: int

class Flag¶: Bases: int

class Flags¶

Bases: sip.wrapper

QgsFeatureRequest.Flags(Union[QgsFeatureRequest.Flags, QgsFeatureRequest.Flag]) QgsFeatureRequest.Flags(QgsFeatureRequest.Flags)

GeometryAbortOnInvalid = 2¶

GeometryNoCheck = 0¶

GeometrySkipInvalid = 1¶

class InvalidGeometryCheck¶: Bases: int

NoFlags = 0¶

NoGeometry = 1¶

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

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.

load(self, elem: QDomElement)¶: Deserialize from XML

save(self, elem: QDomElement)¶: Serialize to XML

usedAttributes(self) → Set[str]¶: Returns a set of used attributes

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.

ascending(self) → bool¶

Order ascending

Returns: If ascending order is requested

dump(self) → str¶: Dumps the content to an SQL equivalent

expression(self) → QgsExpression¶

The expression

Returns: the expression

nullsFirst(self) → bool¶

Set if NULLS should be returned first

Returns: if NULLS should be returned first

prepare(self, context: QgsExpressionContext) → bool¶: Prepare the expression with the given context.

See also

QgsExpression.prepare()

New in version 3.0.

setAscending(self, ascending: bool)¶: Set if ascending order is requested

setNullsFirst(self, nullsFirst: bool)¶: Set if NULLS should be returned first

SubsetOfAttributes = 2¶

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.

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.

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.

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.

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

setDestinationCrs()

See also

transformContext()

New in version 3.0.

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.

expressionContext(self) → QgsExpressionContext¶: Returns the expression context used to evaluate filter expressions.

See also

setExpressionContext()

See also

filterExpression()

New in version 2.12.

filterExpression(self) → QgsExpression¶: Returns the filter expression if set.

See also

setFilterExpression()

See also

expressionContext()

filterFid(self) → int¶: Gets the feature ID that should be fetched.

filterFids(self) → object¶: Gets feature IDs that should be fetched.

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

setFilterRect()

filterType(self) → QgsFeatureRequest.FilterType¶

Returns the filter type which is currently set on this request

Returns: Filter type

flags(self) → QgsFeatureRequest.Flags¶

invalidGeometryCheck(self) → QgsFeatureRequest.InvalidGeometryCheck¶: Returns the invalid geometry checking behavior.

See also

setInvalidGeometryCheck()

New in version 3.0.

limit(self) → int¶: Returns the maximum number of features to request, or -1 if no limit set.

See also

setLimit()

New in version 2.14.

orderBy(self) → QgsFeatureRequest.OrderBy¶: Returns a list of order by clauses specified for this feature request.

New in version 2.14.

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.

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.

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. 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() 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()

New in version 3.0.

setExpressionContext(self, context: QgsExpressionContext) → QgsFeatureRequest¶: Sets the expression context used to evaluate filter expressions.

See also

expressionContext()

See also

setFilterExpression()

New in version 2.12.

setFilterExpression(self, expression: str) → QgsFeatureRequest¶

Set the filter expression. {QgsExpression}

Parameters: expression – expression string

See also

filterExpression()

See also

setExpressionContext()

setFilterFid(self, fid: int) → QgsFeatureRequest¶: Sets feature ID that should be fetched.

setFilterFids(self, fids: object) → QgsFeatureRequest¶: Sets feature IDs that should be fetched.

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

filterRect()

setFlags(self, flags: Union[QgsFeatureRequest.Flags, QgsFeatureRequest.Flag]) → QgsFeatureRequest¶: Sets flags that affect how features will be fetched

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.

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

invalidGeometryCheck()

New in version 3.0.

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

limit()

New in version 2.14.

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.

setOrderBy(self, orderBy: QgsFeatureRequest.OrderBy) → QgsFeatureRequest¶: Set a list of order by clauses.

New in version 2.14.

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.

setSimplifyMethod(self, simplifyMethod: QgsSimplifyMethod) → QgsFeatureRequest¶: Set a simplification method for geometries that will be fetched

New in version 2.2.

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 fetched

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.

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

setDestinationCrs()

New in version 3.0.

simplifyMethod(self) → QgsSimplifyMethod¶: Gets simplification method for geometries that will be fetched

New in version 2.2.

subsetOfAttributes(self) → List[int]¶

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

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.

transformContext(self) → QgsCoordinateTransformContext¶: Returns the transform context, for use when a destinationCrs() has been set and reprojection is required

See also

setDestinationCrs()

See also

destinationCrs()

New in version 3.0.