Class: QgsExpressionNode¶
- class qgis.core.QgsExpressionNode¶
Bases:
sip.wrapper
Abstract base class for all nodes that can appear in an expression.
QgsExpressionNode() Constructor.
QgsExpressionNode(other:
QgsExpressionNode
) Copy constructorMethods
Returns the node's static cached value.
Generate a clone of this node.
Dump this node into a serialized (part) of an expression.
Returns a reference to the simplest node which represents this node, after any compilation optimizations have been applied.
Evaluate this node with the given context and parent.
Returns
True
if the node can be replaced by a static cached value.Returns
True
if this node can be evaluated for a static value.Abstract virtual method which returns if the geometry is required to evaluate this expression.
Gets the type of this node.
Prepare this node for evaluation.
Abstract virtual method which returns a list of columns required to evaluate this node.
Returns a set of all functions which are used in this expression.
Returns a set of all variables which are used in this expression.
Attributes
- class NamedNode(name: str, node: QgsExpressionNode)¶
Bases:
sip.wrapper
Constructor for NamedNode
- Parameters
name – node name
node – node
QgsExpressionNode.NamedNode(QgsExpressionNode.NamedNode)
- name¶
- node¶
- class NodeList¶
Bases:
sip.wrapper
A list of expression nodes.
- append(self, node: QgsExpressionNode)¶
Takes ownership of the provided node
append(self, node: QgsExpressionNode.NamedNode) Adds a named node. Takes ownership of the provided node.
New in version 2.16.
- Parameters
node (QgsExpressionNode) –
- at(self, i: int) QgsExpressionNode ¶
Gets the node at position i in the list.
New in version 3.0.
- Parameters
i (int) –
- Return type
- clone(self) QgsExpressionNode.NodeList ¶
Creates a deep copy of this list. Ownership is transferred to the caller
- Return type
- count(self) int ¶
Returns the number of nodes in the list.
- Return type
int
- dump(self) str ¶
Returns a string dump of the expression node.
- Return type
str
- hasNamedNodes(self) bool ¶
Returns
True
if list contains any named nodesNew in version 2.16.
- Return type
bool
- list(self) List[QgsExpressionNode] ¶
Gets a list of all the nodes.
- Return type
List[QgsExpressionNode]
- names(self) List[str] ¶
Returns a list of names for nodes. Unnamed nodes will be indicated by an empty string in the list.
New in version 2.16.
- Return type
List[str]
- class NodeType¶
Bases:
int
- cachedStaticValue(self) Any ¶
Returns the node’s static cached value. Only valid if
hasCachedStaticValue()
isTrue
.See also
New in version 3.18.
- Return type
Any
- clone(self) QgsExpressionNode ¶
Generate a clone of this node. Ownership is transferred to the caller.
- Return type
- Returns
a deep copy of this node.
- dump(self) str ¶
Dump this node into a serialized (part) of an expression. The returned expression does not necessarily literally match the original expression, it’s just guaranteed to behave the same way.
- Return type
str
- effectiveNode(self) QgsExpressionNode ¶
Returns a reference to the simplest node which represents this node, after any compilation optimizations have been applied.
Eg. a node like “CASE WHEN true THEN “some_field” WHEN other condition THEN … END” can effectively be replaced entirely by a
QgsExpressionNodeColumnRef
referencing the “some_field” field, as the CASE WHEN … will ALWAYS evaluate to “some_field”.Returns a reference to the current object if no optimizations were applied.
New in version 3.20.
- Return type
- eval(self, parent: QgsExpression, context: QgsExpressionContext) Any ¶
Evaluate this node with the given context and parent. This will return a cached value if it has been determined to be static during the
prepare()
execution.New in version 2.12.
- Parameters
parent (QgsExpression) –
context (QgsExpressionContext) –
- Return type
Any
- hasCachedStaticValue(self) bool ¶
Returns
True
if the node can be replaced by a static cached value.See also
New in version 3.18.
- Return type
bool
- isStatic(self, parent: QgsExpression, context: QgsExpressionContext) bool ¶
Returns
True
if this node can be evaluated for a static value. This is used during theprepare()
step and in case it returnsTrue
, the value of this node will already be evaluated and the result cached (and therefore not re-evaluated in subsequent calls toeval()
). In case this returnsTrue
,prepareNode()
will never be called.New in version 3.0.
- Parameters
parent (QgsExpression) –
context (QgsExpressionContext) –
- Return type
bool
- needsGeometry(self) bool ¶
Abstract virtual method which returns if the geometry is required to evaluate this expression.
This needs to call :py:func:`~QgsExpressionNode.needsGeometry` recursively on any child nodes.
- Return type
bool
- Returns
True
if a geometry is required to evaluate this expression
- nodeType(self) QgsExpressionNode.NodeType ¶
Gets the type of this node.
- Return type
- Returns
The type of this node
- ntBinaryOperator = 1¶
- ntColumnRef = 5¶
- ntCondition = 6¶
- ntFunction = 3¶
- ntInOperator = 2¶
- ntIndexOperator = 7¶
- ntLiteral = 4¶
- ntUnaryOperator = 0¶
- parserFirstColumn¶
- parserFirstLine¶
- parserLastColumn¶
- parserLastLine¶
- prepare(self, parent: QgsExpression, context: QgsExpressionContext) bool ¶
Prepare this node for evaluation. This will check if the node content is static and in this case cache the value. If it’s not static it will call
prepareNode()
to allow the node to do initialization work like for example resolving a column name to an attribute index.New in version 2.12.
- Parameters
parent (QgsExpression) –
context (QgsExpressionContext) –
- Return type
bool
- referencedColumns(self) Set[str] ¶
Abstract virtual method which returns a list of columns required to evaluate this node.
When reimplementing this, you need to return any column that is required to evaluate this node and in addition recursively collect all the columns required to evaluate child nodes.
Warning
If the expression has been prepared via a call to
QgsExpression.prepare()
, or a call toQgsExpressionNode.prepare()
for a node has been made, then some nodes in the expression may have been determined to evaluate to a static pre-calculatable value. In this case the results will omit attribute indices which are used by these pre-calculated nodes, regardless of their actual referenced columns. If you are seeking to use these functions to introspect an expression you must take care to do this with an unprepared expression node.- Return type
Set[str]
- Returns
A list of columns required to evaluate this expression
- referencedFunctions(self) Set[str] ¶
Returns a set of all functions which are used in this expression.
Note
In contrast to the
referencedColumns()
function this method is not affected by any previous calls toQgsExpressionNode.prepare()
.- Return type
Set[str]
- referencedVariables(self) Set[str] ¶
Returns a set of all variables which are used in this expression.
Note
In contrast to the
referencedColumns()
function this method is not affected by any previous calls toQgsExpressionNode.prepare()
.- Return type
Set[str]