def expression_eval(expression_text,
project_id=None,
qgs_layer_id=None,
form_data=None,
formatter=0):
"""Evaluates a QgsExpression and returns the result
:param expression_text: The QgsExpression text
:type expression_text: str
:param project_id: ID of the qdjango project, defaults to None
:type project_id: int, optional
:param qgs_layer_id: ID of the QGIS Layer, defaults to None
:type qgslayer_id: str, optional
:param form_data: A dictionary that maps to a GeoJSON representation of the feature currently edited in the form
:type form_data: dict, optional
:param formatter: Indicate if form_data values contains formatter values or original features value.
:type formatter: int, optional
"""
expression = QgsExpression(expression_text)
expression_context = QgsExpressionContext()
layer = None
for func_name in expression.referencedFunctions():
if func_name in FORBIDDEN_FUNCTIONS:
raise ExpressionForbiddenError(
_('Function "{}" is not allowed for security reasons!').format(
func_name))
for var_name in expression.referencedVariables():
if var_name in FORBIDDEN_VARIABLES:
raise ExpressionForbiddenError(
_('Variable "{}" is not allowed for security reasons!').format(
var_name))
if project_id is not None:
try:
project = Project.objects.get(pk=project_id)
if qgs_layer_id is not None:
try:
layer = project.layer_set.get(qgs_layer_id=qgs_layer_id)
except Layer.DoesNotExist:
raise ExpressionLayerError(
_('QGIS layer with id "{}" could not be found!').
format(qgs_layer_id))
expression_contex = QgsExpressionContextUtils.globalProjectLayerScopes(
layer.qgis_layer)
else:
expression_contex = QgsExpressionContextUtils.globalScope()
expression_context.appendScope(
QgsExpressionContextUtils.projectScope(
project.qgis_project))
except Project.DoesNotExist:
raise ExpressionProjectError(
_('QDjango project with id "{}" could not be found!').format(
project_id))
else:
expression_contex = QgsExpressionContextUtils.globalScope()
if form_data is not None:
if layer is None:
raise ExpressionLayerError(
_('A valid QGIS layer is required to process form data!'))
try:
# Case by formatter
# formatter == 1 : get featureid from layer, usually must be used with formatter form_data
# formatter == 0 : default behavior
if formatter == 0:
fields = layer.qgis_layer.fields()
form_feature = QgsJsonUtils.stringToFeatureList(
json.dumps(form_data), fields, None)[0]
# Set attributes manually because QgsJsonUtils does not respect order
for k, v in form_data['properties'].items():
form_feature.setAttribute(k, v)
else:
qgis_feature_request = QgsFeatureRequest()
exp = expression_from_server_fids(
[form_data['id']], layer.qgis_layer.dataProvider())
qgis_feature_request.combineFilterExpression(exp)
form_feature = get_qgis_features(layer.qgis_layer,
qgis_feature_request)[0]
expression_context.appendScope(
QgsExpressionContextUtils.formScope(form_feature))
expression_context.setFeature(form_feature)
except:
raise ExpressionFormDataError()
valid, errors = expression.checkExpression(expression_text,
expression_context)
if not valid:
raise ExpressionParseError(errors)
result = expression.evaluate(expression_context)
if expression.hasEvalError():
raise ExpressionEvalError(expression.evalErrorString())
return result
def calculate_node(
node, node_attr_name, node_attr_id, layer, discarded_feats):
operator = node.get('operator', DEFAULT_OPERATOR)
# for backwards compatibility, we treat the old
# 'Use a custom field (no recalculation) as the new one with no parentheses
if operator in (OPERATORS_DICT['CUSTOM'],
'Use a custom field (no recalculation)'):
customFormula = node.get('customFormula', '')
expression = QgsExpression(customFormula)
valid, err_msg = QgsExpression.checkExpression(customFormula, None)
if not valid:
raise InvalidFormula(
'Invalid formula "%s": %s' % (customFormula, err_msg))
if customFormula == '':
# use the custom field values instead of recalculating them
request = QgsFeatureRequest().setFlags(
QgsFeatureRequest.NoGeometry).setSubsetOfAttributes(
[node['field']], layer.fields())
for feat in layer.getFeatures(request):
if feat[node['field']] == NULL:
discard_feat = True
discarded_feat = DiscardedFeature(
feat.id(), 'Missing value')
discarded_feats.add(discarded_feat)
return discarded_feats
else:
# attempt to retrieve a formula from the description and to
# calculate the field values based on that formula
context = QgsExpressionContext()
context.appendScope(QgsExpressionContextUtils.layerScope(layer))
expression.prepare(context)
request = QgsFeatureRequest().setFlags(
QgsFeatureRequest.NoGeometry)
with edit(layer):
for feat in layer.getFeatures(request):
context.setFeature(feat)
value = expression.evaluate(context)
if expression.hasEvalError():
raise ValueError(expression.evalErrorString())
if value == NULL:
discard_feat = True
discarded_feat = DiscardedFeature(
feat.id(), 'Missing value')
discarded_feats.add(discarded_feat)
layer.changeAttributeValue(feat.id(), node_attr_id, value)
return discarded_feats
# the existance of children should already be checked
children = node['children']
with edit(layer):
request = QgsFeatureRequest().setFlags(QgsFeatureRequest.NoGeometry)
for feat in layer.getFeatures(request):
# If a feature contains any NULL value, discard_feat will
# be set to True and the corresponding node value will be
# set to NULL
discard_feat = False
feat_id = feat.id()
# init node_value to the correct value depending on the
# node's operator
if operator in SUM_BASED_OPERATORS:
node_value = 0
elif operator in MUL_BASED_OPERATORS:
node_value = 1
else:
raise InvalidOperator('Invalid operator: %s' % operator)
for child in children:
if 'field' not in child:
raise InvalidChild()
# for instance, if the RI can't be calculated, then
# also the IRI can't be calculated
# But it shouldn't happen, because all the children
# should be previously linked to corresponding fields
if feat[child['field']] == NULL:
discard_feat = True
discarded_feat = DiscardedFeature(feat_id, 'Missing value')
discarded_feats.add(discarded_feat)
break # proceed to the next feature
# multiply a variable by -1 if it isInverted
try:
inversion_factor = -1 if child['isInverted'] else 1
except KeyError: # child is not inverted
inversion_factor = 1
if operator in IGNORING_WEIGHT_OPERATORS:
# although these operators ignore weights, they
# take into account the inversion
child_weighted = \
feat[child['field']] * inversion_factor
else: # also multiply by the weight
child_weighted = (
child['weight'] *
feat[child['field']] * inversion_factor)
if operator in SUM_BASED_OPERATORS:
node_value += child_weighted
elif operator in MUL_BASED_OPERATORS:
node_value *= child_weighted
else:
error_message = 'Invalid operator: %s' % operator
raise RuntimeError(error_message)
if discard_feat:
node_value = NULL
elif operator == OPERATORS_DICT['AVG']:
# it is equivalent to do a weighted sum with equal weights, or
# to do the simple sum (ignoring weights) and dividing by the
# number of children (we use the latter solution)
node_value /= len(children) # for sure, len(children)!=0
elif operator == OPERATORS_DICT['GEOM_MEAN']:
# the geometric mean
# (see http://en.wikipedia.org/wiki/Geometric_mean)
# is the product of the N combined items, elevated by 1/N
try:
# NOTE: in python2 this check was the default. In python3
# it would produce a complex number without raising any
# error
if (node_value < 0
and not (1. / len(children)).is_integer()):
raise ValueError('negative number cannot be raised'
' to a fractional power')
node_value **= 1. / len(children)
except ValueError:
node_value = NULL
discarded_feat = DiscardedFeature(feat_id, 'Invalid value')
discarded_feats.add(discarded_feat)
layer.changeAttributeValue(
feat_id, node_attr_id, node_value)
return discarded_feats
