This commit adds a number of different forms of aggregates to
the expression engine.
1. Aggregates within the current layer, eg sum("passengers")
Supports sub expressions (ie sum("passengers"/2) ), group by
( sum("passengers", group_by:="line_segment") ), and optional
filters ( sum("passengers", filter:= "station_class" > 3 ) )
2. Relational aggregates, which calculate an aggregate over
all matching child features from a relation, eg
relation_aggregate( 'my_relation', 'mean', "some_child_field" )
3. A summary aggregate function, for calculating aggregates
on other layers. Eg aggregate('rail_station_layer','sum',"passengers")
The summary aggregate function supports an optional filter,
making it possible to calculate things like:
aggregate('rail_stations','sum',"passengers",
intersects(@atlas_geometry, $geometry ) )
for calculating the total number of passengers for the stations
inside the current atlas feature
In all cases the calculations are cached inside the expression
context, so they only need to be calculated once for each
set of expression evaluations.
Sponsored by Kanton of Zug, Switzerland
Can be used to store the results of expensive sub-expression
calculations (eg layer aggregates), so that future expression
evaluation using the same context does not have to recalculate
the cached values.
In https://codereview.qt-project.org/#/c/99815/ implemented in QT 5.5,
doubles are converted to strings using '%.17g', so short decimal values
might be expanded to long strings depending on their values.
https://wiki.qt.io/New_Features_in_Qt_5.7 has a logic to avoid this, but
if we select carefully the double to have both an exact binary and decimal
representation, that can work will all versions.
$ python -c "print('%.17g' % 9.7)"
9.6999999999999993
$ python -c "print('%.17g' % 1.25)"
1.25
Second part of qgis/QGIS-Enhancement-Proposals#53
(QEP 35: WFS provider enhancements)
- URI parameter with sql with SELECT / FROM / JOIN / WHERE / ORDER BY clauses
- handle WFS 2.0 joins
- handle DateTime fields
- enable "Only request features overlapping the view extent" by default (and memorize the settings)
- rework DescribeFeatureType parsing to handle responses with several documents, and some support for attribute types being complexType
- rework feature transfer between downloader and iterator so as to avoid uncontrolled RAM usage when the iterator cannot keep up with the downloader
- turn on WAL journaling for better reader / writer concurrency
- add retry logic based on the 'Max retry in case of tile request errors' setting (renamed 'Max retry in case of tile or feature request errors')
- error to MessageBar in case of failed download
- in progress dialog, add a "Hide" button to mask the dialog
- improve automated testing
- add testing of the GUI of QgsWFSSourceSelect
Move the QgsExpression::Interval class out to its own QgsInterval
class, extend with new methods and add tests
Add a typedef to keep API compatibility for 2.16
This change makes the current atlas feature (and additionally all
attributes of related child features) available to the source of
a composer HTML item, allowing the item to dynamically adjust
its rendered HTML in response to the feature's properties. An
example use case is dynamically populating a HTML table with
all the attributes of related child features for the atlas
feature.
To use this, the HTML source must implement a "setFeature(feature)"
JavaScript function. This function is called whenever the atlas
feature changes, and is passed the atlas feature (+related attributes)
as a GeoJSON Feature.
Sponsored by Kanton of Zug, Switzerland
The previous setting for include WKT when copying features has been
replaced with a choice of copying features as "Plain text, attributes
only", "Plain text, WKT geometry" and a new "GeoJSON" option.
When set to "GeoJSON", copying features in QGIS will place a GeoJSON
text representation of the features on the clipboard for easy
pasting into other applications/javascript code.
Sponsored by North Road
