High level wrapper over QgsFeatureRequest

[NathanW2]

The layer iterators are fantastic however the API is pretty raw I think a higher level wrapper to make it a bit more approachable would be nice.

Here is an example in Python that I have done in one my projects:

points = query.From(mylayer).where("valid = True").select("ID", "COL2")

Can be used in line quite nicely in a for loop:

for point in query.From(mylayer).where("valid = True").select("ID", "COL2"):
    pass

Under the hood this just wraps QgsFeatureRequest and handles any of building:

Compared to:

rq = QgsFeatureRequest()
rq.setFilterExpression("valid = True')
rq.setSubsetOfAttributes(["ID", "COL2"], mylayer.pendingFIelds())
for point in mylayer.getFeatures(rq):
    pass

Python version:

class Query(object):
    def __init__(self, layer):
        self.rq = QgsFeatureRequest()
        self.layer = layer

    def where(self, expression):
        self.rq.setFilterExpression(expression)
        return self

    def in_(self, *ids):
        self.rq.setFilterFids(ids)
        return self

    def extent(self, rect):
        self.rq.setFilterRect(rect)
        return self

    def no_geometry(self):
        self.rq.setFlags(QgsFeatureRequest.NoGeometry)
        return self

    def limit(self, top):
        self.rq.setLimit(top)
        return self

    def select(self, *fields, **kwargs):
        if fields:
            self.rq.setSubsetOfAttributes(fields, self.layer.pendingFields())
        if "geometry" in kwargs and not kwargs['geometry']:
            self.no_geometry()

        return self.layer.getFeatures(self.rq)

[wonder-sk]

QgsFeatureRequest could get some love to make it less verbose... but rather than building a wrapper on top of it, maybe better to try to improve existing API...? Something like:

for f in layer.query().filter("x=1").limit(5):
    print f

So layer.query() would replace layer.getFeatures(...) and it would just return QgsFeatureRequest initialized to the given layer, which could have further chained method calls. Then we would just make QgsFeatureRequest an iterable class (in both c++ and python).

Possibly the class name of QgsFeatureRequest could be also changed to QgsFeatureQuery ?

[NathanW2]

Yeah that is fine as well. I was just going with what I already have but the API is more the goal.

…

On Wed, Dec 7, 2016 at 4:51 PM, Martin Dobias ***@***.***> wrote: QgsFeatureRequest could get some love to make it less verbose... but rather than building a wrapper on top of it, maybe better to try to improve existing API...? Something like: for f in layer.query().filter("x=1").limit(5): print f So layer.query() would replace layer.getFeatures(...) and it would just return QgsFeatureRequest initialized to the given layer, which could have further chained method calls. Then we would just make QgsFeatureRequest an iterable class (in both c++ and python). Possibly the class name of QgsFeatureRequest could be also changed to QgsFeatureQuery ? — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#69 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAXS3HbNQe7mxB2F_d5KariC4Kejj5Z3ks5rFleBgaJpZM4LGMHk> .