BaseGeometryWidget is not idempotent

[Mathieu Leplatre]

Currently, the geometry data is serialized as wkt :

​https://github.com/django/django/blob/1.6b2/django/contrib/gis/forms/widgets.py#L69
​https://github.com/django/django/blob/1.6b2/django/contrib/gis/templates/gis/openlayers.html#L20

And is read back here:

​https://github.com/django/django/blob/1.6b2/django/contrib/gis/forms/fields.py#L95

But transform() will fail, because the instantiated Geometry won't have any projection associated (wkt does not carry srid).

`
GEOSException at ...
Calling transform() with no SRID set is not supported
`

​https://github.com/django/django/blob/1.6b2/django/contrib/gis/forms/fields.py#L96

There are several possible solutions :

• Use EWKT instead of WKT
• Add srid=self.map_srid parameter to fromstr() when instantiating GEOSGeometry()
• Concatenate 'SRID=%s' % self.map_srid to the received data (this is currently being done like this in JS in openlayers widget code ​https://github.com/django/django/blob/1.6b2/django/contrib/gis/static/gis/js/OLMapWidget.js#L263-L273)

[Claude Paroz]

What about:

diff --git a/django/contrib/gis/forms/fields.py b/django/contrib/gis/forms/fields.py
index 2fb8b54..04a19fd 100644
--- a/django/contrib/gis/forms/fields.py
+++ b/django/contrib/gis/forms/fields.py
@@ -87,6 +87,8 @@ class GeometryField(forms.Field):
         # Only do a geographic comparison if both values are available
         if initial and data:
             data = fromstr(data)
+            if not data.srid and self.srid:
+                data.srid = self.srid
             data.transform(initial.srid)
             # If the initial value was not added by the browser, the geometry
             # provided may be slightly different, the first time it is saved.

[Mathieu Leplatre]

Hum, unless I don't get it, it's wrong.

In your proposition, you assign the database field srid to the data coming for the widget, whereas you should be using the widget's srid !

Something like this :

::

if not data.srid:

data.srid = self.widget.map_srid

If you want to see another approach, for example, in django-leaflet, I did that to fix that problem:
​https://github.com/makinacorpus/django-leaflet/blob/add_leaflet_form_widget_and_admin/leaflet/templates/leaflet/widget.html#L34
Which is a consequence of the lack of modularity mentionned in #20998: because in this particular case, what is transmitted between the field and and the widgets is EWKT !

[Mathieu Leplatre]

Fix if widget srid != field srid

[Mathieu Leplatre]

Fix if widget srid != field srid

[Mathieu Leplatre]

Since SRID is ignored while parsing GeoJSON ("crs" attribute), this bug prevents from using other serialization format than e/wkt.

Indeed, data coming from widget is read without assigning srid during deserialization. If the serialized format cannot carry it, the resulting geometry has no srid. Which fails at first transform() operation...

[Claude Paroz]

Here's a slightly different patch. I didn't like that we had to reconstruct a Geometry object at two different places in the same file. And I prefer to test the srid after having created the object, because you never know if the client has provided a value containing a parsable srid through a clever thing. Criticism welcome!

[Mathieu Leplatre]

Indeed, it's a lot better to use to_python() ! Great, thanks !

[Claude Paroz <claude@…>]

In dd656073ad80d0e8ec9e9dfea30da75a660d759c:

Fixed #21003 -- Ensured geometry widget return value has SRID

Thanks Mathieu Leplatre for the report and initial patch.

[Claude Paroz <claude@…>]

In 0514fbb2f37b530e46f54e205cb8c9d722e142d6:

[1.6.x] Fixed #21003 -- Ensured geometry widget return value has SRID

Thanks Mathieu Leplatre for the report and initial patch.
Backport of dd656073ad from master.