Hi Lars and other members of this list..
I feel somewhat obligated to help Lars since it's a problem he has
inherited from me. (Sorry about that...)
To sum it up:
If QGIS connects to a WFS based layer from Geoserver using an existing
project with styled layers and one or more layers containing /zero/
objects, QGIS can't determine the object type (point, line-string,
polygon...) for those layers. QGIS will not show legends and promptly
forget any layer information stored in the project related to the
object-type, ex. styling information.
And what is worse - this is a permanent situation: If you save the
project in the above-mentioned state and reopen it at a later time -
where the layers /now/ contains objects - QGIS has forgotten the styling
and other information, so the layers stays invisible and without the
former styling.
(long posting...)
I've done some tests to determine the root cause of this problem:
* Setup of a Postgres database /and /a SQL Server database.
* Loaded the same MapInfo-dataset twice into each database, called
them tableA and tableB, and populated the meta-table
"dbo.geometry_columns" with the correct information for tableA and
tableB in SQLServer.
* Installed a fresh Geoserver 2.15 and MapServer TinyOWS WFS-T server
* Setup a Workspace in Geoserver with 4 layers: tableA and -B from
SQLServer and the same tables from Postgres using WFS.
* In Geoserver, the datastore definition for the SQLServer tables has
a pointer to the "dbo.geometry_columns" meta-table.
* Setup of TinyOWS with tableA and -B from Postgres
* And lastly: Made a project in QGIS 3.4.7 /Windows 64bit with the 6
WFS layers:
o tableA is shown 3 times:
1. From SQLServer through GeoServer;
2. From Postgres through GeoServer
3. From Postgres through Tiny-WFS
o tableB is shown 3 times using the same setup as tableA
All 6 layers in QGIS was shown correctly and the object type for all
layers was recognized.
After this I /deleted/ all rows from tableB in /both/ MS-SQLServer and
in Postgres and reopened the same QGIS project:
* The layer showing (the zero objects) tableB from SQLServer through
GeoServer was not in order.
* The 5 other layers was shown correctly. Legends was correct and
styling was not deleted
I'm drawing the following conclusion:
* GeoServer WFS connections (maybe in conjunction with QGIS) doesn't
work properly when the dataprovider is MS-SQLServer and the layers
contains zero objects. More precisely: GeoServer's SQLServer
dataprovider can't or don't use geometry_columns meta-table defined
in the datastore as described in:
https://docs.geoserver.org/stable/en/user/data/database/sqlserver.html#using-the-geometry-metadata-table
.
After this test I've tried to change the placement and existence of the
"geometry_columns" metadata table:
* No value
* dbo.geometry_column (ordinary placement)
* data.geometry_column (I made a copy of the geometry_columns table
and placed it in the same schema as the test tables)
* geometry_columns (without schema definition)
Nothing of the above worked.
@Lars:
You might change your database system to Postgres and perhaps replace
GeoServer with TinyOWS for WFS purposes (ducks and and run....) .
Or getting the issue investigated and fixed using some GeoServer core
developer, perhaps in cooperation with a QGIS core developer?
Apparently the problem is fixable, since neither TinyOWS or
GeoServer/Postgres have the same issues.
Obviously, the above is a far cry from a really rigorous investigation
of the problem, but it points at some of the "pain" points
Regards
Bo Victor Thomsen
AestasGIS
Denmark
Den 09-05-2019 kl. 13:36 skrev Lars I. Nielsen, LIFA A/S:
Hi developers.
I asked this question on the user’s list, so far without any answers,
but have been advised to ask here as well.
I’m working with a number of projects, which statically open a fixed
number of layers. All layers are fetched using WFS / WFS-T.
Each layer has an extensive rule based styling, and an extensive
field/attribute dialog setup. This is saved in the project files.
Our plugin changes the data provider filter for many layers, when the
user works with the data. These filter expressions are also saved in
the project, of course.
Our problem is, that if the user accidently chooses a work area (= new
data provider filter), which contain no data in any layer, those
layers lose all styling etc. And it’s apparently impossible to recover
these styles etc. by changing the filter back.
So basically the user’s project is unrecoverably trashed at this point
in time.
A - Is this a correct description of how QGIS handles “no-data” layers ?
B - Are there any standard ways to handle this in QGIS (using metadata
or otherwise) in an automated fashion (i.e. not manually) ?
C - If the answers to A and B are yes and no resp., are there any
plans to remedy this unnecessarily serious problem ?
Might it not be solved simply by adding an (optional?) layer metadata
key, that stores the last used topology, and revert to this if no data
are found on the layer ?
Using 3.4.5 x64 (Danish)
Med venlig hilsen
Lars I. Nielsen, LIFA A/S
GIS-konsulent, FME Certified Professional
Beskrivelse: http://website.lifa.dk/lsp.gif
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6313 6800
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6313 6849
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www.lifa.dk <http://www.lifa.dk>
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2492 4866
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20937289
Beskrivelse:
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