Support of WFS attributes aliases

[asaunier]

Some WFS backends such as QGIS Server may provide alias attributes for results of WFS requests. They are made available through a WFS DescribeFeatureType request. For instance:

...
<element alias="Vitesse" type="integer" name="Speed"/>
...

This PR aims to display those aliases if any in the query results window. See https://jira.camptocamp.com/browse/GEORD-21

Still to do:

• get the aliases if any when showing the query results
• support layers added using the WMS browser
• figure out if the code in the gmf.WFSAliases service really deserves a distinct service or if it can be moved for instance to gmf.datasource.DataSourcesManager
• make sure WMS GFI are supported
• tests?

[asaunier]

d93b471 adds attributes aliases to the query results. Problem: original attributes are not removed:

(another problem: the attributes order is not preserved)

How could we remove the original attributes? By creating new features instead of editing the existing one?

Another approach: directly filtering when passing the features to the querywindow partial:

ngeo/contribs/gmf/src/directives/displayquerywindow.js

Lines 450 to 455 in 9da48f8

	gmf.DisplayquerywindowController.prototype.getFeatureValues = function() {
	if (!this.feature) {
	return null;
	}
	return ngeo.FeatureHelper.getFilteredFeatureValues(this.feature);
	};

like in

ngeo/src/services/featurehelper.js

Lines 612 to 618 in 7076508

	ngeo.FeatureHelper.getFilteredFeatureValues = function(feature) {
	const properties = feature.getProperties();
	delete properties['boundedBy'];
	delete properties[feature.getGeometryName()];
	delete properties['ngeo_feature_type_'];
	return properties;
	};

Problem: the list of alias is stored in the dataSource objects and not sure it is available here.

[asaunier]

Thanks to @llienher I have been able to fix the issue reported at #3191 (comment) => aliases are now correctly handled when performing a WFS GetFeature request on a layer available in the application's themes.

I am now investigating the case of external layers added through the "import layer" tool (available in the "desktop_alt" app). As for now I have figured out that:

• only WMS GFI request are supported for external layers, not WFS GetFeature requests (on the other hand it seems "internal" layers are only requested in GMF using WFS GetFeature, right?)
• data sources created by the external datasource manager do not provide ogcServerType info:

  ngeo/contribs/gmf/src/datasource/externaldatasourcesmanager.js

  Lines 351 to 363 in c0f412e

  	dataSource = new ngeo.datasource.OGC({
  	id: id,
  	name: layer['Title'],
  	ogcImageType: ogcImageType,
  	ogcLayers: [{
  	name: layer['Name'],
  	queryable: queryable
  	}],
  	ogcType: ngeo.datasource.OGC.Type.WMS,
  	visible: true,
  	wmsInfoFormat: wmsInfoFormat,
  	wmsUrl: url
  	});

  => the default mapserver type is then always used, including for the "qgisserver" test layer I am using. This is a problem because the aliases are only retrieved for "qgisserver" layers. I have not found how to get the real servertype in this part yet.
• If I force the servertype to "qgisserver", the WFS DescribeFeatureType (required to get the aliases) is blocked saying the WFS requests are not supported for this WMS layer, see https://github.com/camptocamp/ngeo/blob/master/src/services/querent.js#L191-L195 (dataSource.supportsAttributes is false).

[asaunier]

After more investigations about supporting aliases in external layers, I see several problems:

• the ogcServerType is not provided when creating a dataSource for external layers in the gmf.datasource.ExternalDataSourcesManager. Not sure it is easy to have this information (for internal layers, the server type is provided by the "themes" service I think).
• external layers are imported as WMS layers, with no WFS support by default: when trying to make the WFS DescribeFeatureType request to get the list of attributes and aliases, the querent fails because the data source does not support WFS (no wfsUrl), see
  

  ngeo/src/services/querent.js

  Lines 189 to 195 in c0f412e

  	wfsDescribeFeatureType(dataSource) {
  	goog.asserts.assert(
  	dataSource.supportsAttributes,
  	`The data source must support WFS, have a single OGCLayer that
  	is queryable in order to issue WFS DescribeFeatureType requests`
  	);

  and
  

  ngeo/src/datasource/ogc.js

  Lines 714 to 737 in c0f412e

  	get supportsWFS() {
  	return this.wfsUrl !== undefined;
  	}
  	/**
  	* To be able to do advanced operations on a data source, such as editing
  	* or filtering, a data source must be bound to 1 set of attributes.
  	* These attributes are the ones defined by an ogcLayer. This means that
  	* to be considered to support having attributes defined, you either need
  	* to define them directly when creating the data source, or if you let
  	* the querent service get them for you using a WFS DescribeFeatureType
  	* request, the data source must have only 1 ogcLayer set, which must
  	* be queryable.
  	* @return {boolean} Supports attributes.
  	* @export
  	*/
  	get supportsAttributes() {
  	return this.attributes !== null || (
  	this.supportsWFS &&
  	this.ogcLayers !== null &&
  	this.ogcLayers.length === 1 &&
  	this.ogcLayers[0].queryable === true
  	);
  	}

Perhaps we could give up the support of aliases for external layers? At least in a first version of the tool.