Number of layers in a group is limited

[sbrunner]

Who requested this new feature?

tadao

Is your feature request related to a problem?

No

Describe the solution you'd like

When a group contains many layers, if the user load all layers of the group, the map is not updated and an error message is sent back to the client by the server:
Request-URI Too Long

The requested URL's length exceeds the capacity limit for this server.

How to see the problem: http://carto.tadao.fr/?lang=fr&baselayer_ref=OSM%20WMTS%20-%20couleur&tree_groups=Tadao&tree_group_layers_Tadao=arret%20scolaire%20ligne%202400%2Citineraire%20scolaire%20ligne%202400%2Carret%20scolaire%20ligne%202401%2Citineraire%20scolaire%20ligne%202401%2Carret%20scolaire%20ligne%202411%2Citineraire%20scolaire%20ligne%202411%2Carret%20scolaire%20ligne%202412%2Citineraire%20scolaire%20ligne%202412%2Carret%20scolaire%20ligne%202500%2Citineraire%20scolaire%20ligne%202500%2Carret%20scolaire%20ligne%202501%2Citineraire%20scolaire%20ligne%202501%2Carret%20scolaire%20ligne%202502%2Citineraire%20scolaire%20ligne%202502%2Carret%20scolaire%20ligne%202504%2Citineraire%20scolaire%20ligne%202504%2Carret%20scolaire%20ligne%202505%2Citineraire%20scolaire%20ligne%202505%2Carret%20scolaire%20ligne%202506%2Citineraire%20scolaire%20ligne%202506%2Carret%20scolaire%20ligne%202507%2Citineraire%20scolaire%20ligne%202507%2Carret%20scolaire%20ligne%202508%2Citineraire%20scolaire%20ligne%202508%2Carret%20scolaire%20ligne%202510%2Citineraire%20scolaire%20ligne%202510%2Carret%20scolaire%20ligne%202511%2Citineraire%20scolaire%20ligne%202511%2Carret%20scolaire%20ligne%202512%2Citineraire%20scolaire%20ligne%202512%2Carret%20scolaire%20ligne%202513%2Citineraire%20scolaire%20ligne%202513%2Carret%20scolaire%20ligne%202515%2Citineraire%20scolaire%20ligne%202515%2Carret%20scolaire%20ligne%202516%2Citineraire%20scolaire%20ligne%202516%2Carret%20scolaire%20ligne%202517%2Citineraire%20scolaire%20ligne%202517%2Carret%20scolaire%20ligne%202519%2Citineraire%20scolaire%20ligne%202519%2Citineraire%20scolaire%20ligne%202520%2Carret%20scolaire%20ligne%202520%2Carret%20scolaire%20ligne%202523%2Citineraire%20scolaire%20ligne%202523%2Carret%20scolaire%20ligne%202524%2Citineraire%20scolaire%20ligne%202524%2Carret%20scolaire%20ligne%202525%2Citineraire%20scolaire%20ligne%202525%2Carret%20scolaire%20ligne%202526%2Citineraire%20scolaire%20ligne%202526%2Carret%20scolaire%20ligne%202527%2Citineraire%20scolaire%20ligne%202527%2Carret%20scolaire%20ligne%202528%2Citineraire%20scolaire%20ligne%202528%2Carret%20scolaire%20ligne%202529%2Citineraire%20scolaire%20ligne%202529%2Carret%20scolaire%20ligne%202530%2Citineraire%20scolaire%20ligne%202530%2Carret%20scolaire%20ligne%202531%2Citineraire%20scolaire%20ligne%202531%2Carret%20scolaire%20ligne%202532%2Citineraire%20scolaire%20ligne%202532%2Carret%20scolaire%20ligne%202533%2Citineraire%20scolaire%20ligne%202533%2Carret%20scolaire%20ligne%202534%2Citineraire%20scolaire%20ligne%202534%2Carret%20scolaire%20ligne%202535%2Citineraire%20scolaire%20ligne%202535%2Carret%20scolaire%20ligne%202550%2Citineraire%20scolaire%20ligne%202550%2Carret%20scolaire%20ligne%202551%2Citineraire%20scolaire%20ligne%202551%2Carret%20scolaire%20ligne%202552%2Citineraire%20scolaire%20ligne%202552%2Carret%20scolaire%20ligne%202553%2Citineraire%20scolaire%20ligne%202553%2Carret%20scolaire%20ligne%202554%2Citineraire%20scolaire%20ligne%202554%2Carret%20scolaire%20ligne%202555%2Citineraire%20scolaire%20ligne%202555%2Carret%20scolaire%20ligne%202556%2Citineraire%20scolaire%20ligne%202556%2Carret%20scolaire%20ligne%202560%2Citineraire%20scolaire%20ligne%202560%2Carret%20scolaire%20ligne%202570%2Citineraire%20scolaire%20ligne%202570%2Carret%20scolaire%20ligne%202600%2Citineraire%20scolaire%20ligne%202600%2Carret%20scolaire%20ligne%202610%2Citineraire%20scolaire%20ligne%202610%2Carret%20scolaire%20ligne%202611%2Citineraire%20scolaire%20ligne%202611%2Carret%20scolaire%20ligne%202612%2Citineraire%20scolaire%20ligne%202612%2Carret%20scolaire%20ligne%202613%2Citineraire%20scolaire%20ligne%202613%2Carret%20scolaire%20ligne%202700%2Citineraire%20scolaire%20ligne%202700%2Carret%20scolaire%20ligne%202701%2Citineraire%20scolaire%20ligne%202701%2Carret%20scolaire%20ligne%202702%2Citineraire%20scolaire%20ligne%202702%2Carret%20scolaire%20ligne%202710%2Citineraire%20scolaire%20ligne%202710%2Carret%20scolaire%20ligne%202711%2Citineraire%20scolaire%20ligne%202711%2Carret%20scolaire%20ligne%202712%2Citineraire%20scolaire%20ligne%202712%2Carret%20scolaire%20ligne%202721%2Citineraire%20scolaire%20ligne%202721%2Carret%20scolaire%20ligne%202722%2Citineraire%20scolaire%20ligne%202722%2Carret%20scolaire%20ligne%202723%2Citineraire%20scolaire%20ligne%202723%2Carret%20scolaire%20ligne%202730%2Citineraire%20scolaire%20ligne%202730%2Carret%20scolaire%20ligne%202731%2Citineraire%20scolaire%20ligne%202731%2Carret%20scolaire%20ligne%202811%2Citineraire%20scolaire%20ligne%202811%2Carret%20scolaire%20ligne%202812%2Citineraire%20scolaire%20ligne%202812%2Carret%20scolaire%20ligne%202820%2Citineraire%20scolaire%20ligne%202820%2Carret%20scolaire%20ligne%202830%2Citineraire%20scolaire%20ligne%202830%2Carret%20scolaire%20ligne%202831%2Citineraire%20scolaire%20ligne%202831%2Carret%20scolaire%20ligne%202832%2Citineraire%20scolaire%20ligne%202832%2Carret%20scolaire%20ligne%202833%2Citineraire%20scolaire%20ligne%202833%2Carret%20scolaire%20ligne%202834%2Citineraire%20scolaire%20ligne%202834%2Carret%20scolaire%20ligne%202835%2Citineraire%20scolaire%20ligne%202835%2Carret%20scolaire%20ligne%202836%2Citineraire%20scolaire%20ligne%202836%2Carret%20scolaire%20ligne%202840%2Citineraire%20scolaire%20ligne%202840%2Carret%20scolaire%20ligne%203000%2Citineraire%20scolaire%20ligne%203000%2Carret%20scolaire%20ligne%203001%2Citineraire%20scolaire%20ligne%203001%2Carret%20scolaire%20ligne%203002%2Citineraire%20scolaire%20ligne%203002%2Carret%20scolaire%20ligne%203003%2Citineraire%20scolaire%20ligne%203003%2Carret%20scolaire%20ligne%203004%2Citineraire%20scolaire%20ligne%203004%2Carret%20scolaire%20ligne%203005%2Citineraire%20scolaire%20ligne%203005%2Carret%20scolaire%20ligne%203006%2Citineraire%20scolaire%20ligne%203006%2Carret%20scolaire%20ligne%203007%2Citineraire%20scolaire%20ligne%203007%2Carret%20scolaire%20ligne%203008%2Citineraire%20scolaire%20ligne%203008%2Carret%20scolaire%20ligne%203009%2Citineraire%20scolaire%20ligne%203009%2Carret%20scolaire%20ligne%203010%2Citineraire%20scolaire%20ligne%203010%2Citineraire%20scolaire%20ligne%202521%2Carret%20scolaire%20ligne%202521%2Carret%20scolaire%20ligne%201121%2Citineraire%20scolaire%20ligne%201121%2Carret%20scolaire%20ligne%201122%2Citineraire%20scolaire%20ligne%201122%2Carret%20scolaire%20ligne%201123%2Citineraire%20scolaire%20ligne%201123%2Carret%20scolaire%20ligne%201130%2Citineraire%20scolaire%20ligne%201130%2Carret%20scolaire%20ligne%201131%2Citineraire%20scolaire%20ligne%201131%2Carret%20scolaire%20ligne%201132%2Citineraire%20scolaire%20ligne%201132%2Carret%20scolaire%20ligne%201133%2Citineraire%20scolaire%20ligne%201133%2Carret%20scolaire%20ligne%201134%2Citineraire%20scolaire%20ligne%201134%2Carret%20scolaire%20ligne%201140%2Citineraire%20scolaire%20ligne%201140%2Carret%20scolaire%20ligne%201200%2Citineraire%20scolaire%20ligne%201200%2Carret%20scolaire%20ligne%201201%2Citineraire%20scolaire%20ligne%201201%2Carret%20scolaire%20ligne%201210%2Citineraire%20scolaire%20ligne%201210%2Carret%20scolaire%20ligne%201211%2Citineraire%20scolaire%20ligne%201211%2Carret%20scolaire%20ligne%201220%2Citineraire%20scolaire%20ligne%201220%2Carret%20scolaire%20ligne%201221%2Citineraire%20scolaire%20ligne%201221%2Carret%20scolaire%20ligne%201222%2Citineraire%20scolaire%20ligne%201222%2Carret%20scolaire%20ligne%201300%2Citineraire%20scolaire%20ligne%201300%2Carret%20scolaire%20ligne%201310%2Citineraire%20scolaire%20ligne%201310%2Carret%20scolaire%20ligne%201311%2Citineraire%20scolaire%20ligne%201311%2Carret%20scolaire%20ligne%201312%2Citineraire%20scolaire%20ligne%201312%2Carret%20scolaire%20ligne%201313%2Citineraire%20scolaire%20ligne%201313%2Carret%20scolaire%20ligne%201314%2Citineraire%20scolaire%20ligne%201314%2Carret%20scolaire%20ligne%201315%2Citineraire%20scolaire%20ligne%201315%2Carret%20scolaire%20ligne%201316%2Citineraire%20scolaire%20ligne%201316%2Carret%20scolaire%20ligne%201317%2Citineraire%20scolaire%20ligne%201317%2Carret%20scolaire%20ligne%201319%2Citineraire%20scolaire%20ligne%201319%2Carret%20scolaire%20ligne%201320%2Citineraire%20scolaire%20ligne%201320%2Carret%20scolaire%20ligne%201321%2Citineraire%20scolaire%20ligne%201321%2Carret%20scolaire%20ligne%201322%2Citineraire%20scolaire%20ligne%201322%2Carret%20scolaire%20ligne%201323%2Citineraire%20scolaire%20ligne%201323%2Carret%20scolaire%20ligne%201324%2Citineraire%20scolaire%20ligne%201324%2Carret%20scolaire%20ligne%201325%2Citineraire%20scolaire%20ligne%201325%2Carret%20scolaire%20ligne%201326%2Citineraire%20scolaire%20ligne%201326%2Carret%20scolaire%20ligne%201327%2Citineraire%20scolaire%20ligne%201327%2Carret%20scolaire%20ligne%201328%2Citineraire%20scolaire%20ligne%201328%2Carret%20scolaire%20ligne%201329%2Citineraire%20scolaire%20ligne%201329%2Carret%20scolaire%20ligne%201330%2Citineraire%20scolaire%20ligne%201330%2Carret%20scolaire%20ligne%201400%2Citineraire%20scolaire%20ligne%201400%2Carret%20scolaire%20ligne%201401%2Citineraire%20scolaire%20ligne%201401%2Carret%20scolaire%20ligne%201402%2Citineraire%20scolaire%20ligne%201402%2Carret%20scolaire%20ligne%201410%2Citineraire%20scolaire%20ligne%201410%2Carret%20scolaire%20ligne%201420%2Citineraire%20scolaire%20ligne%201420%2Carret%20scolaire%20ligne%201430%2Citineraire%20scolaire%20ligne%201430%2Carret%20scolaire%20ligne%201431%2Citineraire%20scolaire%20ligne%201431%2Carret%20scolaire%20ligne%201432%2Citineraire%20scolaire%20ligne%201432%2Carret%20scolaire%20ligne%201433%2Citineraire%20scolaire%20ligne%201433%2Carret%20scolaire%20ligne%201434%2Citineraire%20scolaire%20ligne%201434%2Carret%20scolaire%20ligne%201435%2Citineraire%20scolaire%20ligne%201435%2Carret%20scolaire%20ligne%201436%2Citineraire%20scolaire%20ligne%201436%2Carret%20scolaire%20ligne%201437%2Citineraire%20scolaire%20ligne%201437%2Carret%20scolaire%20ligne%201441%2Citineraire%20scolaire%20ligne%201441%2Carret%20scolaire%20ligne%201442%2Citineraire%20scolaire%20ligne%201442%2Carret%20scolaire%20ligne%201443%2Citineraire%20scolaire%20ligne%201443%2Carret%20scolaire%20ligne%201444%2Citineraire%20scolaire%20ligne%201444%2Carret%20scolaire%20ligne%201450%2Citineraire%20scolaire%20ligne%201450%2Carret%20scolaire%20ligne%201451%2Citineraire%20scolaire%20ligne%201451%2Carret%20scolaire%20ligne%201452%2Citineraire%20scolaire%20ligne%201452%2Carret%20scolaire%20ligne%201453%2Citineraire%20scolaire%20ligne%201453%2Carret%20scolaire%20ligne%201454%2Citineraire%20scolaire%20ligne%201454%2Carret%20scolaire%20ligne%201456%2Citineraire%20scolaire%20ligne%201456%2Carret%20scolaire%20ligne%201457%2Citineraire%20scolaire%20ligne%201457%2Carret%20scolaire%20ligne%201458%2Citineraire%20scolaire%20ligne%201458%2Carret%20scolaire%20ligne%201461%2Citineraire%20scolaire%20ligne%201461%2Carret%20scolaire%20ligne%201462%2Citineraire%20scolaire%20ligne%201462%2Carret%20scolaire%20ligne%201464%2Citineraire%20scolaire%20ligne%201464%2Carret%20scolaire%20ligne%201465%2Citineraire%20scolaire%20ligne%201465%2Carret%20scolaire%20ligne%201466%2Citineraire%20scolaire%20ligne%201466%2Carret%20scolaire%20ligne%201500%2Citineraire%20scolaire%20ligne%201500%2Carret%20scolaire%20ligne%201501%2Citineraire%20scolaire%20ligne%201501%2Carret%20scolaire%20ligne%201502%2Citineraire%20scolaire%20ligne%201502%2Carret%20scolaire%20ligne%201503%2Citineraire%20scolaire%20ligne%201503%2Carret%20scolaire%20ligne%201504%2Citineraire%20scolaire%20ligne%201504%2Carret%20scolaire%20ligne%201505%2Citineraire%20scolaire%20ligne%201505%2Carret%20scolaire%20ligne%201507%2Citineraire%20scolaire%20ligne%201507%2Carret%20scolaire%20ligne%201508%2Citineraire%20scolaire%20ligne%201508%2Carret%20scolaire%20ligne%201520%2Citineraire%20scolaire%20ligne%201520%2Carret%20scolaire%20ligne%201521%2Citineraire%20scolaire%20ligne%201521%2Carret%20scolaire%20ligne%201560%2Citineraire%20scolaire%20ligne%201560%2Carret%20scolaire%20ligne%201561%2Citineraire%20scolaire%20ligne%201561%2Carret%20scolaire%20ligne%201562%2Citineraire%20scolaire%20ligne%201562%2Carret%20scolaire%20ligne%201563%2Citineraire%20scolaire%20ligne%201563%2Carret%20scolaire%20ligne%201600%2Citineraire%20scolaire%20ligne%201600%2Carret%20scolaire%20ligne%201601%2Citineraire%20scolaire%20ligne%201601%2Carret%20scolaire%20ligne%201602%2Citineraire%20scolaire%20ligne%201602%2Carret%20scolaire%20ligne%201603%2Citineraire%20scolaire%20ligne%201603%2Carret%20scolaire%20ligne%201604%2Citineraire%20scolaire%20ligne%201604%2Carret%20scolaire%20ligne%201605%2Citineraire%20scolaire%20ligne%201605%2Carret%20scolaire%20ligne%201606%2Citineraire%20scolaire%20ligne%201606%2Carret%20scolaire%20ligne%201607%2Citineraire%20scolaire%20ligne%201607%2Carret%20scolaire%20ligne%201620%2Citineraire%20scolaire%20ligne%201620%2Carret%20scolaire%20ligne%201621%2Citineraire%20scolaire%20ligne%201621%2Carret%20scolaire%20ligne%201630%2Citineraire%20scolaire%20ligne%201630%2Carret%20scolaire%20ligne%201631%2Citineraire%20scolaire%20ligne%201631%2Carret%20scolaire%20ligne%201750%2Citineraire%20scolaire%20ligne%201750%2Carret%20scolaire%20ligne%201751%2Citineraire%20scolaire%20ligne%201751%2Carret%20scolaire%20ligne%201800%2Citineraire%20scolaire%20ligne%201800%2Carret%20scolaire%20ligne%201801%2Citineraire%20scolaire%20ligne%201801%2Carret%20scolaire%20ligne%201802%2Citineraire%20scolaire%20ligne%201802%2Carret%20scolaire%20ligne%201803%2Citineraire%20scolaire%20ligne%201803%2Carret%20scolaire%20ligne%201804%2Citineraire%20scolaire%20ligne%201804%2Carret%20scolaire%20ligne%201805%2Citineraire%20scolaire%20ligne%201805%2Carret%20scolaire%20ligne%201806%2Citineraire%20scolaire%20ligne%201806%2Carret%20scolaire%20ligne%201807%2Citineraire%20scolaire%20ligne%201807%2Carret%20scolaire%20ligne%201820%2Citineraire%20scolaire%20ligne%201820%2Carret%20scolaire%20ligne%201840%2Citineraire%20scolaire%20ligne%201840%2Carret%20scolaire%20ligne%201841%2Citineraire%20scolaire%20ligne%201841%2Carret%20scolaire%20ligne%201842%2Citineraire%20scolaire%20ligne%201842%2Carret%20scolaire%20ligne%201843%2Citineraire%20scolaire%20ligne%201843%2Carret%20scolaire%20ligne%201844%2Citineraire%20scolaire%20ligne%201844%2Carret%20scolaire%20ligne%201845%2Citineraire%20scolaire%20ligne%201845%2Carret%20scolaire%20ligne%201846%2Citineraire%20scolaire%20ligne%201846%2Carret%20scolaire%20ligne%201850%2Citineraire%20scolaire%20ligne%201850%2Carret%20scolaire%20ligne%201900%2Citineraire%20scolaire%20ligne%201900%2Carret%20scolaire%20ligne%201901%2Citineraire%20scolaire%20ligne%201901%2Carret%20scolaire%20ligne%201902%2Citineraire%20scolaire%20ligne%201902%2Carret%20scolaire%20ligne%201903%2Citineraire%20scolaire%20ligne%201903%2Carret%20scolaire%20ligne%201904%2Citineraire%20scolaire%20ligne%201904%2Carret%20scolaire%20ligne%201930%2Citineraire%20scolaire%20ligne%201930%2Carret%20scolaire%20ligne%201931%2Citineraire%20scolaire%20ligne%201931 (Réseau > Scolaire)

Problem: the user doesn't know about this problem (this is a message sent by the server, not displayed in the interface).

Solution: display a message to the final user to tell him that "too many layers have been loaded in xxx group".

Additional information or points to watch out for

GSGMF-584

[remyguillaume]

@sbrunner I think we should find a more general solution here. When any error occurs (including drawing error for example), we should display an error message.
For example, I some times get a "msDrawMap(): Image handling error. Failed to draw layer named" (http status 400) from mapserv_proxy, and in this case the layer just won't be drawn, and the user doesn't get any information. He can think that the are no data, whereas an error occurs.

Furthermore, could it be possible to use something else than the layer name in the URL ? The LayerID for example ? Or a Generated hash that identifies the layer ? Because the URL length limit can be reached relatively quickly when the layer have big long explicit names.

[remyguillaume]

If this is not too complicated, I would integrate this in 2.8, what do you think ?

[rbovard]

I like the idea to use an id instead of a possibly long layer name or layer group name.

Just be careful to not forget to handle stored permalinks with an update script (or something else).

[sbrunner]

This should add to the list of issue to be estimated for the 2.8 :-)