[OpenStreetMap] #4471: Attempt to remove all members from a relation is silently ignored

[OpenStreetMap]

#4471: Attempt to remove all members from a relation is silently ignored
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 Reporter:  woodpeck  |       Owner:  rails-dev@…                
     Type:  defect    |      Status:  new                        
 Priority:  minor     |   Milestone:                             
Component:  api       |     Version:                             
 Keywords:            |  
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 An attempt to remove all members from a relation (by uploading a new
 version with no members) results in no change - the relation will be
 updated with a new version and new user/last modification data, but it
 will still have all its members.

 Simple test case (modify object/changeset IDs accordingly):
 {{{
 <osmChange version="0.6">
   <create>
     <node id="-1" lat="45.0809152" lon="-87.6450209" changeset="zzz"
 visible="true" timestamp="2012-05-10T23:28:27Z" version="1"/>
     <relation id="-2" visible="true" timestamp="2012-05-12T23:47:18Z"
 version="1" changeset="zzz">
       <member type="node" ref="-1" role="x"/>
     </relation>
   </create>
 </osmChange>
 }}}
 later
 {{{
 <osmChange version="0.6">
   <modify>
     <relation id="xxx" visible="true" timestamp="2012-05-12T23:47:18Z"
 version="1" changeset="zzz" />
   </modify>
 </osmChange>
 }}}
 this results in
 {{{
 <diffResult version="0.6" generator="OpenStreetMap server">
   <relation old_id="xxx" new_id="xxx" new_version="2"/>
 </diffResult>
 }}}
 but the relation is unchanged!

 It is possible that the bug is related to the "unless @members"
 https://github.com/openstreetmap/openstreetmap-
 website/blob/master/app/models/relation.rb#L164 but I cannot say for sure.

 The bug can be circumvented by deleting a relation (which will clear the
 member list) and then undeleting it through a <modify>.

 Relations without members should be allowed even though their uses are
 probably niche cases.

-- 
Ticket URL: <https://trac.openstreetmap.org/ticket/4471>
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