[Nuxeo-tickets] [Nuxeo Repository] #1830: DataModel/Adapters should write only what's necessary

[Nuxeo Repository]

#1830: DataModel/Adapters should write only what's necessary
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 Reporter:  gracinet    |       Owner:  gracinet 
     Type:  defect      |      Status:  new      
 Priority:  P1          |   Milestone:  CPS 3.4.4
Component:  CPSSchemas  |     Version:  TRUNK    
 Severity:  major       |    Keywords:           
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 DataModel has the concept of '''dirty''' field: a field whose value has
 been changed and therefore must be written. In CPS <= 3.4.3, this is used
 only to avoid heavy computations, like transforms. It is necessary to
 avoid writing non-dirty fields. Use-cases:

  * Some read expressions can be used to derive data from another source (a
 parent folder, for instance). This data should not be stored if we want it
 to stay dynamically in sync with the source. write_ignore_storage is not a
 valid option when we want further the user to be able to manually update
 it
  * In MetaDirectory, if a backend is read-only, this directly avoids
 writing to said backend.
  * Overall performance issues with distant sources.

 In [50922] and followers in CPSSchemas and CPSDirectory, this was
 implemented by simply restricting what's being sent to adapters.
 Unfortunately, this is not good enough, because adapters take care of
 write expressions, and some of these might need both dirty and unchanged
 fields.
 This breaks for instance editing of user entries in some ldap setups
 because cross-sets neeed the unchanged used ids to write in groups
 directory.

 The adapters should be passed the full data and indication of what has to
 be written.

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Ticket URL: <https://svn.nuxeo.org/trac/pub/ticket/1830>
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