[QGIS-trac] [Quantum GIS] #1876: PostgreSQL text fields become zero-length strings when blanked on attribute update edits from QGIS

[Quantum GIS]

#1876: PostgreSQL text fields become zero-length strings when blanked on attribute
update edits from QGIS
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   Reporter:  mwtoews                           |              Owner:  nobody       
       Type:  bug                               |             Status:  new          
   Priority:  major: does not work as expected  |          Milestone:  Version 1.2.0
  Component:  Data Provider                     |            Version:  HEAD         
   Keywords:                                    |   Platform_version:               
   Platform:  All                               |           Must_fix:  No           
Status_info:  0                                 |  
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 This bug is simple to create in QGIS 1.0.x and 1.2.x.

 Edit any PostGIS layer with several text fields:
  1. Add a geometry feature in QGIS, but leave some text fields blank when
 adding attributes; commit
  1. View database record in another client app (e.g., PgAdminIII) to
 ensure that blank fields are NULL
  1. Edit the feature attributes by adding text to a NULL field;
  1. In QGIS, edit the feature attributes, but delete the text; commit

 The text field will now have a zero length text value {{{''}}} and not a
 NULL value. I have observed zero-length strings "contaminating" my
 database, and I can source these oddities to QGIS edits from when someone
 blanks out text from fields that previously had non-zero length text.

 Strictly speaking, this is not a bug, but is in a grey-area leaning toward
 "feature". Many client apps, like MS Access and pgAdminIII, consider zero-
 length strings to be NULLs. I prefer this behaviour, since it is
 consistent to the creation of the features in QGIS when no text has been
 added to some fields these were inserted as NULLs and not zero-length
 strings.

 As a suggested solution, borrow the behaviour from pgAdminIII, whereby an
 empty field is always interpreted as NULL, and a zero-length text string
 has the literal {{{''}}} (two consecutive single apostrophes). The zero-
 length literal should still be available for columns that are text but
 cannot be NULL.

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Ticket URL: <http://trac.osgeo.org/qgis/ticket/1876>
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