Re: [Sqlalchemy-users] Arbitrary Mapper with aliased select causes KeyError

[Michael Bayer]

for this example, you need to define your mapper like this: max_mapper = mapper( MaxRevision, mapper_sel, primary_key = [ mapper_sel.c.name ]) which has two things.  first of all, the primary key columns must be relative to the actual selectable which the mapper is defined from...once you map against a select statement, the underlying table is arbitrary...it could be composed of multiple tables, for example.   the other thing is that a mapped class needs a primary mapper defined first.  While you can only define one primary mapper per class (which actually is per class/per entity name), you can define any number of primary mappers against a particular table or selectable...so in this case as it seems MaxRevision is just a particular view object, theres no issue creating a primary mapper for it. On Sep 27, 2006, at 9:42 AM, Nikola Vukovljak wrote: from sqlalchemy import * eng = create_engine( "postgres://user:[EMAIL PROTECTED]:9999/test" ) meta = BoundMetaData( eng ) sesh = create_session( bind_to = eng ) eng.echo = True no_populate = True try:     tab = Table( "sqla_arbitrary", \                  meta, \                  autoload = True ) except:     tab = Table( "sqla_arbitrary", \                  meta, \                  Column( "id", Integer, primary_key = True ), \                  Column( "name", String ), \                  Column( "revision", Integer ), \                  Column( "description", String ) )     tab.create()     no_populate = False class Revision( object ):     def __init__( self, name, desc, revision ):         self.name = name         self.description = desc         self.revision = revision     def __cmp__( self, other ):         if self.name == other.name and \                self.description == other.description and \                self.revision == other.revision:             return 0         return 1 class MaxRevision( object ):     def __cmp__( self, other ):         if self.name == other.name and \            self.revision and other.revision:             return 0         return 1     def __str__( self ):         return "# Name [%s], Revision: [%d] #" % ( self.name, self.revision ) def displayResults( title, results ):     print "\n%s\n" % ( title )     for r in results:         print "%s" % ( r )     print "\n\n" # Create mapper simple_mapper = mapper( Revision, tab ) # Some data d1 = Revision( "matcher1", "My first matcher", 1 ) d2 = Revision( "matcher2", "My second matcher", 1 ) d3 = Revision( "matcher3", "My third matcher", 1 ) d4 = Revision( "matcher1", "My edited once first matcher", 2 ) d5 = Revision( "matcher1", "My editied twice first matcher", 3 ) d6 = Revision( "matcher2", "My editied one second matcher", 2 ) d7 = Revision( "matcher4", "My fourth matcher", 1 ) # Insert the data if no_populate == False:     sesh.save( d1 )     sesh.save( d2 )     sesh.save( d3 )     sesh.save( d4 )     sesh.save( d5 )     sesh.save( d6 )     sesh.save( d7 )     sesh.flush() # Create a select statement sel = select( [ tab.c.name, func.max( tab.c.revision ).label( "revision" ) ], \               group_by = [ tab.c.name ] ) results = sel.execute() displayResults( "SELECT STATEMENT", results ) # Create an arbitrary mapper mapper_sel = select( [ tab.c.name, func.max( tab.c.revision ).label( "revision" ) ], group_by = [ tab.c.name ] ).alias( "x" ) print "Mapper Select: [", mapper_sel , "]\n\n" # Read only mapper max_mapper = mapper( MaxRevision, mapper_sel, primary_key = [ tab.c["name"] ], non_primary = True ) query = sesh.query( max_mapper ) results = query.select() displayResults( "MAPPER", results )

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