/[thuban]/branches/WIP-pyshapelib-bramz/Thuban/Model/transientdb.py

Diff of /branches/WIP-pyshapelib-bramz/Thuban/Model/transientdb.py

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-revision 844 by bh,
Tue May  6 18:05:04 2003 UTC
+revision 1002 by frank,
Thu May 22 19:41:57 2003 UTC
 Line 161 
 class TransientTableBase(table.OldTableI
          return self.column_map.has_key(col)
      def ReadRowAsDict(self, index):
+         # Implementation Strategy: Executing a completely new select
+         # statement every time this method is called is too slow. The
+         # most important usage is to read the records more or less
+         # sequentially. This happens e.g. when drawing a layer with a
+         # classification where the shapes are drawn in order of the
+         # shape ids. Another pattern is that the same row is requested
+         # several times in a row. This happens in the table view, for
+         # instance.
+         # We can exploit this to make access faster by having one cursor
+         # open all the time and keeping the last row read around in case
+         # the same row is accessed again the next time and if the row
+         # index is larger than the row we have read last we simply fetch
+         # rows from the cursor until we've reached the requested row. If
+         # the requested row index is smaller then we start a new cursor.
+         # FIXME: So far this scheme seems to work well enough. Obvious
+         # improvements would be to start the cursor at exactly the
+         # requested row (should be efficient and easy to do now that the
+         # id is the primary key) and to perhaps to also start a new
+         # cursor if the requested index is much larger than the last row
+         # so that we don't read and discard lots of the rows.
+         # Check whether we have to start a new cursor
          if self.read_record_cursor is None or index <self.read_record_last_row:
              stmt = ("SELECT %s FROM %s;"
                      % (", ".join([c.internal_name for c in self.columns]),
-Line 184 
 class TransientTableBase(table.OldTableI
+Line 208 
 class TransientTableBase(table.OldTableI
          self.read_record_last_row = index
          return dict(zip(self.orig_names, result))
+     def ReadValue(self, row, col):
+         """Return the value of the specified row and column
+         The col parameter may be the index of the column or its name.
+         """
+         # Depending on the actual access patterns of the table data, it
+         # might be a bit faster in some circumstances to not implement
+         # this via ReadRowAsDict, but this simple implementation should
+         # be fast enough for most purposes.
+         return self.ReadRowAsDict(row)[self.column_map[col].name]
      def ValueRange(self, col):
          col = self.column_map[col]
          iname = col.internal_name
-Line 245 
 class TransientTableBase(table.OldTableI
+Line 280 
 class TransientTableBase(table.OldTableI
              result.append(row[0])
          return result
+     def Dependencies(self):
+         """Placeholder for a method in a derived class.
+         Return a sequence with the tables and other data objects that
+         self depends on.
+         """
+         raise NotImplementedError
  class TransientTable(TransientTableBase):
-Line 257 
 class TransientTable(TransientTableBase)
+Line 300 
 class TransientTable(TransientTableBase)
          interface.
          """
          TransientTableBase.__init__(self, transient_db)
+         self.title = table.Title()
          self.create(table)
+     def Title(self):
+         """Return the title of the table.
+         The title is the same as that of the original table
+         """
+         return self.title
      def create(self, table):
          columns = []
          for col in table.Columns():
-Line 300 
 class TransientJoinedTable(TransientTabl
+Line 351 
 class TransientJoinedTable(TransientTabl
          Both input tables, left_table and right_table must have a
          transient_table method that returns a table object for a table
-         in the trnsient database. The join is performed on the condition
+         in the transient database. The join is performed on the condition
          that the value of the left_field column the the left table is
          equal to the value of the right_field in the right_table.
-Line 312 
 class TransientJoinedTable(TransientTabl
+Line 363 
 class TransientJoinedTable(TransientTabl
          names of the input tables without having to create prefixes.
          """
          TransientTableBase.__init__(self, transient_db)
+         self.dependencies = (left_table, right_table)
          self.left_table = left_table.transient_table()
          self.left_field = left_field
          self.right_table = right_table.transient_table()
-Line 321 
 class TransientJoinedTable(TransientTabl
+Line 373 
 class TransientJoinedTable(TransientTabl
              self.right_field = self.left_field
          self.create()
+     def Title(self):
+         """Return the title of the joined table"""
+         return "Join of %(left)s and %(right)s" \
+                % {"left": self.left_table.Title(),
+                   "right": self.right_table.Title()}
      def create(self):
          """Internal: Create the table with the joined data"""
          self.tablename = self.db.new_table_name()
-Line 353 
 class TransientJoinedTable(TransientTabl
+Line 411 
 class TransientJoinedTable(TransientTabl
                     self.orig_to_internal[self.right_field]))
          self.db.execute(stmt)
+     def Dependencies(self):
+         """Return a tuple with the two tables the join depends on."""
+         return self.dependencies
  class AutoTransientTable(table.OldTableInterfaceMixin):
-Line 367 
 class AutoTransientTable(table.OldTableI
+Line 429 
 class AutoTransientTable(table.OldTableI
          self.table = table
          self.t_table = None
+     def Title(self):
+         """Return the title of the table.
+         The title is the same as that of the original table.
+         """
+         return self.table.Title()
      def Columns(self):
          return self.table.Columns()
-Line 392 
 class AutoTransientTable(table.OldTableI
+Line 461 
 class AutoTransientTable(table.OldTableI
          else:
              return self.table.ReadRowAsDict(record)
+     def ReadValue(self, row, col):
+         """Return the value of the specified row and column
+         The col parameter may be the index of the column or its name.
+         """
+         if self.t_table is not None:
+             return self.t_table.ReadValue(row, col)
+         else:
+             return self.table.ReadValue(row, col)
      def copy_to_transient(self):
          """Internal: Create a transient table and copy the data into it"""
          self.t_table = TransientTable(self.transient_db, self)
-Line 420 
 class AutoTransientTable(table.OldTableI
+Line 499 
 class AutoTransientTable(table.OldTableI
          # Make sure to use the column object of the transient table. The
          # left argument is always a column object so we can just ask the
          # t_table for the right object.
-         return self.t_table.SimpleQuery(self.t_table.Column(left.name),
+         if hasattr(right, "name"):
-                                         comparison, right)
+             return self.t_table.SimpleQuery(self.t_table.Column(left.name),
+                                             comparison,
+                                             self.t_table.Column(right.name))
+         else:
+             return self.t_table.SimpleQuery(self.t_table.Column(left.name),
+                                             comparison, right)
+     def Dependencies(self):
+         """Return a tuple containing the original table"""
+         return (self.table,)

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