/[thuban]/branches/WIP-pyshapelib-bramz/Thuban/Model/transientdb.py
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revision 841 by bh, Tue May 6 17:12:53 2003 UTC revision 849 by bh, Wed May 7 11:55:31 2003 UTC
# Line 161  class TransientTableBase(table.OldTableI Line 161  class TransientTableBase(table.OldTableI
161          return self.column_map.has_key(col)          return self.column_map.has_key(col)
162    
163      def ReadRowAsDict(self, index):      def ReadRowAsDict(self, index):
164            # Implementation Strategy: Executing a completely new select
165            # statement every time this method is called is too slow. The
166            # most important usage is to read the records more or less
167            # sequentially. This happens e.g. when drawing a layer with a
168            # classification where the shapes are drawn in order of the
169            # shape ids. Another pattern is that the same row is requested
170            # several times in a row. This happens in the table view, for
171            # instance.
172    
173            # We can exploit this to make access faster by having one cursor
174            # open all the time and keeping the last row read around in case
175            # the same row is accessed again the next time and if the row
176            # index is larger than the row we have read last we simply fetch
177            # rows from the cursor until we've reached the requested row. If
178            # the requested row index is smaller then we start a new cursor.
179    
180            # FIXME: So far this scheme seems to work well enough. Obvious
181            # improvements would be to start the cursor at exactly the
182            # requested row (should be efficient and easy to do now that the
183            # id is the primary key) and to perhaps to also start a new
184            # cursor if the requested index is much larger than the last row
185            # so that we don't read and discard lots of the rows.
186    
187            # Check whether we have to start a new cursor
188          if self.read_record_cursor is None or index <self.read_record_last_row:          if self.read_record_cursor is None or index <self.read_record_last_row:
189              stmt = ("SELECT %s FROM %s;"              stmt = ("SELECT %s FROM %s;"
190                      % (", ".join([c.internal_name for c in self.columns]),                      % (", ".join([c.internal_name for c in self.columns]),
# Line 184  class TransientTableBase(table.OldTableI Line 208  class TransientTableBase(table.OldTableI
208          self.read_record_last_row = index          self.read_record_last_row = index
209          return dict(zip(self.orig_names, result))          return dict(zip(self.orig_names, result))
210    
211        def ReadValue(self, row, col):
212            """Return the value of the specified row and column
213    
214            The col parameter may be the index of the column or its name.
215            """
216            # Depending on the actual access patterns of the table data, it
217            # might be a bit faster in some circumstances to not implement
218            # this via ReadRowAsDict, but this simple implementation should
219            # be fast enough for most purposes.
220            return self.ReadRowAsDict(row)[self.column_map[col].name]
221    
222      def ValueRange(self, col):      def ValueRange(self, col):
223          col = self.column_map[col]          col = self.column_map[col]
224          iname = col.internal_name          iname = col.internal_name
# Line 392  class AutoTransientTable(table.OldTableI Line 427  class AutoTransientTable(table.OldTableI
427          else:          else:
428              return self.table.ReadRowAsDict(record)              return self.table.ReadRowAsDict(record)
429    
430        def ReadValue(self, row, col):
431            """Return the value of the specified row and column
432    
433            The col parameter may be the index of the column or its name.
434            """
435            if self.t_table is not None:
436                return self.t_table.ReadValue(row, col)
437            else:
438                return self.table.ReadValue(row, col)
439    
440      def copy_to_transient(self):      def copy_to_transient(self):
441          """Internal: Create a transient table and copy the data into it"""          """Internal: Create a transient table and copy the data into it"""
442          self.t_table = TransientTable(self.transient_db, self)          self.t_table = TransientTable(self.transient_db, self)
# Line 413  class AutoTransientTable(table.OldTableI Line 458  class AutoTransientTable(table.OldTableI
458          if self.t_table is None:          if self.t_table is None:
459              self.copy_to_transient()              self.copy_to_transient()
460          return self.t_table.UniqueValues(col)          return self.t_table.UniqueValues(col)
461    
462        def SimpleQuery(self, left, comparison, right):
463            if self.t_table is None:
464                self.copy_to_transient()
465            # Make sure to use the column object of the transient table. The
466            # left argument is always a column object so we can just ask the
467            # t_table for the right object.
468            return self.t_table.SimpleQuery(self.t_table.Column(left.name),
469                                            comparison, right)
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