/[thuban]/branches/WIP-pyshapelib-bramz/Thuban/Model/transientdb.py
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revision 1511 by bh, Tue Jul 29 14:48:57 2003 UTC revision 1961 by bh, Wed Nov 19 15:46:03 2003 UTC
# Line 85  class ColumnReference: Line 85  class ColumnReference:
85          self.internal_name = internal_name          self.internal_name = internal_name
86    
87    
88  class TransientTableBase(table.OldTableInterfaceMixin):  class TransientTableBase:
89    
90      """Base class for tables in the transient database"""      """Base class for tables in the transient database"""
91    
# Line 160  class TransientTableBase(table.OldTableI Line 160  class TransientTableBase(table.OldTableI
160          """          """
161          return self.column_map.has_key(col)          return self.column_map.has_key(col)
162    
163      def ReadRowAsDict(self, index):      def RowIdToOrdinal(self, gid):
164            """Return the row ordinal given its id
165    
166            At the moment the transient tables are only used for tables that
167            don't distinguish between row number and row id, so the value is
168            returned unchanged.
169            """
170            return gid
171    
172        def RowOrdinalToId(self, num):
173            """Return the rowid for given its ordinal
174    
175            At the moment the transient tables are only used for tables that
176            don't distinguish between row number and row id, so the value is
177            returned unchanged.
178            """
179            return num
180    
181        def ReadRowAsDict(self, index, row_is_ordinal = 0):
182            """Return the entire row as a dictionary with column names as keys
183    
184            The row_is_ordinal is ignored because at the moment the
185            transient tables are only used for DBF files where it doesn't
186            matter.
187            """
188          # Implementation Strategy: Executing a completely new select          # Implementation Strategy: Executing a completely new select
189          # statement every time this method is called is too slow. The          # statement every time this method is called is too slow. The
190          # most important usage is to read the records more or less          # most important usage is to read the records more or less
# Line 208  class TransientTableBase(table.OldTableI Line 232  class TransientTableBase(table.OldTableI
232          self.read_record_last_row = index          self.read_record_last_row = index
233          return dict(zip(self.orig_names, result))          return dict(zip(self.orig_names, result))
234    
235      def ReadValue(self, row, col):      def ReadValue(self, row, col, row_is_ordinal = 0):
236          """Return the value of the specified row and column          """Return the value of the specified row and column
237    
238          The col parameter may be the index of the column or its name.          The col parameter may be the index of the column or its name.
239    
240            The row_is_ordinal is ignored because at the moment the
241            transient tables are only used for DBF files where it doesn't
242            matter.
243          """          """
244          # Depending on the actual access patterns of the table data, it          # Depending on the actual access patterns of the table data, it
245          # might be a bit faster in some circumstances to not implement          # might be a bit faster in some circumstances to not implement
# Line 220  class TransientTableBase(table.OldTableI Line 248  class TransientTableBase(table.OldTableI
248          return self.ReadRowAsDict(row)[self.column_map[col].name]          return self.ReadRowAsDict(row)[self.column_map[col].name]
249    
250      def ValueRange(self, col):      def ValueRange(self, col):
251            # Performance notes:
252            #
253            # In sqlite 2.8.6 the min and max aggregate functions can use an
254            # index but only when used as the only expression in the select
255            # statement (i.e. 'select min(col), max(col) from tbl;' will not
256            # use the index but 'select min(col) from tbl;' will) so we
257            # query the minimum and maximum separately.
258            #
259            # With the separate statements we can take advantage of an index
260            # if it exists. If the index doesn't exist, creating it first
261            # and then using it in the query is slower than the queries
262            # without an index. Creating the index is only an advantage if
263            # the queries are performed multiple times. With the current use
264            # patterns where ValueRange is only used occasionally by the
265            # classification generation dialog creating the index only for
266            # this usage is not really worth it, so we don't.
267          col = self.column_map[col]          col = self.column_map[col]
268          iname = col.internal_name          iname = col.internal_name
269          min, max = self.db.execute("SELECT min(%s), max(%s) FROM %s;"          min = self.db.execute("SELECT min(%s) FROM %s;"
270                                     % (iname, iname, self.tablename))                                % (iname, self.tablename))[0]
271            max = self.db.execute("SELECT max(%s) FROM %s;"
272                                  % (iname, self.tablename))[0]
273          converter = type_converter_map[col.type]          converter = type_converter_map[col.type]
274          return (converter(min), converter(max))          return (converter(min), converter(max))
275    
276      def UniqueValues(self, col):      def UniqueValues(self, col):
277            # Performance notes:
278            #
279            # In sqlite 2.8.6 there doesn't seem to be a way to query the
280            # unique items that uses an index. I've tried
281            #
282            #   SELECT col FROM tbl GROUP BY col;
283            #
284            # and
285            #
286            #   SELECT DISTINCT col FROM tbl;
287            #
288            # and in both cases the index is not used. If the index isn't
289            # used it doesn't make sense to call self.ensure_index.
290          iname = self.column_map[col].internal_name          iname = self.column_map[col].internal_name
291          cursor = self.db.cursor()          cursor = self.db.cursor()
292          cursor.execute("SELECT %s FROM %s GROUP BY %s;"          cursor.execute("SELECT %s FROM %s GROUP BY %s;"
# Line 471  class TransientJoinedTable(TitledObject, Line 530  class TransientJoinedTable(TitledObject,
530              return "INNER"              return "INNER"
531    
532    
533  class AutoTransientTable(TitledObject, table.OldTableInterfaceMixin):  class AutoTransientTable(TitledObject):
534    
535      """Table that copies data to a transient table on demand.      """Table that copies data to a transient table on demand.
536    
# Line 502  class AutoTransientTable(TitledObject, t Line 561  class AutoTransientTable(TitledObject, t
561      def NumColumns(self):      def NumColumns(self):
562          return self.table.NumColumns()          return self.table.NumColumns()
563    
564      def ReadRowAsDict(self, record):      def RowIdToOrdinal(self, gid):
565            """Return the row ordinal given its id"""
566            if self.t_table is not None:
567                return self.t_table.RowIdToOrdinal(gid)
568            else:
569                return self.table.RowIdToOrdinal(gid)
570    
571        def RowOrdinalToId(self, num):
572            """Return the rowid for given its ordinal"""
573            if self.t_table is not None:
574                return self.t_table.RowOrdinalToId(num)
575            else:
576                return self.table.RowOrdinalToId(num)
577    
578        def ReadRowAsDict(self, record, row_is_ordinal = 0):
579          """Return the record no. record as a dict mapping field names to values          """Return the record no. record as a dict mapping field names to values
580          """          """
581          if self.t_table is not None:          if self.t_table is not None:
582              return self.t_table.ReadRowAsDict(record)              return self.t_table.ReadRowAsDict(record,
583                                                  row_is_ordinal = row_is_ordinal)
584          else:          else:
585              return self.table.ReadRowAsDict(record)              return self.table.ReadRowAsDict(record,
586                                                row_is_ordinal = row_is_ordinal)
587    
588      def ReadValue(self, row, col):      def ReadValue(self, row, col, row_is_ordinal = 0):
589          """Return the value of the specified row and column          """Return the value of the specified row and column
590    
591          The col parameter may be the index of the column or its name.          The col parameter may be the index of the column or its name.
592          """          """
593          if self.t_table is not None:          if self.t_table is not None:
594              return self.t_table.ReadValue(row, col)              return self.t_table.ReadValue(row, col,
595                                              row_is_ordinal = row_is_ordinal)
596          else:          else:
597              return self.table.ReadValue(row, col)              return self.table.ReadValue(row, col,
598                                            row_is_ordinal = row_is_ordinal)
599    
600      def copy_to_transient(self):      def copy_to_transient(self):
601          """Internal: Create a transient table and copy the data into it"""          """Internal: Create a transient table and copy the data into it"""
# Line 533  class AutoTransientTable(TitledObject, t Line 610  class AutoTransientTable(TitledObject, t
610          return self.t_table          return self.t_table
611    
612      def ValueRange(self, col):      def ValueRange(self, col):
613          if self.t_table is None:          # Performance of sqlite vs. DBF for this method:
614              self.copy_to_transient()          #
615          return self.t_table.ValueRange(col)          # If the table has been copied to the sqlite database it's
616            # faster to use it even if there is no index on that column.
617            # Otherwise it's faster to simply loop through all rows in the
618            # DBF file. Copying the data to the sqlite database can take
619            # very long for large amounts of data
620            #
621            # Of course if the table is not a DBF file the issue could be
622            # different, although copying the data into sqlite first will
623            # likely always be slower than simply querying the non-sqlite
624            # table directly. Currently only DBFfiles and memory tables are
625            # used as the underlying non-sqlite table, though.
626            if self.t_table is not None:
627                return self.t_table.ValueRange(col)
628            else:
629                return self.table.ValueRange(col)
630    
631      def UniqueValues(self, col):      def UniqueValues(self, col):
632          if self.t_table is None:          # The performance trade-offs for this method are basically the
633              self.copy_to_transient()          # same as for ValueRange except that currently there doesn't
634          return self.t_table.UniqueValues(col)          # seem to be a way to take advantage of indexes in this case in
635            # sqlite. However, but it's still faster to query the transient
636            # table if it already exists.
637            if self.t_table is not None:
638                return self.t_table.UniqueValues(col)
639            else:
640                return self.table.UniqueValues(col)
641    
642      def SimpleQuery(self, left, comparison, right):      def SimpleQuery(self, left, comparison, right):
643          if self.t_table is None:          if self.t_table is None:
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