| 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]), |
| 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 |
| 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) |
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