Order and wrap expressions for CREATE INDEX statements.
| 305 | |
| 306 | |
| 307 | class IndexExpression(Func): |
| 308 | """Order and wrap expressions for CREATE INDEX statements.""" |
| 309 | |
| 310 | template = "%(expressions)s" |
| 311 | wrapper_classes = (OrderBy, Collate) |
| 312 | |
| 313 | def set_wrapper_classes(self, connection=None): |
| 314 | # Some databases (e.g. MySQL) treats COLLATE as an indexed expression. |
| 315 | if connection and connection.features.collate_as_index_expression: |
| 316 | self.wrapper_classes = tuple( |
| 317 | [ |
| 318 | wrapper_cls |
| 319 | for wrapper_cls in self.wrapper_classes |
| 320 | if wrapper_cls is not Collate |
| 321 | ] |
| 322 | ) |
| 323 | |
| 324 | @classmethod |
| 325 | def register_wrappers(cls, *wrapper_classes): |
| 326 | cls.wrapper_classes = wrapper_classes |
| 327 | |
| 328 | def resolve_expression( |
| 329 | self, |
| 330 | query=None, |
| 331 | allow_joins=True, |
| 332 | reuse=None, |
| 333 | summarize=False, |
| 334 | for_save=False, |
| 335 | ): |
| 336 | expressions = list(self.flatten()) |
| 337 | # Split expressions and wrappers. |
| 338 | index_expressions, wrappers = partition( |
| 339 | lambda e: isinstance(e, self.wrapper_classes), |
| 340 | expressions, |
| 341 | ) |
| 342 | wrapper_types = [type(wrapper) for wrapper in wrappers] |
| 343 | if len(wrapper_types) != len(set(wrapper_types)): |
| 344 | raise ValueError( |
| 345 | "Multiple references to %s can't be used in an indexed " |
| 346 | "expression." |
| 347 | % ", ".join( |
| 348 | [wrapper_cls.__qualname__ for wrapper_cls in self.wrapper_classes] |
| 349 | ) |
| 350 | ) |
| 351 | if expressions[1 : len(wrappers) + 1] != wrappers: |
| 352 | raise ValueError( |
| 353 | "%s must be topmost expressions in an indexed expression." |
| 354 | % ", ".join( |
| 355 | [wrapper_cls.__qualname__ for wrapper_cls in self.wrapper_classes] |
| 356 | ) |
| 357 | ) |
| 358 | # Wrap expressions in parentheses if they are not column references. |
| 359 | root_expression = index_expressions[1] |
| 360 | resolve_root_expression = root_expression.resolve_expression( |
| 361 | query, |
| 362 | allow_joins, |
| 363 | reuse, |
| 364 | summarize, |
no outgoing calls