""" Customizable serialization. """ from django.db import models from django.db.models.query import QuerySet from django.db.models.fields.related import RelatedField from django.utils.encoding import smart_unicode, is_protected_type, smart_str import decimal import inspect import types # We register serializer classes, so that we can refer to them by their # class names, if there are cyclical serialization heirachys. _serializers = {} def _field_to_tuple(field): """ Convert an item in the `fields` attribute into a 2-tuple. """ if isinstance(field, (tuple, list)): return (field[0], field[1]) return (field, None) def _fields_to_list(fields): """ Return a list of field names. """ return [_field_to_tuple(field)[0] for field in fields or ()] def _fields_to_dict(fields): """ Return a `dict` of field name -> None, or tuple of fields, or Serializer class """ return dict([_field_to_tuple(field) for field in fields or ()]) class _SkipField(Exception): """ Signals that a serialized field should be ignored. We use this mechanism as the default behavior for ensuring that we don't infinitely recurse when dealing with nested data. """ pass class _RegisterSerializer(type): """ Metaclass to register serializers. """ def __new__(cls, name, bases, attrs): # Build the class and register it. ret = super(_RegisterSerializer, cls).__new__(cls, name, bases, attrs) _serializers[name] = ret return ret class Serializer(object): """ Converts python objects into plain old native types suitable for serialization. In particular it handles models and querysets. The output format is specified by setting a number of attributes on the class. You may also override any of the serialization methods, to provide for more flexible behavior. Valid output types include anything that may be directly rendered into json, xml etc... """ __metaclass__ = _RegisterSerializer fields = () """ Specify the fields to be serialized on a model or dict. Overrides `include` and `exclude`. """ include = () """ Fields to add to the default set to be serialized on a model/dict. """ exclude = () """ Fields to remove from the default set to be serialized on a model/dict. """ rename = {} """ A dict of key->name to use for the field keys. """ related_serializer = None """ The default serializer class to use for any related models. """ depth = None """ The maximum depth to serialize to, or `None`. """ def __init__(self, depth=None, stack=[], **kwargs): if depth is not None: self.depth = depth self.stack = stack def get_fields(self, obj): """ Return the set of field names/keys to use for a model instance/dict. """ fields = self.fields # If `fields` is not set, we use the default fields and modify # them with `include` and `exclude` if not fields: default = self.get_default_fields(obj) include = self.include or () exclude = self.exclude or () fields = set(default + list(include)) - set(exclude) else: fields = _fields_to_list(self.fields) return fields def get_default_fields(self, obj): """ Return the default list of field names/keys for a model instance/dict. These are used if `fields` is not given. """ if isinstance(obj, models.Model): opts = obj._meta return [field.name for field in opts.fields + opts.many_to_many] else: return obj.keys() def get_related_serializer(self, key): info = _fields_to_dict(self.fields).get(key, None) # If an element in `fields` is a 2-tuple of (str, tuple) # then the second element of the tuple is the fields to # set on the related serializer if isinstance(info, (list, tuple)): class OnTheFlySerializer(Serializer): fields = info return OnTheFlySerializer # If an element in `fields` is a 2-tuple of (str, Serializer) # then the second element of the tuple is the Serializer # class to use for that field. elif isinstance(info, type) and issubclass(info, Serializer): return info # If an element in `fields` is a 2-tuple of (str, str) # then the second element of the tuple is the name of the Serializer # class to use for that field. # # Black magic to deal with cyclical Serializer dependancies. # Similar to what Django does for cyclically related models. elif isinstance(info, str) and info in _serializers: return _serializers[info] # Otherwise use `related_serializer` or fall back to `Serializer` return getattr(self, 'related_serializer') or Serializer def serialize_key(self, key): """ Keys serialize to their string value, unless they exist in the `rename` dict. """ return self.rename.get(smart_str(key), smart_str(key)) def serialize_val(self, key, obj): """ Convert a model field or dict value into a serializable representation. """ related_serializer = self.get_related_serializer(key) if self.depth is None: depth = None elif self.depth <= 0: return self.serialize_max_depth(obj) else: depth = self.depth - 1 if any([obj is elem for elem in self.stack]): return self.serialize_recursion(obj) else: stack = self.stack[:] stack.append(obj) return related_serializer(depth=depth, stack=stack).serialize(obj) def serialize_max_depth(self, obj): """ Determine how objects should be serialized once `depth` is exceeded. The default behavior is to ignore the field. """ raise _SkipField def serialize_recursion(self, obj): """ Determine how objects should be serialized if recursion occurs. The default behavior is to ignore the field. """ raise _SkipField def serialize_model(self, instance): """ Given a model instance or dict, serialize it to a dict.. """ data = {} fields = self.get_fields(instance) # serialize each required field for fname in fields: try: if hasattr(self, smart_str(fname)): # check first for a method 'fname' on self first meth = getattr(self, fname) if inspect.ismethod(meth) and len(inspect.getargspec(meth)[0]) == 2: obj = meth(instance) elif hasattr(instance, '__contains__') and fname in instance: # check for a key 'fname' on the instance obj = instance[fname] elif hasattr(instance, smart_str(fname)): # finally check for an attribute 'fname' on the instance obj = getattr(instance, fname) else: continue key = self.serialize_key(fname) val = self.serialize_val(fname, obj) data[key] = val except _SkipField: pass return data def serialize_iter(self, obj): """ Convert iterables into a serializable representation. """ return [self.serialize(item) for item in obj] def serialize_func(self, obj): """ Convert no-arg methods and functions into a serializable representation. """ return self.serialize(obj()) def serialize_manager(self, obj): """ Convert a model manager into a serializable representation. """ return self.serialize_iter(obj.all()) def serialize_fallback(self, obj): """ Convert any unhandled object into a serializable representation. """ return smart_unicode(obj, strings_only=True) def serialize(self, obj): """ Convert any object into a serializable representation. """ if isinstance(obj, (dict, models.Model)): # Model instances & dictionaries return self.serialize_model(obj) elif isinstance(obj, (tuple, list, set, QuerySet, types.GeneratorType)): # basic iterables return self.serialize_iter(obj) elif isinstance(obj, models.Manager): # Manager objects return self.serialize_manager(obj) elif inspect.isfunction(obj) and not inspect.getargspec(obj)[0]: # function with no args return self.serialize_func(obj) elif inspect.ismethod(obj) and len(inspect.getargspec(obj)[0]) <= 1: # bound method return self.serialize_func(obj) # Protected types are passed through as is. # (i.e. Primitives like None, numbers, dates, and Decimals.) if is_protected_type(obj): return obj # All other values are converted to string. return self.serialize_fallback(obj) 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597