from django.db import models from django.db.models.loading import BaseAppCache from django.db.models.options import DEFAULT_NAMES from django.utils import six from django.utils.module_loading import import_by_path class InvalidBasesError(ValueError): pass class ProjectState(object): """ Represents the entire project's overall state. This is the item that is passed around - we do it here rather than at the app level so that cross-app FKs/etc. resolve properly. """ def __init__(self, models=None): self.models = models or {} self.app_cache = None def add_model_state(self, model_state): self.models[(model_state.app_label, model_state.name.lower())] = model_state def clone(self): "Returns an exact copy of this ProjectState" return ProjectState( models=dict((k, v.clone()) for k, v in self.models.items()) ) def render(self): "Turns the project state into actual models in a new AppCache" if self.app_cache is None: self.app_cache = BaseAppCache() # We keep trying to render the models in a loop, ignoring invalid # base errors, until the size of the unrendered models doesn't # decrease by at least one, meaning there's a base dependency loop/ # missing base. unrendered_models = list(self.models.values()) while unrendered_models: new_unrendered_models = [] for model in unrendered_models: try: model.render(self.app_cache) except InvalidBasesError: new_unrendered_models.append(model) if len(new_unrendered_models) == len(unrendered_models): raise InvalidBasesError("Cannot resolve bases for %r" % new_unrendered_models) unrendered_models = new_unrendered_models return self.app_cache @classmethod def from_app_cache(cls, app_cache): "Takes in an AppCache and returns a ProjectState matching it" app_models = {} for model in app_cache.get_models(): model_state = ModelState.from_model(model) app_models[(model_state.app_label, model_state.name.lower())] = model_state return cls(app_models) def __eq__(self, other): if set(self.models.keys()) != set(other.models.keys()): return False return all(model == other.models[key] for key, model in self.models.items()) def __ne__(self, other): return not (self == other) class ModelState(object): """ Represents a Django Model. We don't use the actual Model class as it's not designed to have its options changed - instead, we mutate this one and then render it into a Model as required. Note that while you are allowed to mutate .fields, you are not allowed to mutate the Field instances inside there themselves - you must instead assign new ones, as these are not detached during a clone. """ def __init__(self, app_label, name, fields, options=None, bases=None): self.app_label = app_label self.name = name self.fields = fields self.options = options or {} self.bases = bases or (models.Model, ) # Sanity-check that fields is NOT a dict. It must be ordered. if isinstance(self.fields, dict): raise ValueError("ModelState.fields cannot be a dict - it must be a list of 2-tuples.") @classmethod def from_model(cls, model): """ Feed me a model, get a ModelState representing it out. """ # Deconstruct the fields fields = [] for field in model._meta.local_fields: name, path, args, kwargs = field.deconstruct() field_class = import_by_path(path) fields.append((name, field_class(*args, **kwargs))) for field in model._meta.local_many_to_many: name, path, args, kwargs = field.deconstruct() field_class = import_by_path(path) fields.append((name, field_class(*args, **kwargs))) # Extract the options options = {} for name in DEFAULT_NAMES: # Ignore some special options if name in ["app_cache", "app_label"]: continue elif name in model._meta.original_attrs: if name == "unique_together": options[name] = set(model._meta.original_attrs["unique_together"]) else: options[name] = model._meta.original_attrs[name] # Make our record bases = tuple( ("%s.%s" % (base._meta.app_label, base._meta.object_name.lower()) if hasattr(base, "_meta") else base) for base in model.__bases__ if (not hasattr(base, "_meta") or not base._meta.abstract) ) if not bases: bases = (models.Model, ) return cls( model._meta.app_label, model._meta.object_name, fields, options, bases, ) def clone(self): "Returns an exact copy of this ModelState" # We deep-clone the fields using deconstruction fields = [] for name, field in self.fields: _, path, args, kwargs = field.deconstruct() field_class = import_by_path(path) fields.append((name, field_class(*args, **kwargs))) # Now make a copy return self.__class__( app_label=self.app_label, name=self.name, fields=fields, options=dict(self.options), bases=self.bases, ) def render(self, app_cache): "Creates a Model object from our current state into the given app_cache" # First, make a Meta object meta_contents = {'app_label': self.app_label, "app_cache": app_cache} meta_contents.update(self.options) if "unique_together" in meta_contents: meta_contents["unique_together"] = list(meta_contents["unique_together"]) meta = type("Meta", tuple(), meta_contents) # Then, work out our bases bases = tuple( (app_cache.get_model(*base.split(".", 1)) if isinstance(base, six.string_types) else base) for base in self.bases ) if None in bases: raise InvalidBasesError("Cannot resolve one or more bases from %r" % self.bases) # Turn fields into a dict for the body, add other bits body = dict(self.fields) body['Meta'] = meta body['__module__'] = "__fake__" # Then, make a Model object return type( self.name, bases, body, ) def get_field_by_name(self, name): for fname, field in self.fields: if fname == name: return field raise ValueError("No field called %s on model %s" % (name, self.name)) def __eq__(self, other): return ( (self.app_label == other.app_label) and (self.name == other.name) and (len(self.fields) == len(other.fields)) and all((k1 == k2 and (f1.deconstruct()[1:] == f2.deconstruct()[1:])) for (k1, f1), (k2, f2) in zip(self.fields, other.fields)) and (self.options == other.options) and (self.bases == other.bases) ) def __ne__(self, other): return not (self == other)