Example #1
0
def Deserializer(object_list, **options):
    """
    Deserialize simple Python objects back into Django ORM instances.

    It's expected that you pass the Python objects themselves (instead of a
    stream or a string) to the constructor
    """
    db = options.pop('using', DEFAULT_DB_ALIAS)
    models.get_apps()
    for d in object_list:
        # Look up the model and starting build a dict of data for it.
        Model = _get_model(d["model"])
        data = {Model._meta.pk.attname : Model._meta.pk.to_python(d["pk"])}
        m2m_data = {}

        # Handle each field
        for (field_name, field_value) in six.iteritems(d["fields"]):
            if isinstance(field_value, str):
                field_value = smart_text(field_value, options.get("encoding", settings.DEFAULT_CHARSET), strings_only=True)

            field = Model._meta.get_field(field_name)

            # Handle M2M relations
            if field.rel and isinstance(field.rel, models.ManyToManyRel):
                if hasattr(field.rel.to._default_manager, 'get_by_natural_key'):
                    def m2m_convert(value):
                        if hasattr(value, '__iter__') and not isinstance(value, six.text_type):
                            return field.rel.to._default_manager.db_manager(db).get_by_natural_key(*value).pk
                        else:
                            return smart_text(field.rel.to._meta.pk.to_python(value))
                else:
                    m2m_convert = lambda v: smart_text(field.rel.to._meta.pk.to_python(v))
                m2m_data[field.name] = [m2m_convert(pk) for pk in field_value]

            # Handle FK fields
            elif field.rel and isinstance(field.rel, models.ManyToOneRel):
                if field_value is not None:
                    if hasattr(field.rel.to._default_manager, 'get_by_natural_key'):
                        if hasattr(field_value, '__iter__') and not isinstance(field_value, six.text_type):
                            obj = field.rel.to._default_manager.db_manager(db).get_by_natural_key(*field_value)
                            value = getattr(obj, field.rel.field_name)
                            # If this is a natural foreign key to an object that
                            # has a FK/O2O as the foreign key, use the FK value
                            if field.rel.to._meta.pk.rel:
                                value = value.pk
                        else:
                            value = field.rel.to._meta.get_field(field.rel.field_name).to_python(field_value)
                        data[field.attname] = value
                    else:
                        data[field.attname] = field.rel.to._meta.get_field(field.rel.field_name).to_python(field_value)
                else:
                    data[field.attname] = None

            # Handle all other fields
            else:
                data[field.name] = field.to_python(field_value)

        yield base.DeserializedObject(Model(**data), m2m_data)
Example #2
0
 def __init__(self, stream_or_string, **options):
     """
     Init this serializer given a stream or a string
     """
     self.options = options
     if isinstance(stream_or_string, six.string_types):
         self.stream = six.StringIO(stream_or_string)
     else:
         self.stream = stream_or_string
     # hack to make sure that the models have all been loaded before
     # deserialization starts (otherwise subclass calls to get_model()
     # and friends might fail...)
     models.get_apps()
Example #3
0
    def django_table_names(self, only_existing=False):
        """
        Returns a list of all table names that have associated Django models and
        are in INSTALLED_APPS.

        If only_existing is True, the resulting list will only include the tables
        that actually exist in the database.
        """
        from djangocg.db import models, router
        tables = set()
        for app in models.get_apps():
            for model in models.get_models(app):
                if not model._meta.managed:
                    continue
                if not router.allow_syncdb(self.connection.alias, model):
                    continue
                tables.add(model._meta.db_table)
                tables.update([f.m2m_db_table() for f in model._meta.local_many_to_many])
        tables = list(tables)
        if only_existing:
            existing_tables = self.table_names()
            tables = [
                t
                for t in tables
                if self.table_name_converter(t) in existing_tables
            ]
        return tables
Example #4
0
    def sequence_list(self):
        "Returns a list of information about all DB sequences for all models in all apps."
        from djangocg.db import models, router

        apps = models.get_apps()
        sequence_list = []

        for app in apps:
            for model in models.get_models(app):
                if not model._meta.managed:
                    continue
                if not router.allow_syncdb(self.connection.alias, model):
                    continue
                for f in model._meta.local_fields:
                    if isinstance(f, models.AutoField):
                        sequence_list.append({'table': model._meta.db_table, 'column': f.column})
                        break # Only one AutoField is allowed per model, so don't bother continuing.

                for f in model._meta.local_many_to_many:
                    # If this is an m2m using an intermediate table,
                    # we don't need to reset the sequence.
                    if f.rel.through is None:
                        sequence_list.append({'table': f.m2m_db_table(), 'column': None})

        return sequence_list
Example #5
0
def emit_post_sync_signal(created_models, verbosity, interactive, db):
    # Emit the post_sync signal for every application.
    for app in models.get_apps():
        app_name = app.__name__.split('.')[-2]
        if verbosity >= 2:
            print("Running post-sync handlers for application %s" % app_name)
        models.signals.post_syncdb.send(sender=app, app=app,
            created_models=created_models, verbosity=verbosity,
            interactive=interactive, db=db)
Example #6
0
 def installed_models(self, tables):
     "Returns a set of all models represented by the provided list of table names."
     from djangocg.db import models, router
     all_models = []
     for app in models.get_apps():
         for model in models.get_models(app):
             if router.allow_syncdb(self.connection.alias, model):
                 all_models.append(model)
     tables = list(map(self.table_name_converter, tables))
     return set([
         m for m in all_models
         if self.table_name_converter(m._meta.db_table) in tables
     ])
Example #7
0
    def build_suite(self, test_labels, extra_tests=None, **kwargs):
        suite = unittest.TestSuite()

        if test_labels:
            for label in test_labels:
                if '.' in label:
                    suite.addTest(build_test(label))
                else:
                    app = get_app(label)
                    suite.addTest(build_suite(app))
        else:
            for app in get_apps():
                suite.addTest(build_suite(app))

        if extra_tests:
            for test in extra_tests:
                suite.addTest(test)

        return reorder_suite(suite, (unittest.TestCase,))
Example #8
0
    def handle(self, *app_labels, **options):
        from djangocg.db.models import get_app, get_apps, get_model

        format = options.get('format')
        indent = options.get('indent')
        using = options.get('database')
        excludes = options.get('exclude')
        show_traceback = options.get('traceback')
        use_natural_keys = options.get('use_natural_keys')
        use_base_manager = options.get('use_base_manager')

        excluded_apps = set()
        excluded_models = set()
        for exclude in excludes:
            if '.' in exclude:
                app_label, model_name = exclude.split('.', 1)
                model_obj = get_model(app_label, model_name)
                if not model_obj:
                    raise CommandError('Unknown model in excludes: %s' % exclude)
                excluded_models.add(model_obj)
            else:
                try:
                    app_obj = get_app(exclude)
                    excluded_apps.add(app_obj)
                except ImproperlyConfigured:
                    raise CommandError('Unknown app in excludes: %s' % exclude)

        if len(app_labels) == 0:
            app_list = SortedDict((app, None) for app in get_apps() if app not in excluded_apps)
        else:
            app_list = SortedDict()
            for label in app_labels:
                try:
                    app_label, model_label = label.split('.')
                    try:
                        app = get_app(app_label)
                    except ImproperlyConfigured:
                        raise CommandError("Unknown application: %s" % app_label)
                    if app in excluded_apps:
                        continue
                    model = get_model(app_label, model_label)
                    if model is None:
                        raise CommandError("Unknown model: %s.%s" % (app_label, model_label))

                    if app in app_list.keys():
                        if app_list[app] and model not in app_list[app]:
                            app_list[app].append(model)
                    else:
                        app_list[app] = [model]
                except ValueError:
                    # This is just an app - no model qualifier
                    app_label = label
                    try:
                        app = get_app(app_label)
                    except ImproperlyConfigured:
                        raise CommandError("Unknown application: %s" % app_label)
                    if app in excluded_apps:
                        continue
                    app_list[app] = None

        # Check that the serialization format exists; this is a shortcut to
        # avoid collating all the objects and _then_ failing.
        if format not in serializers.get_public_serializer_formats():
            raise CommandError("Unknown serialization format: %s" % format)

        try:
            serializers.get_serializer(format)
        except KeyError:
            raise CommandError("Unknown serialization format: %s" % format)

        def get_objects():
            # Collate the objects to be serialized.
            for model in sort_dependencies(app_list.items()):
                if model in excluded_models:
                    continue
                if not model._meta.proxy and router.allow_syncdb(using, model):
                    if use_base_manager:
                        objects = model._base_manager
                    else:
                        objects = model._default_manager
                    for obj in objects.using(using).\
                            order_by(model._meta.pk.name).iterator():
                        yield obj

        try:
            self.stdout.ending = None
            serializers.serialize(format, get_objects(), indent=indent,
                    use_natural_keys=use_natural_keys, stream=self.stdout)
        except Exception as e:
            if show_traceback:
                raise
            raise CommandError("Unable to serialize database: %s" % e)
Example #9
0
    def handle_noargs(self, **options):

        verbosity = int(options.get("verbosity"))
        interactive = options.get("interactive")
        show_traceback = options.get("traceback")
        load_initial_data = options.get("load_initial_data")

        self.style = no_style()

        # Import the 'management' module within each installed app, to register
        # dispatcher events.
        for app_name in settings.INSTALLED_APPS:
            try:
                import_module(".management", app_name)
            except ImportError as exc:
                # This is slightly hackish. We want to ignore ImportErrors
                # if the "management" module itself is missing -- but we don't
                # want to ignore the exception if the management module exists
                # but raises an ImportError for some reason. The only way we
                # can do this is to check the text of the exception. Note that
                # we're a bit broad in how we check the text, because different
                # Python implementations may not use the same text.
                # CPython uses the text "No module named management"
                # PyPy uses "No module named myproject.myapp.management"
                msg = exc.args[0]
                if not msg.startswith("No module named") or "management" not in msg:
                    raise

        db = options.get("database")
        connection = connections[db]
        cursor = connection.cursor()

        # Get a list of already installed *models* so that references work right.
        tables = connection.introspection.table_names()
        seen_models = connection.introspection.installed_models(tables)
        created_models = set()
        pending_references = {}

        # Build the manifest of apps and models that are to be synchronized
        all_models = [
            (
                app.__name__.split(".")[-2],
                [m for m in models.get_models(app, include_auto_created=True) if router.allow_syncdb(db, m)],
            )
            for app in models.get_apps()
        ]

        def model_installed(model):
            opts = model._meta
            converter = connection.introspection.table_name_converter
            return not (
                (converter(opts.db_table) in tables)
                or (opts.auto_created and converter(opts.auto_created._meta.db_table) in tables)
            )

        manifest = SortedDict(
            (app_name, list(filter(model_installed, model_list))) for app_name, model_list in all_models
        )

        # Create the tables for each model
        if verbosity >= 1:
            self.stdout.write("Creating tables ...\n")
        for app_name, model_list in manifest.items():
            for model in model_list:
                # Create the model's database table, if it doesn't already exist.
                if verbosity >= 3:
                    self.stdout.write("Processing %s.%s model\n" % (app_name, model._meta.object_name))
                sql, references = connection.creation.sql_create_model(model, self.style, seen_models)
                seen_models.add(model)
                created_models.add(model)
                for refto, refs in references.items():
                    pending_references.setdefault(refto, []).extend(refs)
                    if refto in seen_models:
                        sql.extend(
                            connection.creation.sql_for_pending_references(refto, self.style, pending_references)
                        )
                sql.extend(connection.creation.sql_for_pending_references(model, self.style, pending_references))
                if verbosity >= 1 and sql:
                    self.stdout.write("Creating table %s\n" % model._meta.db_table)
                for statement in sql:
                    cursor.execute(statement)
                tables.append(connection.introspection.table_name_converter(model._meta.db_table))

        transaction.commit_unless_managed(using=db)

        # Send the post_syncdb signal, so individual apps can do whatever they need
        # to do at this point.
        emit_post_sync_signal(created_models, verbosity, interactive, db)

        # The connection may have been closed by a syncdb handler.
        cursor = connection.cursor()

        # Install custom SQL for the app (but only if this
        # is a model we've just created)
        if verbosity >= 1:
            self.stdout.write("Installing custom SQL ...\n")
        for app_name, model_list in manifest.items():
            for model in model_list:
                if model in created_models:
                    custom_sql = custom_sql_for_model(model, self.style, connection)
                    if custom_sql:
                        if verbosity >= 2:
                            self.stdout.write(
                                "Installing custom SQL for %s.%s model\n" % (app_name, model._meta.object_name)
                            )
                        try:
                            for sql in custom_sql:
                                cursor.execute(sql)
                        except Exception as e:
                            self.stderr.write(
                                "Failed to install custom SQL for %s.%s model: %s\n"
                                % (app_name, model._meta.object_name, e)
                            )
                            if show_traceback:
                                traceback.print_exc()
                            transaction.rollback_unless_managed(using=db)
                        else:
                            transaction.commit_unless_managed(using=db)
                    else:
                        if verbosity >= 3:
                            self.stdout.write("No custom SQL for %s.%s model\n" % (app_name, model._meta.object_name))

        if verbosity >= 1:
            self.stdout.write("Installing indexes ...\n")
        # Install SQL indices for all newly created models
        for app_name, model_list in manifest.items():
            for model in model_list:
                if model in created_models:
                    index_sql = connection.creation.sql_indexes_for_model(model, self.style)
                    if index_sql:
                        if verbosity >= 2:
                            self.stdout.write(
                                "Installing index for %s.%s model\n" % (app_name, model._meta.object_name)
                            )
                        try:
                            for sql in index_sql:
                                cursor.execute(sql)
                        except Exception as e:
                            self.stderr.write(
                                "Failed to install index for %s.%s model: %s\n" % (app_name, model._meta.object_name, e)
                            )
                            transaction.rollback_unless_managed(using=db)
                        else:
                            transaction.commit_unless_managed(using=db)

        # Load initial_data fixtures (unless that has been disabled)
        if load_initial_data:
            call_command("loaddata", "initial_data", verbosity=verbosity, database=db, skip_validation=True)
Example #10
0
def update_all_contenttypes(verbosity=2, **kwargs):
    for app in get_apps():
        update_contenttypes(app, None, verbosity, **kwargs)
Example #11
0
def validate(cls, model):
    """
    Does basic ModelAdmin option validation. Calls custom validation
    classmethod in the end if it is provided in cls. The signature of the
    custom validation classmethod should be: def validate(cls, model).
    """
    # Before we can introspect models, they need to be fully loaded so that
    # inter-relations are set up correctly. We force that here.
    models.get_apps()

    opts = model._meta
    validate_base(cls, model)

    # list_display
    if hasattr(cls, 'list_display'):
        check_isseq(cls, 'list_display', cls.list_display)
        for idx, field in enumerate(cls.list_display):
            if not callable(field):
                if not hasattr(cls, field):
                    if not hasattr(model, field):
                        try:
                            opts.get_field(field)
                        except models.FieldDoesNotExist:
                            raise ImproperlyConfigured("%s.list_display[%d], %r is not a callable or an attribute of %r or found in the model %r."
                                % (cls.__name__, idx, field, cls.__name__, model._meta.object_name))
                    else:
                        # getattr(model, field) could be an X_RelatedObjectsDescriptor
                        f = fetch_attr(cls, model, opts, "list_display[%d]" % idx, field)
                        if isinstance(f, models.ManyToManyField):
                            raise ImproperlyConfigured("'%s.list_display[%d]', '%s' is a ManyToManyField which is not supported."
                                % (cls.__name__, idx, field))

    # list_display_links
    if hasattr(cls, 'list_display_links'):
        check_isseq(cls, 'list_display_links', cls.list_display_links)
        for idx, field in enumerate(cls.list_display_links):
            if field not in cls.list_display:
                raise ImproperlyConfigured("'%s.list_display_links[%d]' "
                        "refers to '%s' which is not defined in 'list_display'."
                        % (cls.__name__, idx, field))

    # list_filter
    if hasattr(cls, 'list_filter'):
        check_isseq(cls, 'list_filter', cls.list_filter)
        for idx, item in enumerate(cls.list_filter):
            # There are three options for specifying a filter:
            #   1: 'field' - a basic field filter, possibly w/ relationships (eg, 'field__rel')
            #   2: ('field', SomeFieldListFilter) - a field-based list filter class
            #   3: SomeListFilter - a non-field list filter class
            if callable(item) and not isinstance(item, models.Field):
                # If item is option 3, it should be a ListFilter...
                if not issubclass(item, ListFilter):
                    raise ImproperlyConfigured("'%s.list_filter[%d]' is '%s'"
                            " which is not a descendant of ListFilter."
                            % (cls.__name__, idx, item.__name__))
                # ...  but not a FieldListFilter.
                if issubclass(item, FieldListFilter):
                    raise ImproperlyConfigured("'%s.list_filter[%d]' is '%s'"
                            " which is of type FieldListFilter but is not"
                            " associated with a field name."
                            % (cls.__name__, idx, item.__name__))
            else:
                if isinstance(item, (tuple, list)):
                    # item is option #2
                    field, list_filter_class = item
                    if not issubclass(list_filter_class, FieldListFilter):
                        raise ImproperlyConfigured("'%s.list_filter[%d][1]'"
                            " is '%s' which is not of type FieldListFilter."
                            % (cls.__name__, idx, list_filter_class.__name__))
                else:
                    # item is option #1
                    field = item
                # Validate the field string
                try:
                    get_fields_from_path(model, field)
                except (NotRelationField, FieldDoesNotExist):
                    raise ImproperlyConfigured("'%s.list_filter[%d]' refers to '%s'"
                            " which does not refer to a Field."
                            % (cls.__name__, idx, field))

    # list_per_page = 100
    if hasattr(cls, 'list_per_page') and not isinstance(cls.list_per_page, int):
        raise ImproperlyConfigured("'%s.list_per_page' should be a integer."
                % cls.__name__)

    # list_max_show_all
    if hasattr(cls, 'list_max_show_all') and not isinstance(cls.list_max_show_all, int):
        raise ImproperlyConfigured("'%s.list_max_show_all' should be an integer."
                % cls.__name__)

    # list_editable
    if hasattr(cls, 'list_editable') and cls.list_editable:
        check_isseq(cls, 'list_editable', cls.list_editable)
        for idx, field_name in enumerate(cls.list_editable):
            try:
                field = opts.get_field_by_name(field_name)[0]
            except models.FieldDoesNotExist:
                raise ImproperlyConfigured("'%s.list_editable[%d]' refers to a "
                    "field, '%s', not defined on %s.%s."
                    % (cls.__name__, idx, field_name, model._meta.app_label, model.__name__))
            if field_name not in cls.list_display:
                raise ImproperlyConfigured("'%s.list_editable[%d]' refers to "
                    "'%s' which is not defined in 'list_display'."
                    % (cls.__name__, idx, field_name))
            if field_name in cls.list_display_links:
                raise ImproperlyConfigured("'%s' cannot be in both '%s.list_editable'"
                    " and '%s.list_display_links'"
                    % (field_name, cls.__name__, cls.__name__))
            if not cls.list_display_links and cls.list_display[0] in cls.list_editable:
                raise ImproperlyConfigured("'%s.list_editable[%d]' refers to"
                    " the first field in list_display, '%s', which can't be"
                    " used unless list_display_links is set."
                    % (cls.__name__, idx, cls.list_display[0]))
            if not field.editable:
                raise ImproperlyConfigured("'%s.list_editable[%d]' refers to a "
                    "field, '%s', which isn't editable through the admin."
                    % (cls.__name__, idx, field_name))

    # search_fields = ()
    if hasattr(cls, 'search_fields'):
        check_isseq(cls, 'search_fields', cls.search_fields)

    # date_hierarchy = None
    if cls.date_hierarchy:
        f = get_field(cls, model, opts, 'date_hierarchy', cls.date_hierarchy)
        if not isinstance(f, (models.DateField, models.DateTimeField)):
            raise ImproperlyConfigured("'%s.date_hierarchy is "
                    "neither an instance of DateField nor DateTimeField."
                    % cls.__name__)

    # ordering = None
    if cls.ordering:
        check_isseq(cls, 'ordering', cls.ordering)
        for idx, field in enumerate(cls.ordering):
            if field == '?' and len(cls.ordering) != 1:
                raise ImproperlyConfigured("'%s.ordering' has the random "
                        "ordering marker '?', but contains other fields as "
                        "well. Please either remove '?' or the other fields."
                        % cls.__name__)
            if field == '?':
                continue
            if field.startswith('-'):
                field = field[1:]
            # Skip ordering in the format field1__field2 (FIXME: checking
            # this format would be nice, but it's a little fiddly).
            if '__' in field:
                continue
            get_field(cls, model, opts, 'ordering[%d]' % idx, field)

    if hasattr(cls, "readonly_fields"):
        check_readonly_fields(cls, model, opts)

    # list_select_related = False
    # save_as = False
    # save_on_top = False
    for attr in ('list_select_related', 'save_as', 'save_on_top'):
        if not isinstance(getattr(cls, attr), bool):
            raise ImproperlyConfigured("'%s.%s' should be a boolean."
                    % (cls.__name__, attr))


    # inlines = []
    if hasattr(cls, 'inlines'):
        check_isseq(cls, 'inlines', cls.inlines)
        for idx, inline in enumerate(cls.inlines):
            if not issubclass(inline, BaseModelAdmin):
                raise ImproperlyConfigured("'%s.inlines[%d]' does not inherit "
                        "from BaseModelAdmin." % (cls.__name__, idx))
            if not inline.model:
                raise ImproperlyConfigured("'model' is a required attribute "
                        "of '%s.inlines[%d]'." % (cls.__name__, idx))
            if not issubclass(inline.model, models.Model):
                raise ImproperlyConfigured("'%s.inlines[%d].model' does not "
                        "inherit from models.Model." % (cls.__name__, idx))
            validate_base(inline, inline.model)
            validate_inline(inline, cls, model)
Example #12
0
    def handle_noargs(self, **options):
        db = options.get('database')
        connection = connections[db]
        verbosity = int(options.get('verbosity'))
        interactive = options.get('interactive')
        # 'reset_sequences' is a stealth option
        reset_sequences = options.get('reset_sequences', True)

        self.style = no_style()

        # Import the 'management' module within each installed app, to register
        # dispatcher events.
        for app_name in settings.INSTALLED_APPS:
            try:
                import_module('.management', app_name)
            except ImportError:
                pass

        sql_list = sql_flush(self.style, connection, only_django=True, reset_sequences=reset_sequences)

        if interactive:
            confirm = input("""You have requested a flush of the database.
This will IRREVERSIBLY DESTROY all data currently in the %r database,
and return each table to the state it was in after syncdb.
Are you sure you want to do this?

    Type 'yes' to continue, or 'no' to cancel: """ % connection.settings_dict['NAME'])
        else:
            confirm = 'yes'

        if confirm == 'yes':
            try:
                cursor = connection.cursor()
                for sql in sql_list:
                    cursor.execute(sql)
            except Exception as e:
                transaction.rollback_unless_managed(using=db)
                raise CommandError("""Database %s couldn't be flushed. Possible reasons:
  * The database isn't running or isn't configured correctly.
  * At least one of the expected database tables doesn't exist.
  * The SQL was invalid.
Hint: Look at the output of 'django-admin.py sqlflush'. That's the SQL this command wasn't able to run.
The full error: %s""" % (connection.settings_dict['NAME'], e))
            transaction.commit_unless_managed(using=db)

            # Emit the post sync signal. This allows individual
            # applications to respond as if the database had been
            # sync'd from scratch.
            all_models = []
            for app in models.get_apps():
                all_models.extend([
                    m for m in models.get_models(app, include_auto_created=True)
                    if router.allow_syncdb(db, m)
                ])
            emit_post_sync_signal(set(all_models), verbosity, interactive, db)

            # Reinstall the initial_data fixture.
            kwargs = options.copy()
            kwargs['database'] = db
            if options.get('load_initial_data'):
                # Reinstall the initial_data fixture.
                call_command('loaddata', 'initial_data', **options)

        else:
            self.stdout.write("Flush cancelled.\n")
Example #13
0
    def handle(self, *fixture_labels, **options):
        using = options.get('database')

        connection = connections[using]

        if not len(fixture_labels):
            raise CommandError(
                "No database fixture specified. Please provide the path of at "
                "least one fixture in the command line."
            )

        verbosity = int(options.get('verbosity'))
        show_traceback = options.get('traceback')

        # commit is a stealth option - it isn't really useful as
        # a command line option, but it can be useful when invoking
        # loaddata from within another script.
        # If commit=True, loaddata will use its own transaction;
        # if commit=False, the data load SQL will become part of
        # the transaction in place when loaddata was invoked.
        commit = options.get('commit', True)

        # Keep a count of the installed objects and fixtures
        fixture_count = 0
        loaded_object_count = 0
        fixture_object_count = 0
        models = set()

        humanize = lambda dirname: "'%s'" % dirname if dirname else 'absolute path'

        # Get a cursor (even though we don't need one yet). This has
        # the side effect of initializing the test database (if
        # it isn't already initialized).
        cursor = connection.cursor()

        # Start transaction management. All fixtures are installed in a
        # single transaction to ensure that all references are resolved.
        if commit:
            transaction.commit_unless_managed(using=using)
            transaction.enter_transaction_management(using=using)
            transaction.managed(True, using=using)

        class SingleZipReader(zipfile.ZipFile):
            def __init__(self, *args, **kwargs):
                zipfile.ZipFile.__init__(self, *args, **kwargs)
                if settings.DEBUG:
                    assert len(self.namelist()) == 1, "Zip-compressed fixtures must contain only one file."
            def read(self):
                return zipfile.ZipFile.read(self, self.namelist()[0])

        compression_types = {
            None:   open,
            'gz':   gzip.GzipFile,
            'zip':  SingleZipReader
        }
        if has_bz2:
            compression_types['bz2'] = bz2.BZ2File

        app_module_paths = []
        for app in get_apps():
            if hasattr(app, '__path__'):
                # It's a 'models/' subpackage
                for path in app.__path__:
                    app_module_paths.append(path)
            else:
                # It's a models.py module
                app_module_paths.append(app.__file__)

        app_fixtures = [os.path.join(os.path.dirname(path), 'fixtures') for path in app_module_paths]

        try:
            with connection.constraint_checks_disabled():
                for fixture_label in fixture_labels:
                    parts = fixture_label.split('.')

                    if len(parts) > 1 and parts[-1] in compression_types:
                        compression_formats = [parts[-1]]
                        parts = parts[:-1]
                    else:
                        compression_formats = compression_types.keys()

                    if len(parts) == 1:
                        fixture_name = parts[0]
                        formats = serializers.get_public_serializer_formats()
                    else:
                        fixture_name, format = '.'.join(parts[:-1]), parts[-1]
                        if format in serializers.get_public_serializer_formats():
                            formats = [format]
                        else:
                            formats = []

                    if formats:
                        if verbosity >= 2:
                            self.stdout.write("Loading '%s' fixtures..." % fixture_name)
                    else:
                        raise CommandError(
                            "Problem installing fixture '%s': %s is not a known serialization format." %
                                (fixture_name, format))

                    if os.path.isabs(fixture_name):
                        fixture_dirs = [fixture_name]
                    else:
                        fixture_dirs = app_fixtures + list(settings.FIXTURE_DIRS) + ['']

                    for fixture_dir in fixture_dirs:
                        if verbosity >= 2:
                            self.stdout.write("Checking %s for fixtures..." % humanize(fixture_dir))

                        label_found = False
                        for combo in product([using, None], formats, compression_formats):
                            database, format, compression_format = combo
                            file_name = '.'.join(
                                p for p in [
                                    fixture_name, database, format, compression_format
                                ]
                                if p
                            )

                            if verbosity >= 3:
                                self.stdout.write("Trying %s for %s fixture '%s'..." % \
                                    (humanize(fixture_dir), file_name, fixture_name))
                            full_path = os.path.join(fixture_dir, file_name)
                            open_method = compression_types[compression_format]
                            try:
                                fixture = open_method(full_path, 'r')
                            except IOError:
                                if verbosity >= 2:
                                    self.stdout.write("No %s fixture '%s' in %s." % \
                                        (format, fixture_name, humanize(fixture_dir)))
                            else:
                                try:
                                    if label_found:
                                        raise CommandError("Multiple fixtures named '%s' in %s. Aborting." %
                                            (fixture_name, humanize(fixture_dir)))

                                    fixture_count += 1
                                    objects_in_fixture = 0
                                    loaded_objects_in_fixture = 0
                                    if verbosity >= 2:
                                        self.stdout.write("Installing %s fixture '%s' from %s." % \
                                            (format, fixture_name, humanize(fixture_dir)))

                                    objects = serializers.deserialize(format, fixture, using=using)

                                    for obj in objects:
                                        objects_in_fixture += 1
                                        if router.allow_syncdb(using, obj.object.__class__):
                                            loaded_objects_in_fixture += 1
                                            models.add(obj.object.__class__)
                                            try:
                                                obj.save(using=using)
                                            except (DatabaseError, IntegrityError) as e:
                                                e.args = ("Could not load %(app_label)s.%(object_name)s(pk=%(pk)s): %(error_msg)s" % {
                                                        'app_label': obj.object._meta.app_label,
                                                        'object_name': obj.object._meta.object_name,
                                                        'pk': obj.object.pk,
                                                        'error_msg': force_text(e)
                                                    },)
                                                raise

                                    loaded_object_count += loaded_objects_in_fixture
                                    fixture_object_count += objects_in_fixture
                                    label_found = True
                                except Exception as e:
                                    if not isinstance(e, CommandError):
                                        e.args = ("Problem installing fixture '%s': %s" % (full_path, e),)
                                    raise
                                finally:
                                    fixture.close()

                                # If the fixture we loaded contains 0 objects, assume that an
                                # error was encountered during fixture loading.
                                if objects_in_fixture == 0:
                                    raise CommandError(
                                        "No fixture data found for '%s'. (File format may be invalid.)" %
                                            (fixture_name))

            # Since we disabled constraint checks, we must manually check for
            # any invalid keys that might have been added
            table_names = [model._meta.db_table for model in models]
            try:
                connection.check_constraints(table_names=table_names)
            except Exception as e:
                e.args = ("Problem installing fixtures: %s" % e,)
                raise

        except (SystemExit, KeyboardInterrupt):
            raise
        except Exception as e:
            if commit:
                transaction.rollback(using=using)
                transaction.leave_transaction_management(using=using)
            raise

        # If we found even one object in a fixture, we need to reset the
        # database sequences.
        if loaded_object_count > 0:
            sequence_sql = connection.ops.sequence_reset_sql(no_style(), models)
            if sequence_sql:
                if verbosity >= 2:
                    self.stdout.write("Resetting sequences\n")
                for line in sequence_sql:
                    cursor.execute(line)

        if commit:
            transaction.commit(using=using)
            transaction.leave_transaction_management(using=using)

        if verbosity >= 1:
            if fixture_object_count == loaded_object_count:
                self.stdout.write("Installed %d object(s) from %d fixture(s)" % (
                    loaded_object_count, fixture_count))
            else:
                self.stdout.write("Installed %d object(s) (of %d) from %d fixture(s)" % (
                    loaded_object_count, fixture_object_count, fixture_count))

        # Close the DB connection. This is required as a workaround for an
        # edge case in MySQL: if the same connection is used to
        # create tables, load data, and query, the query can return
        # incorrect results. See Django #7572, MySQL #37735.
        if commit:
            connection.close()