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Source code for blitzdb.queryset

import abc


class QuerySet(object):

    """
    Stores information about objects returned by a database query and retrieves instances of 
    these objects if necessary.

    :param backend: The backend to use for :py:meth:filter`filtering` etc.
    :param cls: The class of the documents stored in the query set.
    """

    __metaclass__ = abc.ABCMeta

    ASCENDING = 1
    DESCENDING = -1

    def __init__(self, backend, cls):
        """
        Initializes a query set.
        """
        self.cls = cls
        self.backend = backend

    @abc.abstractmethod
    def __getitem__(self, i):
        """
        Returns a specific element from a query set.

        If i is a slice instead of an index (e.g. qs[:50]), returns a subset
        of the query results. This allows user to specify an offset and/or
        limit for the query.
        """
        raise NotImplementedError

    @abc.abstractmethod
    def delete(self):
        """
        Deletes all objects contained in this query set from the database.
        """
        raise NotImplementedError

    @abc.abstractmethod
    def sort(self, *args, **kwargs):
        """
        Sort documents in this query set based on a key and order

        :param key: the property name to sort on
        :param order: either `blitzdb.queryset.QuerySet.ASCENDING`
                      or `blitzdb.queryset.QuerySet.DESCENDING`
        :returns: this queryset
        """

    @abc.abstractmethod
    def filter(self, *args, **kwargs):
        """
        Performs a `filter` operation on all documents contained in the query set.
        See :py:meth:`blitzdb.backends.base.Backend.filter` for more
        details.
        """
        raise NotImplementedError

    @abc.abstractmethod
    def __len__(self):
        """
        Return the number of documents contained in this query set.
        """
        raise NotImplementedError

    @abc.abstractmethod
    def __ne__(self, other):
        """
        Checks if two query sets are unequal.

        :param other: The object this query set is compared to.
        """
        raise NotImplementedError

    @abc.abstractmethod
    def __eq__(self, other):
        """
        Checks if two query sets are equal. Implement this in your derived query set class.
        
        :param other: The object this query set is compared to.
        """
        raise NotImplementedError