# Copyright 2015 DataStax, Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import copy
from datetime import datetime, timedelta
import time
import six

from cassandra.cqlengine import columns, CQLEngineException, ValidationError, UnicodeMixin
from cassandra.cqlengine import connection
from cassandra.cqlengine.functions import Token, BaseQueryFunction, QueryValue
from cassandra.cqlengine.operators import (InOperator, EqualsOperator, GreaterThanOperator,
                                           GreaterThanOrEqualOperator, LessThanOperator,
                                           LessThanOrEqualOperator, BaseWhereOperator)
# import * ?
from cassandra.cqlengine.statements import (WhereClause, SelectStatement, DeleteStatement,
                                            UpdateStatement, AssignmentClause, InsertStatement,
                                            BaseCQLStatement, MapUpdateClause, MapDeleteClause,
                                            ListUpdateClause, SetUpdateClause, CounterUpdateClause,
                                            TransactionClause)


class QueryException(CQLEngineException):
    pass


class IfNotExistsWithCounterColumn(CQLEngineException):
    pass


class LWTException(CQLEngineException):
    pass


class DoesNotExist(QueryException):
    pass


class MultipleObjectsReturned(QueryException):
    pass


def check_applied(result):
    """
    check if result contains some column '[applied]' with false value,
    if that value is false, it means our light-weight transaction didn't
    applied to database.
    """
    if result and '[applied]' in result[0] and not result[0]['[applied]']:
        raise LWTException('')


class AbstractQueryableColumn(UnicodeMixin):
    """
    exposes cql query operators through pythons
    builtin comparator symbols
    """

    def _get_column(self):
        raise NotImplementedError

    def __unicode__(self):
        raise NotImplementedError

    def _to_database(self, val):
        if isinstance(val, QueryValue):
            return val
        else:
            return self._get_column().to_database(val)

    def in_(self, item):
        """
        Returns an in operator

        used where you'd typically want to use python's `in` operator
        """
        return WhereClause(six.text_type(self), InOperator(), item)

    def __eq__(self, other):
        return WhereClause(six.text_type(self), EqualsOperator(), self._to_database(other))

    def __gt__(self, other):
        return WhereClause(six.text_type(self), GreaterThanOperator(), self._to_database(other))

    def __ge__(self, other):
        return WhereClause(six.text_type(self), GreaterThanOrEqualOperator(), self._to_database(other))

    def __lt__(self, other):
        return WhereClause(six.text_type(self), LessThanOperator(), self._to_database(other))

    def __le__(self, other):
        return WhereClause(six.text_type(self), LessThanOrEqualOperator(), self._to_database(other))


class BatchType(object):
    Unlogged = 'UNLOGGED'
    Counter = 'COUNTER'


class BatchQuery(object):
    """
    Handles the batching of queries

    http://www.datastax.com/docs/1.2/cql_cli/cql/BATCH
    """
    _consistency = None

    def __init__(self, batch_type=None, timestamp=None, consistency=None, execute_on_exception=False,
                 timeout=connection.NOT_SET):
        """
        :param batch_type: (optional) One of batch type values available through BatchType enum
        :type batch_type: str or None
        :param timestamp: (optional) A datetime or timedelta object with desired timestamp to be applied
            to the batch transaction.
        :type timestamp: datetime or timedelta or None
        :param consistency: (optional) One of consistency values ("ANY", "ONE", "QUORUM" etc)
        :type consistency: The :class:`.ConsistencyLevel` to be used for the batch query, or None.
        :param execute_on_exception: (Defaults to False) Indicates that when the BatchQuery instance is used
            as a context manager the queries accumulated within the context must be executed despite
            encountering an error within the context. By default, any exception raised from within
            the context scope will cause the batched queries not to be executed.
        :type execute_on_exception: bool
        :param timeout: (optional) Timeout for the entire batch (in seconds), if not specified fallback
            to default session timeout
        :type timeout: float or None
        """
        self.queries = []
        self.batch_type = batch_type
        if timestamp is not None and not isinstance(timestamp, (datetime, timedelta)):
            raise CQLEngineException('timestamp object must be an instance of datetime')
        self.timestamp = timestamp
        self._consistency = consistency
        self._execute_on_exception = execute_on_exception
        self._timeout = timeout
        self._callbacks = []

    def add_query(self, query):
        if not isinstance(query, BaseCQLStatement):
            raise CQLEngineException('only BaseCQLStatements can be added to a batch query')
        self.queries.append(query)

    def consistency(self, consistency):
        self._consistency = consistency

    def _execute_callbacks(self):
        for callback, args, kwargs in self._callbacks:
            callback(*args, **kwargs)

        # trying to clear up the ref counts for objects mentioned in the set
        del self._callbacks

    def add_callback(self, fn, *args, **kwargs):
        """Add a function and arguments to be passed to it to be executed after the batch executes.

        A batch can support multiple callbacks.

        Note, that if the batch does not execute, the callbacks are not executed.
        A callback, thus, is an "on batch success" handler.

        :param fn: Callable object
        :type fn: callable
        :param *args: Positional arguments to be passed to the callback at the time of execution
        :param **kwargs: Named arguments to be passed to the callback at the time of execution
        """
        if not callable(fn):
            raise ValueError("Value for argument 'fn' is {0} and is not a callable object.".format(type(fn)))
        self._callbacks.append((fn, args, kwargs))

    def execute(self):
        if len(self.queries) == 0:
            # Empty batch is a no-op
            # except for callbacks
            self._execute_callbacks()
            return

        opener = 'BEGIN ' + (self.batch_type + ' ' if self.batch_type else '') + ' BATCH'
        if self.timestamp:

            if isinstance(self.timestamp, six.integer_types):
                ts = self.timestamp
            elif isinstance(self.timestamp, (datetime, timedelta)):
                ts = self.timestamp
                if isinstance(self.timestamp, timedelta):
                    ts += datetime.now()  # Apply timedelta
                ts = int(time.mktime(ts.timetuple()) * 1e+6 + ts.microsecond)
            else:
                raise ValueError("Batch expects a long, a timedelta, or a datetime")

            opener += ' USING TIMESTAMP {0}'.format(ts)

        query_list = [opener]
        parameters = {}
        ctx_counter = 0
        for query in self.queries:
            query.update_context_id(ctx_counter)
            ctx = query.get_context()
            ctx_counter += len(ctx)
            query_list.append('  ' + str(query))
            parameters.update(ctx)

        query_list.append('APPLY BATCH;')

        tmp = connection.execute('\n'.join(query_list), parameters, self._consistency, self._timeout)
        check_applied(tmp)

        self.queries = []
        self._execute_callbacks()

    def __enter__(self):
        return self

    def __exit__(self, exc_type, exc_val, exc_tb):
        # don't execute if there was an exception by default
        if exc_type is not None and not self._execute_on_exception:
            return
        self.execute()


class AbstractQuerySet(object):

    def __init__(self, model):
        super(AbstractQuerySet, self).__init__()
        self.model = model

        # Where clause filters
        self._where = []

        # Transaction clause filters
        self._transaction = []

        # ordering arguments
        self._order = []

        self._allow_filtering = False

        # CQL has a default limit of 10000, it's defined here
        # because explicit is better than implicit
        self._limit = 10000

        # see the defer and only methods
        self._defer_fields = []
        self._only_fields = []

        self._values_list = False
        self._flat_values_list = False

        # results cache
        self._result_cache = None
        self._result_idx = None

        self._batch = None
        self._ttl = getattr(model, '__default_ttl__', None)
        self._consistency = None
        self._timestamp = None
        self._if_not_exists = False
        self._timeout = connection.NOT_SET

    @property
    def column_family_name(self):
        return self.model.column_family_name()

    def _execute(self, q):
        if self._batch:
            return self._batch.add_query(q)
        else:
            result = connection.execute(q, consistency_level=self._consistency, timeout=self._timeout)
            if self._transaction:
                check_applied(result)
            return result

    def __unicode__(self):
        return six.text_type(self._select_query())

    def __str__(self):
        return str(self.__unicode__())

    def __call__(self, *args, **kwargs):
        return self.filter(*args, **kwargs)

    def __deepcopy__(self, memo):
        clone = self.__class__(self.model)
        for k, v in self.__dict__.items():
            if k in ['_con', '_cur', '_result_cache', '_result_idx']:  # don't clone these
                clone.__dict__[k] = None
            elif k == '_batch':
                # we need to keep the same batch instance across
                # all queryset clones, otherwise the batched queries
                # fly off into other batch instances which are never
                # executed, thx @dokai
                clone.__dict__[k] = self._batch
            elif k == '_timeout':
                clone.__dict__[k] = self._timeout
            else:
                clone.__dict__[k] = copy.deepcopy(v, memo)

        return clone

    def __len__(self):
        self._execute_query()
        return len(self._result_cache)

    # ----query generation / execution----

    def _select_fields(self):
        """ returns the fields to select """
        return []

    def _validate_select_where(self):
        """ put select query validation here """

    def _select_query(self):
        """
        Returns a select clause based on the given filter args
        """
        if self._where:
            self._validate_select_where()
        return SelectStatement(
            self.column_family_name,
            fields=self._select_fields(),
            where=self._where,
            order_by=self._order,
            limit=self._limit,
            allow_filtering=self._allow_filtering
        )

    # ----Reads------

    def _execute_query(self):
        if self._batch:
            raise CQLEngineException("Only inserts, updates, and deletes are available in batch mode")
        if self._result_cache is None:
            self._result_cache = list(self._execute(self._select_query()))
            self._construct_result = self._get_result_constructor()

    def _fill_result_cache_to_idx(self, idx):
        self._execute_query()
        if self._result_idx is None:
            self._result_idx = -1

        qty = idx - self._result_idx
        if qty < 1:
            return
        else:
            for idx in range(qty):
                self._result_idx += 1
                self._result_cache[self._result_idx] = self._construct_result(self._result_cache[self._result_idx])

    def __iter__(self):
        self._execute_query()

        for idx in range(len(self._result_cache)):
            instance = self._result_cache[idx]
            if isinstance(instance, dict):
                self._fill_result_cache_to_idx(idx)
            yield self._result_cache[idx]

    def __getitem__(self, s):
        self._execute_query()

        num_results = len(self._result_cache)

        if isinstance(s, slice):
            # calculate the amount of results that need to be loaded
            end = num_results if s.step is None else s.step
            if end < 0:
                end += num_results
            else:
                end -= 1
            self._fill_result_cache_to_idx(end)
            return self._result_cache[s.start:s.stop:s.step]
        else:
            # return the object at this index
            s = int(s)

            # handle negative indexing
            if s < 0:
                s += num_results

            if s >= num_results:
                raise IndexError
            else:
                self._fill_result_cache_to_idx(s)
                return self._result_cache[s]

    def _get_result_constructor(self):
        """
        Returns a function that will be used to instantiate query results
        """
        raise NotImplementedError

    def batch(self, batch_obj):
        """
        Set a batch object to run the query on.

        Note: running a select query with a batch object will raise an exception
        """
        if batch_obj is not None and not isinstance(batch_obj, BatchQuery):
            raise CQLEngineException('batch_obj must be a BatchQuery instance or None')
        clone = copy.deepcopy(self)
        clone._batch = batch_obj
        return clone

    def first(self):
        try:
            return six.next(iter(self))
        except StopIteration:
            return None

    def all(self):
        """
        Returns a queryset matching all rows

        .. code-block:: python

            for user in User.objects().all():
                print(user)
        """
        return copy.deepcopy(self)

    def consistency(self, consistency):
        """
        Sets the consistency level for the operation. See :class:`.ConsistencyLevel`.

        .. code-block:: python

            for user in User.objects(id=3).consistency(CL.ONE):
                print(user)
        """
        clone = copy.deepcopy(self)
        clone._consistency = consistency
        return clone

    def _parse_filter_arg(self, arg):
        """
        Parses a filter arg in the format:
        <colname>__<op>
        :returns: colname, op tuple
        """
        statement = arg.rsplit('__', 1)
        if len(statement) == 1:
            return arg, None
        elif len(statement) == 2:
            return statement[0], statement[1]
        else:
            raise QueryException("Can't parse '{0}'".format(arg))

    def iff(self, *args, **kwargs):
        """Adds IF statements to queryset"""
        if len([x for x in kwargs.values() if x is None]):
            raise CQLEngineException("None values on iff are not allowed")

        clone = copy.deepcopy(self)
        for operator in args:
            if not isinstance(operator, TransactionClause):
                raise QueryException('{0} is not a valid query operator'.format(operator))
            clone._transaction.append(operator)

        for col_name, val in kwargs.items():
            exists = False
            try:
                column = self.model._get_column(col_name)
            except KeyError:
                if col_name == 'pk__token':
                    if not isinstance(val, Token):
                        raise QueryException("Virtual column 'pk__token' may only be compared to Token() values")
                    column = columns._PartitionKeysToken(self.model)
                else:
                    raise QueryException("Can't resolve column name: '{0}'".format(col_name))

            if isinstance(val, Token):
                if col_name != 'pk__token':
                    raise QueryException("Token() values may only be compared to the 'pk__token' virtual column")
                partition_columns = column.partition_columns
                if len(partition_columns) != len(val.value):
                    raise QueryException(
                        'Token() received {0} arguments but model has {1} partition keys'.format(
                            len(val.value), len(partition_columns)))
                val.set_columns(partition_columns)

            if isinstance(val, BaseQueryFunction) or exists is True:
                query_val = val
            else:
                query_val = column.to_database(val)

            clone._transaction.append(TransactionClause(col_name, query_val))

        return clone

    def filter(self, *args, **kwargs):
        """
        Adds WHERE arguments to the queryset, returning a new queryset

        See :ref:`retrieving-objects-with-filters`

        Returns a QuerySet filtered on the keyword arguments
        """
        # add arguments to the where clause filters
        if len([x for x in kwargs.values() if x is None]):
            raise CQLEngineException("None values on filter are not allowed")

        clone = copy.deepcopy(self)
        for operator in args:
            if not isinstance(operator, WhereClause):
                raise QueryException('{0} is not a valid query operator'.format(operator))
            clone._where.append(operator)

        for arg, val in kwargs.items():
            col_name, col_op = self._parse_filter_arg(arg)
            quote_field = True
            # resolve column and operator
            try:
                column = self.model._get_column(col_name)
            except KeyError:
                if col_name == 'pk__token':
                    if not isinstance(val, Token):
                        raise QueryException("Virtual column 'pk__token' may only be compared to Token() values")
                    column = columns._PartitionKeysToken(self.model)
                    quote_field = False
                else:
                    raise QueryException("Can't resolve column name: '{0}'".format(col_name))

            if isinstance(val, Token):
                if col_name != 'pk__token':
                    raise QueryException("Token() values may only be compared to the 'pk__token' virtual column")
                partition_columns = column.partition_columns
                if len(partition_columns) != len(val.value):
                    raise QueryException(
                        'Token() received {0} arguments but model has {1} partition keys'.format(
                            len(val.value), len(partition_columns)))
                val.set_columns(partition_columns)

            # get query operator, or use equals if not supplied
            operator_class = BaseWhereOperator.get_operator(col_op or 'EQ')
            operator = operator_class()

            if isinstance(operator, InOperator):
                if not isinstance(val, (list, tuple)):
                    raise QueryException('IN queries must use a list/tuple value')
                query_val = [column.to_database(v) for v in val]
            elif isinstance(val, BaseQueryFunction):
                query_val = val
            else:
                query_val = column.to_database(val)

            clone._where.append(WhereClause(column.db_field_name, operator, query_val, quote_field=quote_field))

        return clone

    def get(self, *args, **kwargs):
        """
        Returns a single instance matching this query, optionally with additional filter kwargs.

        See :ref:`retrieving-objects-with-filters`

        Returns a single object matching the QuerySet.

        .. code-block:: python

            user = User.get(id=1)

        If no objects are matched, a :class:`~.DoesNotExist` exception is raised.

        If more than one object is found, a :class:`~.MultipleObjectsReturned` exception is raised.
        """
        if args or kwargs:
            return self.filter(*args, **kwargs).get()

        self._execute_query()
        if len(self._result_cache) == 0:
            raise self.model.DoesNotExist
        elif len(self._result_cache) > 1:
            raise self.model.MultipleObjectsReturned('{0} objects found'.format(len(self._result_cache)))
        else:
            return self[0]

    def _get_ordering_condition(self, colname):
        order_type = 'DESC' if colname.startswith('-') else 'ASC'
        colname = colname.replace('-', '')

        return colname, order_type

    def order_by(self, *colnames):
        """
        Sets the column(s) to be used for ordering

        Default order is ascending, prepend a '-' to any column name for descending

        *Note: column names must be a clustering key*

        .. code-block:: python

            from uuid import uuid1,uuid4

            class Comment(Model):
                photo_id = UUID(primary_key=True)
                comment_id = TimeUUID(primary_key=True, default=uuid1) # second primary key component is a clustering key
                comment = Text()

            sync_table(Comment)

            u = uuid4()
            for x in range(5):
                Comment.create(photo_id=u, comment="test %d" % x)

            print("Normal")
            for comment in Comment.objects(photo_id=u):
                print comment.comment_id

            print("Reversed")
            for comment in Comment.objects(photo_id=u).order_by("-comment_id"):
                print comment.comment_id
        """
        if len(colnames) == 0:
            clone = copy.deepcopy(self)
            clone._order = []
            return clone

        conditions = []
        for colname in colnames:
            conditions.append('"{0}" {1}'.format(*self._get_ordering_condition(colname)))

        clone = copy.deepcopy(self)
        clone._order.extend(conditions)
        return clone

    def count(self):
        """
        Returns the number of rows matched by this query
        """
        if self._batch:
            raise CQLEngineException("Only inserts, updates, and deletes are available in batch mode")

        if self._result_cache is None:
            query = self._select_query()
            query.count = True
            result = self._execute(query)
            return result[0]['count']
        else:
            return len(self._result_cache)

    def limit(self, v):
        """
        Limits the number of results returned by Cassandra.

        *Note that CQL's default limit is 10,000, so all queries without a limit set explicitly will have an implicit limit of 10,000*

        .. code-block:: python

            for user in User.objects().limit(100):
                print(user)
        """
        if not (v is None or isinstance(v, six.integer_types)):
            raise TypeError
        if v == self._limit:
            return self

        if v < 0:
            raise QueryException("Negative limit is not allowed")

        clone = copy.deepcopy(self)
        clone._limit = v
        return clone

    def allow_filtering(self):
        """
        Enables the (usually) unwise practive of querying on a clustering key without also defining a partition key
        """
        clone = copy.deepcopy(self)
        clone._allow_filtering = True
        return clone

    def _only_or_defer(self, action, fields):
        clone = copy.deepcopy(self)
        if clone._defer_fields or clone._only_fields:
            raise QueryException("QuerySet alread has only or defer fields defined")

        # check for strange fields
        missing_fields = [f for f in fields if f not in self.model._columns.keys()]
        if missing_fields:
            raise QueryException(
                "Can't resolve fields {0} in {1}".format(
                    ', '.join(missing_fields), self.model.__name__))

        if action == 'defer':
            clone._defer_fields = fields
        elif action == 'only':
            clone._only_fields = fields
        else:
            raise ValueError

        return clone

    def only(self, fields):
        """ Load only these fields for the returned query """
        return self._only_or_defer('only', fields)

    def defer(self, fields):
        """ Don't load these fields for the returned query """
        return self._only_or_defer('defer', fields)

    def create(self, **kwargs):
        return self.model(**kwargs).batch(self._batch).ttl(self._ttl).\
            consistency(self._consistency).if_not_exists(self._if_not_exists).\
            timestamp(self._timestamp).save()

    def delete(self):
        """
        Deletes the contents of a query
        """
        # validate where clause
        partition_key = [x for x in self.model._primary_keys.values()][0]
        if not any([c.field == partition_key.column_name for c in self._where]):
            raise QueryException("The partition key must be defined on delete queries")

        dq = DeleteStatement(
            self.column_family_name,
            where=self._where,
            timestamp=self._timestamp
        )
        self._execute(dq)

    def __eq__(self, q):
        if len(self._where) == len(q._where):
            return all([w in q._where for w in self._where])
        return False

    def __ne__(self, q):
        return not (self != q)

    def timeout(self, timeout):
        """
        :param timeout: Timeout for the query (in seconds)
        :type timeout: float or None
        """
        clone = copy.deepcopy(self)
        clone._timeout = timeout
        return clone


class ResultObject(dict):
    """
    adds attribute access to a dictionary
    """

    def __getattr__(self, item):
        try:
            return self[item]
        except KeyError:
            raise AttributeError


class SimpleQuerySet(AbstractQuerySet):
    """

    """

    def _get_result_constructor(self):
        """
        Returns a function that will be used to instantiate query results
        """
        def _construct_instance(values):
            return ResultObject(values)
        return _construct_instance


class ModelQuerySet(AbstractQuerySet):
    """
    """
    def _validate_select_where(self):
        """ Checks that a filterset will not create invalid select statement """
        # check that there's either a = or IN relationship with a primary key or indexed field
        equal_ops = [self.model._columns.get(w.field) for w in self._where if isinstance(w.operator, EqualsOperator)]
        token_comparison = any([w for w in self._where if isinstance(w.value, Token)])
        if not any([w.primary_key or w.index for w in equal_ops]) and not token_comparison and not self._allow_filtering:
            raise QueryException('Where clauses require either a "=" or "IN" comparison with either a primary key or indexed field')

        if not self._allow_filtering:
            # if the query is not on an indexed field
            if not any([w.index for w in equal_ops]):
                if not any([w.partition_key for w in equal_ops]) and not token_comparison:
                    raise QueryException('Filtering on a clustering key without a partition key is not allowed unless allow_filtering() is called on the querset')

    def _select_fields(self):
        if self._defer_fields or self._only_fields:
            fields = self.model._columns.keys()
            if self._defer_fields:
                fields = [f for f in fields if f not in self._defer_fields]
            elif self._only_fields:
                fields = self._only_fields
            return [self.model._columns[f].db_field_name for f in fields]
        return super(ModelQuerySet, self)._select_fields()

    def _get_result_constructor(self):
        """ Returns a function that will be used to instantiate query results """
        if not self._values_list:  # we want models
            return lambda rows: self.model._construct_instance(rows)
        elif self._flat_values_list:  # the user has requested flattened list (1 value per row)
            return lambda row: row.popitem()[1]
        else:
            return lambda row: self._get_row_value_list(self._only_fields, row)

    def _get_row_value_list(self, fields, row):
        result = []
        for x in fields:
            result.append(row[x])
        return result

    def _get_ordering_condition(self, colname):
        colname, order_type = super(ModelQuerySet, self)._get_ordering_condition(colname)

        column = self.model._columns.get(colname)
        if column is None:
            raise QueryException("Can't resolve the column name: '{0}'".format(colname))

        # validate the column selection
        if not column.primary_key:
            raise QueryException(
                "Can't order on '{0}', can only order on (clustered) primary keys".format(colname))

        pks = [v for k, v in self.model._columns.items() if v.primary_key]
        if column == pks[0]:
            raise QueryException(
                "Can't order by the first primary key (partition key), clustering (secondary) keys only")

        return column.db_field_name, order_type

    def values_list(self, *fields, **kwargs):
        """ Instructs the query set to return tuples, not model instance """
        flat = kwargs.pop('flat', False)
        if kwargs:
            raise TypeError('Unexpected keyword arguments to values_list: %s'
                            % (kwargs.keys(),))
        if flat and len(fields) > 1:
            raise TypeError("'flat' is not valid when values_list is called with more than one field.")
        clone = self.only(fields)
        clone._values_list = True
        clone._flat_values_list = flat
        return clone

    def ttl(self, ttl):
        """
        Sets the ttl (in seconds) for modified data.

        *Note that running a select query with a ttl value will raise an exception*
        """
        clone = copy.deepcopy(self)
        clone._ttl = ttl
        return clone

    def timestamp(self, timestamp):
        """
        Allows for custom timestamps to be saved with the record.
        """
        clone = copy.deepcopy(self)
        clone._timestamp = timestamp
        return clone

    def if_not_exists(self):
        if self.model._has_counter:
            raise IfNotExistsWithCounterColumn('if_not_exists cannot be used with tables containing columns')
        clone = copy.deepcopy(self)
        clone._if_not_exists = True
        return clone

    def update(self, **values):
        """
        Performs an update on the row selected by the queryset. Include values to update in the
        update like so:

        .. code-block:: python

            Model.objects(key=n).update(value='x')

        Passing in updates for columns which are not part of the model will raise a ValidationError.

        Per column validation will be performed, but instance level validation will not
        (i.e., `Model.validate` is not called).  This is sometimes referred to as a blind update.

        For example:

        .. code-block:: python

            class User(Model):
                id = Integer(primary_key=True)
                name = Text()

            setup(["localhost"], "test")
            sync_table(User)

            u = User.create(id=1, name="jon")

            User.objects(id=1).update(name="Steve")

            # sets name to null
            User.objects(id=1).update(name=None)


        Also supported is blindly adding and removing elements from container columns,
        without loading a model instance from Cassandra.

        Using the syntax `.update(column_name={x, y, z})` will overwrite the contents of the container, like updating a
        non container column. However, adding `__<operation>` to the end of the keyword arg, makes the update call add
        or remove items from the collection, without overwriting then entire column.

        Given the model below, here are the operations that can be performed on the different container columns:

        .. code-block:: python

            class Row(Model):
                row_id      = columns.Integer(primary_key=True)
                set_column  = columns.Set(Integer)
                list_column = columns.List(Integer)
                map_column  = columns.Map(Integer, Integer)

        :class:`~cqlengine.columns.Set`

        - `add`: adds the elements of the given set to the column
        - `remove`: removes the elements of the given set to the column


        .. code-block:: python

            # add elements to a set
            Row.objects(row_id=5).update(set_column__add={6})

            # remove elements to a set
            Row.objects(row_id=5).update(set_column__remove={4})

        :class:`~cqlengine.columns.List`

        - `append`: appends the elements of the given list to the end of the column
        - `prepend`: prepends the elements of the given list to the beginning of the column

        .. code-block:: python

            # append items to a list
            Row.objects(row_id=5).update(list_column__append=[6, 7])

            # prepend items to a list
            Row.objects(row_id=5).update(list_column__prepend=[1, 2])


        :class:`~cqlengine.columns.Map`

        - `update`: adds the given keys/values to the columns, creating new entries if they didn't exist, and overwriting old ones if they did

        .. code-block:: python

            # add items to a map
            Row.objects(row_id=5).update(map_column__update={1: 2, 3: 4})
        """
        if not values:
            return

        nulled_columns = set()
        us = UpdateStatement(self.column_family_name, where=self._where, ttl=self._ttl,
                             timestamp=self._timestamp, transactions=self._transaction)
        for name, val in values.items():
            col_name, col_op = self._parse_filter_arg(name)
            col = self.model._columns.get(col_name)
            # check for nonexistant columns
            if col is None:
                raise ValidationError("{0}.{1} has no column named: {2}".format(self.__module__, self.model.__name__, col_name))
            # check for primary key update attempts
            if col.is_primary_key:
                raise ValidationError("Cannot apply update to primary key '{0}' for {1}.{2}".format(col_name, self.__module__, self.model.__name__))

            # we should not provide default values in this use case.
            val = col.validate(val)

            if val is None:
                nulled_columns.add(col_name)
                continue

            # add the update statements
            if isinstance(col, columns.Counter):
                # TODO: implement counter updates
                raise NotImplementedError
            elif isinstance(col, (columns.List, columns.Set, columns.Map)):
                if isinstance(col, columns.List):
                    klass = ListUpdateClause
                elif isinstance(col, columns.Set):
                    klass = SetUpdateClause
                elif isinstance(col, columns.Map):
                    klass = MapUpdateClause
                else:
                    raise RuntimeError
                us.add_assignment_clause(klass(col_name, col.to_database(val), operation=col_op))
            else:
                us.add_assignment_clause(AssignmentClause(
                    col_name, col.to_database(val)))

        if us.assignments:
            self._execute(us)

        if nulled_columns:
            ds = DeleteStatement(self.column_family_name, fields=nulled_columns, where=self._where)
            self._execute(ds)


class DMLQuery(object):
    """
    A query object used for queries performing inserts, updates, or deletes

    this is usually instantiated by the model instance to be modified

    unlike the read query object, this is mutable
    """
    _ttl = None
    _consistency = None
    _timestamp = None
    _if_not_exists = False

    def __init__(self, model, instance=None, batch=None, ttl=None, consistency=None, timestamp=None,
                 if_not_exists=False, transaction=None, timeout=connection.NOT_SET):
        self.model = model
        self.column_family_name = self.model.column_family_name()
        self.instance = instance
        self._batch = batch
        self._ttl = ttl
        self._consistency = consistency
        self._timestamp = timestamp
        self._if_not_exists = if_not_exists
        self._transaction = transaction
        self._timeout = timeout

    def _execute(self, q):
        if self._batch:
            return self._batch.add_query(q)
        else:
            tmp = connection.execute(q, consistency_level=self._consistency, timeout=self._timeout)
            if self._if_not_exists or self._transaction:
                check_applied(tmp)
            return tmp

    def batch(self, batch_obj):
        if batch_obj is not None and not isinstance(batch_obj, BatchQuery):
            raise CQLEngineException('batch_obj must be a BatchQuery instance or None')
        self._batch = batch_obj
        return self

    def _delete_null_columns(self):
        """
        executes a delete query to remove columns that have changed to null
        """
        ds = DeleteStatement(self.column_family_name)
        deleted_fields = False
        for _, v in self.instance._values.items():
            col = v.column
            if v.deleted:
                ds.add_field(col.db_field_name)
                deleted_fields = True
            elif isinstance(col, columns.Map):
                uc = MapDeleteClause(col.db_field_name, v.value, v.previous_value)
                if uc.get_context_size() > 0:
                    ds.add_field(uc)
                    deleted_fields = True

        if deleted_fields:
            for name, col in self.model._primary_keys.items():
                ds.add_where_clause(WhereClause(
                    col.db_field_name,
                    EqualsOperator(),
                    col.to_database(getattr(self.instance, name))
                ))
            self._execute(ds)

    def update(self):
        """
        updates a row.
        This is a blind update call.
        All validation and cleaning needs to happen
        prior to calling this.
        """
        if self.instance is None:
            raise CQLEngineException("DML Query intance attribute is None")
        assert type(self.instance) == self.model
        null_clustering_key = False if len(self.instance._clustering_keys) == 0 else True
        static_changed_only = True
        statement = UpdateStatement(self.column_family_name, ttl=self._ttl,
                                    timestamp=self._timestamp, transactions=self._transaction)
        for name, col in self.instance._clustering_keys.items():
            null_clustering_key = null_clustering_key and col._val_is_null(getattr(self.instance, name, None))
        # get defined fields and their column names
        for name, col in self.model._columns.items():
            # if clustering key is null, don't include non static columns
            if null_clustering_key and not col.static and not col.partition_key:
                continue
            if not col.is_primary_key:
                val = getattr(self.instance, name, None)
                val_mgr = self.instance._values[name]

                # don't update something that is null
                if val is None:
                    continue

                # don't update something if it hasn't changed
                if not val_mgr.changed and not isinstance(col, columns.Counter):
                    continue

                static_changed_only = static_changed_only and col.static
                if isinstance(col, (columns.BaseContainerColumn, columns.Counter)):
                    # get appropriate clause
                    if isinstance(col, columns.List):
                        klass = ListUpdateClause
                    elif isinstance(col, columns.Map):
                        klass = MapUpdateClause
                    elif isinstance(col, columns.Set):
                        klass = SetUpdateClause
                    elif isinstance(col, columns.Counter):
                        klass = CounterUpdateClause
                    else:
                        raise RuntimeError

                    # do the stuff
                    clause = klass(col.db_field_name, val,
                                   previous=val_mgr.previous_value, column=col)
                    if clause.get_context_size() > 0:
                        statement.add_assignment_clause(clause)
                else:
                    statement.add_assignment_clause(AssignmentClause(
                        col.db_field_name,
                        col.to_database(val)
                    ))

        if statement.get_context_size() > 0 or self.instance._has_counter:
            for name, col in self.model._primary_keys.items():
                # only include clustering key if clustering key is not null, and non static columns are changed to avoid cql error
                if (null_clustering_key or static_changed_only) and (not col.partition_key):
                    continue
                statement.add_where_clause(WhereClause(
                    col.db_field_name,
                    EqualsOperator(),
                    col.to_database(getattr(self.instance, name))
                ))
            self._execute(statement)

        if not null_clustering_key:
            self._delete_null_columns()

    def save(self):
        """
        Creates / updates a row.
        This is a blind insert call.
        All validation and cleaning needs to happen
        prior to calling this.
        """
        if self.instance is None:
            raise CQLEngineException("DML Query intance attribute is None")
        assert type(self.instance) == self.model

        nulled_fields = set()
        if self.instance._has_counter or self.instance._can_update():
            return self.update()
        else:
            insert = InsertStatement(self.column_family_name, ttl=self._ttl, timestamp=self._timestamp, if_not_exists=self._if_not_exists)
            static_save_only = False if len(self.instance._clustering_keys) == 0 else True
            for name, col in self.instance._clustering_keys.items():
                static_save_only = static_save_only and col._val_is_null(getattr(self.instance, name, None))
            for name, col in self.instance._columns.items():
                if static_save_only and not col.static and not col.partition_key:
                    continue
                val = getattr(self.instance, name, None)
                if col._val_is_null(val):
                    if self.instance._values[name].changed:
                        nulled_fields.add(col.db_field_name)
                    continue
                insert.add_assignment_clause(AssignmentClause(
                    col.db_field_name,
                    col.to_database(getattr(self.instance, name, None))
                ))

        # skip query execution if it's empty
        # caused by pointless update queries
        if not insert.is_empty:
            self._execute(insert)
        # delete any nulled columns
        if not static_save_only:
            self._delete_null_columns()

    def delete(self):
        """ Deletes one instance """
        if self.instance is None:
            raise CQLEngineException("DML Query instance attribute is None")

        ds = DeleteStatement(self.column_family_name, timestamp=self._timestamp)
        for name, col in self.model._primary_keys.items():
            if (not col.partition_key) and (getattr(self.instance, name) is None):
                continue

            ds.add_where_clause(WhereClause(
                col.db_field_name,
                EqualsOperator(),
                col.to_database(getattr(self.instance, name))
            ))
        self._execute(ds)