127 lines
4.7 KiB
Python
127 lines
4.7 KiB
Python
# Copyright 2010 United States Government as represented by the
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# Administrator of the National Aeronautics and Space Administration.
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# Copyright 2010-2011 OpenStack Foundation
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# Copyright 2012 Justin Santa Barbara
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# All Rights Reserved.
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#
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# Licensed under the Apache License, Version 2.0 (the "License"); you may
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# not use this file except in compliance with the License. You may obtain
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# a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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# License for the specific language governing permissions and limitations
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# under the License.
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"""Implementation of paginate query."""
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import sqlalchemy
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from cinder import exception
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from cinder.openstack.common import log as logging
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LOG = logging.getLogger(__name__)
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# copied from glance/db/sqlalchemy/api.py
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def paginate_query(query, model, limit, sort_keys, marker=None,
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sort_dir=None, sort_dirs=None):
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"""Returns a query with sorting / pagination criteria added.
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Pagination works by requiring a unique sort_key, specified by sort_keys.
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(If sort_keys is not unique, then we risk looping through values.)
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We use the last row in the previous page as the 'marker' for pagination.
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So we must return values that follow the passed marker in the order.
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With a single-valued sort_key, this would be easy: sort_key > X.
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With a compound-values sort_key, (k1, k2, k3) we must do this to repeat
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the lexicographical ordering:
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(k1 > X1) or (k1 == X1 && k2 > X2) or (k1 == X1 && k2 == X2 && k3 > X3)
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We also have to cope with different sort_directions.
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Typically, the id of the last row is used as the client-facing pagination
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marker, then the actual marker object must be fetched from the db and
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passed in to us as marker.
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:param query: the query object to which we should add paging/sorting
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:param model: the ORM model class
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:param limit: maximum number of items to return
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:param sort_keys: array of attributes by which results should be sorted
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:param marker: the last item of the previous page; we returns the next
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results after this value.
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:param sort_dir: direction in which results should be sorted (asc, desc)
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:param sort_dirs: per-column array of sort_dirs, corresponding to sort_keys
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:rtype: sqlalchemy.orm.query.Query
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:return: The query with sorting/pagination added.
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"""
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if 'id' not in sort_keys:
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# TODO(justinsb): If this ever gives a false-positive, check
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# the actual primary key, rather than assuming its id
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LOG.warn(_('Id not in sort_keys; is sort_keys unique?'))
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assert(not (sort_dir and sort_dirs))
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# Default the sort direction to ascending
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if sort_dirs is None and sort_dir is None:
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sort_dir = 'asc'
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# Ensure a per-column sort direction
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if sort_dirs is None:
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sort_dirs = [sort_dir for _sort_key in sort_keys]
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assert(len(sort_dirs) == len(sort_keys))
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# Add sorting
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for current_sort_key, current_sort_dir in zip(sort_keys, sort_dirs):
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sort_dir_func = {
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'asc': sqlalchemy.asc,
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'desc': sqlalchemy.desc,
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}[current_sort_dir]
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try:
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sort_key_attr = getattr(model, current_sort_key)
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except AttributeError:
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raise exception.InvalidInput(reason='Invalid sort key')
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query = query.order_by(sort_dir_func(sort_key_attr))
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# Add pagination
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if marker is not None:
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marker_values = []
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for sort_key in sort_keys:
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v = getattr(marker, sort_key)
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marker_values.append(v)
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# Build up an array of sort criteria as in the docstring
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criteria_list = []
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for i in xrange(0, len(sort_keys)):
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crit_attrs = []
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for j in xrange(0, i):
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model_attr = getattr(model, sort_keys[j])
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crit_attrs.append((model_attr == marker_values[j]))
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model_attr = getattr(model, sort_keys[i])
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if sort_dirs[i] == 'desc':
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crit_attrs.append((model_attr < marker_values[i]))
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elif sort_dirs[i] == 'asc':
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crit_attrs.append((model_attr > marker_values[i]))
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else:
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raise ValueError(_("Unknown sort direction, "
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"must be 'desc' or 'asc'"))
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criteria = sqlalchemy.sql.and_(*crit_attrs)
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criteria_list.append(criteria)
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f = sqlalchemy.sql.or_(*criteria_list)
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query = query.filter(f)
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if limit is not None:
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query = query.limit(limit)
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return query
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