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import sqlalchemy.sql as sql
import sqlalchemy.orm as orm
class SelectResultsExt(orm.MapperExtension):
"""a MapperExtension that provides SelectResults functionality for the
results of query.select_by() and query.select()"""
def select_by(self, query, *args, **params):
return SelectResults(query, query.join_by(*args, **params))
def select(self, query, arg=None, **kwargs):
if hasattr(arg, '_selectable'):
return orm.EXT_PASS
else:
return SelectResults(query, arg, ops=kwargs)
class SelectResults(object):
"""Builds a query one component at a time via separate method calls,
each call transforming the previous SelectResults instance into a new SelectResults
instance with further limiting criterion added. When interpreted
in an iterator context (such as via calling list(selectresults)), executes the query."""
def __init__(self, query, clause=None, ops={}):
"""constructs a new SelectResults using the given Query object and optional WHERE
clause. ops is an optional dictionary of bind parameter values."""
self._query = query
self._clause = clause
self._ops = {}
self._ops.update(ops)
def count(self):
"""executes the SQL count() function against the SelectResults criterion."""
return self._query.count(self._clause, **self._ops)
def _col_aggregate(self, col, func):
"""executes func() function against the given column
For performance, only use subselect if order_by attribute is set.
"""
if self._ops.get('order_by'):
s1 = sql.select([col], self._clause, **self._ops).alias('u')
return sql.select([func(s1.corresponding_column(col))]).scalar()
else:
return sql.select([func(col)], self._clause, **self._ops).scalar()
def min(self, col):
"""executes the SQL min() function against the given column"""
return self._col_aggregate(col, sql.func.min)
def max(self, col):
"""executes the SQL max() function against the given column"""
return self._col_aggregate(col, sql.func.max)
def sum(self, col):
"""executes the SQL sum() function against the given column"""
return self._col_aggregate(col, sql.func.sum)
def avg(self, col):
"""executes the SQL avg() function against the given column"""
return self._col_aggregate(col, sql.func.avg)
def clone(self):
"""creates a copy of this SelectResults."""
return SelectResults(self._query, self._clause, self._ops.copy())
def filter(self, clause):
"""applies an additional WHERE clause against the query."""
new = self.clone()
new._clause = sql.and_(self._clause, clause)
return new
def order_by(self, order_by):
"""applies an ORDER BY to the query."""
new = self.clone()
new._ops['order_by'] = order_by
return new
def limit(self, limit):
"""applies a LIMIT to the query."""
return self[:limit]
def offset(self, offset):
"""applies an OFFSET to the query."""
return self[offset:]
def list(self):
"""returns the results represented by this SelectResults as a list. this results in an execution of the underlying query."""
return list(self)
def __getitem__(self, item):
if isinstance(item, slice):
start = item.start
stop = item.stop
if (isinstance(start, int) and start < 0) or \
(isinstance(stop, int) and stop < 0):
return list(self)[item]
else:
res = self.clone()
if start is not None and stop is not None:
res._ops.update(dict(offset=self._ops.get('offset', 0)+start, limit=stop-start))
elif start is None and stop is not None:
res._ops.update(dict(limit=stop))
elif start is not None and stop is None:
res._ops.update(dict(offset=self._ops.get('offset', 0)+start))
if item.step is not None:
return list(res)[None:None:item.step]
else:
return res
else:
return list(self[item:item+1])[0]
def __iter__(self):
return iter(self._query.select_whereclause(self._clause, **self._ops))
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