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import re
from django.db import models
from graphene.relay import PageInfo
from graphene_django.fields import DjangoConnectionField
from graphql_relay.connection.arrayconnection import cursor_to_offset, offset_to_cursor
class SimplifiedDjangoConnectionField(DjangoConnectionField):
"""A simplified extension of DjangoConnectionField
This avoids calling len() or .count() on the QuerySet which has very
poor performance on PostgresQL. The value is only used to determine if there
is another page.
This does NOT support the GraphQL args "before" or "last"
Nest Seekers does not use these anyway. If you do need to use them for some purpose,
then change just that schema field from SimplifiedDjangoConnectionField back to DjangoConnectionField
def resolve_connection(cls, connection, default_manager, args, iterable):
# iterable should be sliceable ie. a QuerySet or list
if isinstance(iterable, models.Manager):
iterable = iterable.all()
assert hasattr(iterable, "__getitem__"), ValueError(
"Iterable must support list slice {}".format(type(iterable))
connection = simplified_connection_from_list_slice(
iterable, args or {}, connection_type=connection, edge_type=connection.Edge
connection.iterable = iterable
return connection
def simplified_connection_from_list_slice(
list_slice, args=None, connection_type=None, edge_type=None, max_limit=250
Given a slice (subset) of an array, returns a connection object for use in
This function is similar to `connectionFromArray`, but is intended for use
cases where you know the cardinality of the connection, consider it too large
to materialize the entire array, and instead wish pass in a slice of the
total result large enough to cover the range specified in `args`.
assert "before" not in args, NotImplementedError(
"GraphQL query arg 'before' is not implemented in 'simplified_connection_from_list_slice'"
assert "last" not in args, NotImplementedError(
"GraphQL query arg 'last' is not implemented in 'simplified_connection_from_list_slice'"
after_cursor = args.get("after")
after = cursor_to_offset(after_cursor) if after_cursor else None
first = parse_int(args.get("first")) or max_limit
start = 0 if after is None else after + 1
end = start + first
# slice off one more than we will be returning
items = list_slice[start : end + 1]
# so we know if there is another page
has_next_page = len(items) > first
has_previous_page = start > 0
items = items[:first]
# print(
# "start: {}, end:{} length: {} prev:{} next:{}".format(
# start, end, len(items), has_previous_page, has_next_page
# )
# )
edges = [
edge_type(node=node, cursor=offset_to_cursor(start + i))
for i, node in enumerate(items)
first_edge_cursor = edges[0].cursor if edges else None
last_edge_cursor = edges[-1].cursor if edges else None
# print(
# "edges: {} first:{} last: {}".format(
# len(edges),
# cursor_to_offset(first_edge_cursor),
# cursor_to_offset(last_edge_cursor),
# )
# )
conn = connection_type(
conn.length = len(items)
return conn
# from globalapp.utils import parse_int
num_re = re.compile(r"[^0-9\.]")
def parse_int(input):
Parses a string as int
@returns {int|None}
if input is None:
return None
input = unicode(input).strip()
if len(input) > 19:
return None
clean = num_re.sub(u"", input)
if input == u'':
return None
# minus sign would get stripped off so add it back in if it was there
if input.startswith("-"):
clean = u"-%s" % clean
return int(float(clean))
except ValueError as error:
# log.warning("Failed to parse_int: '%s' ERROR: %s", input, error)
return None
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