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Ordering #76

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Ordering #76

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a6e6656
use CTE with ordering for postgres to avoid deadlocks
itimky Sep 21, 2018
081fcae
add "ordered" parameter to bulk_update to use CTE with ordering to av…
itimky Oct 20, 2018
9a2c6df
use string .format instead of f-strings
itimky Oct 20, 2018
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52 changes: 40 additions & 12 deletions django_bulk_update/helper.py
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Original file line number Diff line number Diff line change
Expand Up @@ -114,7 +114,8 @@ def get_fields(update_fields, exclude_fields, meta, obj=None):


def bulk_update(objs, meta=None, update_fields=None, exclude_fields=None,
using='default', batch_size=None, pk_field='pk'):
using='default', batch_size=None, pk_field='pk',
ordered=False):
assert batch_size is None or batch_size > 0

# force to retrieve objs from the DB at the beginning,
Expand Down Expand Up @@ -154,11 +155,16 @@ def bulk_update(objs, meta=None, update_fields=None, exclude_fields=None,
# Sqlite also gives some trouble with cast, at least for datetime,
# but is also permissive for uncast values
vendor = connection.vendor

use_cast = 'mysql' not in vendor and 'sqlite' not in vendor
if ordered:
template = 'CASE cte."{pk_column}" {cases}ELSE cte."{column}" END'
else:
template = 'CASE "{pk_column}" {cases}ELSE "{column}" END'
if use_cast:
template = '"{column}" = CAST(CASE "{pk_column}" {cases}ELSE "{column}" END AS {type})'
template = '"{column}" = CAST(' + template + ' AS {type})'
else:
template = '"{column}" = (CASE "{pk_column}" {cases}ELSE "{column}" END)'
template = '"{column}" = (' + template + ')'

case_template = "WHEN %s THEN {} "

Expand Down Expand Up @@ -191,11 +197,7 @@ def bulk_update(objs, meta=None, update_fields=None, exclude_fields=None,
for field in parameters.keys()
)

parameters = flatten(parameters.values(), types=list)
parameters.extend(pks)

n_pks = len(pks)
del pks

dbtable = '"{}"'.format(meta.db_table)

Expand All @@ -204,11 +206,37 @@ def bulk_update(objs, meta=None, update_fields=None, exclude_fields=None,
pks=', '.join(itertools.repeat('%s', n_pks)),
)

sql = 'UPDATE {dbtable} SET {values} WHERE {in_clause}'.format(
dbtable=dbtable,
values=values,
in_clause=in_clause,
)
if ordered:
columns = ', '.join('"{column}"'.format(column=field.column)
for field in parameters.keys())
parameters = list(pks) + flatten(parameters.values(), types=list)

sql = '''with cte as
(
select "{pk_column}", {columns}
from {dbtable}
where {in_clause} order by "{pk_column}" asc
)
UPDATE {dbtable}
SET {values}
from cte
where cte."{pk_column}" = {dbtable}."{pk_column}"
;'''.format(
dbtable=dbtable,
values=values,
in_clause=in_clause,
columns=columns,
pk_column=pk_field.column,
)
else:
parameters = flatten(parameters.values(), types=list)
parameters.extend(pks)
sql = 'UPDATE {dbtable} SET {values} WHERE {in_clause}'.format(
dbtable=dbtable,
values=values,
in_clause=in_clause,
)
del pks
del values

# String escaping in ANSI SQL is done by using double quotes (").
Expand Down