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Code Issues 25 Releases Wiki Activity

Refs #13312 -- Simplified handling of nulls ordering on MySQL.

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MySQL & MariaDB support the standard IS NULL and IS NOT NULL so
the same workaround used for NULLS FIRST and NULLS LAST that is
used for SQLite < 3.30.0 can be used.

Thanks Simon Charette for the discussion.
This commit is contained in:
Nick Pope 2019-11-04 13:47:58 +00:00 committed by Mariusz Felisiak
parent e0e88ceaaa
commit 7286eaf681
4 changed files with 14 additions and 20 deletions
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3
django/db/backends/base/features.py
View File

@ -88,6 +88,9 @@ class BaseDatabaseFeatures:
# Does the backend order NULL values as largest or smallest?
nulls_order_largest = False
# Does the backend support NULLS FIRST and NULLS LAST in ORDER BY?
supports_order_by_nulls_modifier = True
# The database's limit on the number of query parameters.
max_query_params = None

1
django/db/backends/mysql/features.py
View File

@ -50,6 +50,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
db_functions_convert_bytes_to_str = True
# Neither MySQL nor MariaDB support partial indexes.
supports_partial_indexes = False
supports_order_by_nulls_modifier = False
@cached_property
def _mysql_storage_engine(self):

1
django/db/backends/sqlite3/features.py
View File

@ -44,3 +44,4 @@ class DatabaseFeatures(BaseDatabaseFeatures):
supports_over_clause = Database.sqlite_version_info >= (3, 25, 0)
supports_frame_range_fixed_distance = Database.sqlite_version_info >= (3, 28, 0)
supports_aggregate_filter_clause = Database.sqlite_version_info >= (3, 30, 1)
supports_order_by_nulls_modifier = Database.sqlite_version_info >= (3, 30, 0)

29
django/db/models/expressions.py
View File

@ -1128,11 +1128,17 @@ class OrderBy(BaseExpression):
return [self.expression]
def as_sql(self, compiler, connection, template=None, **extra_context):
if not template:
template = template or self.template
if connection.features.supports_order_by_nulls_modifier:
if self.nulls_last:
template = '%s NULLS LAST' % self.template
template = '%s NULLS LAST' % template
elif self.nulls_first:
template = '%s NULLS FIRST' % self.template
template = '%s NULLS FIRST' % template
else:
if self.nulls_last:
template = '%%(expression)s IS NULL, %s' % template
elif self.nulls_first:
template = '%%(expression)s IS NOT NULL, %s' % template
connection.ops.check_expression_support(self)
expression_sql, params = compiler.compile(self.expression)
placeholders = {
@ -1144,23 +1150,6 @@ class OrderBy(BaseExpression):
params *= template.count('%(expression)s')
return (template % placeholders).rstrip(), params
def as_sqlite(self, compiler, connection):
template = None
if connection.Database.sqlite_version_info < (3, 30, 0):
if self.nulls_last:
template = '%(expression)s IS NULL, %(expression)s %(ordering)s'
elif self.nulls_first:
template = '%(expression)s IS NOT NULL, %(expression)s %(ordering)s'
return self.as_sql(compiler, connection, template=template)
def as_mysql(self, compiler, connection):
template = None
if self.nulls_last:
template = 'ISNULL(%(expression)s), %(expression)s %(ordering)s '
elif self.nulls_first:
template = 'IF(ISNULL(%(expression)s),0,1), %(expression)s %(ordering)s '
return self.as_sql(compiler, connection, template=template)
def as_oracle(self, compiler, connection):
# Oracle doesn't allow ORDER BY EXISTS() unless it's wrapped in
# a CASE WHEN.