django1/django/db/backends/base/features.py

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from django.db.utils import ProgrammingError
from django.utils.functional import cached_property
class BaseDatabaseFeatures(object):
gis_enabled = False
allows_group_by_pk = False
# True if django.db.backends.utils.typecast_timestamp is used on values
# returned from dates() calls.
needs_datetime_string_cast = True
empty_fetchmany_value = []
update_can_self_select = True
# Does the backend distinguish between '' and None?
interprets_empty_strings_as_nulls = False
# Does the backend allow inserting duplicate NULL rows in a nullable
# unique field? All core backends implement this correctly, but other
# databases such as SQL Server do not.
supports_nullable_unique_constraints = True
# Does the backend allow inserting duplicate rows when a unique_together
# constraint exists and some fields are nullable but not all of them?
supports_partially_nullable_unique_constraints = True
can_use_chunked_reads = True
can_return_id_from_insert = False
has_bulk_insert = False
uses_savepoints = False
can_release_savepoints = False
can_combine_inserts_with_and_without_auto_increment_pk = False
# If True, don't use integer foreign keys referring to, e.g., positive
# integer primary keys.
related_fields_match_type = False
allow_sliced_subqueries = True
has_select_for_update = False
has_select_for_update_nowait = False
supports_select_related = True
# Does the default test database allow multiple connections?
# Usually an indication that the test database is in-memory
test_db_allows_multiple_connections = True
# Can an object be saved without an explicit primary key?
supports_unspecified_pk = False
# Can a fixture contain forward references? i.e., are
# FK constraints checked at the end of transaction, or
# at the end of each save operation?
supports_forward_references = True
# Does the backend truncate names properly when they are too long?
truncates_names = False
# Is there a REAL datatype in addition to floats/doubles?
has_real_datatype = False
supports_subqueries_in_group_by = True
supports_bitwise_or = True
# Is there a true datatype for uuid?
has_native_uuid_field = False
# Is there a true datatype for timedeltas?
has_native_duration_field = False
# Does the database driver support timedeltas as arguments?
# This is only relevant when there is a native duration field.
# Specifically, there is a bug with cx_Oracle:
# https://bitbucket.org/anthony_tuininga/cx_oracle/issue/7/
driver_supports_timedelta_args = False
# Do time/datetime fields have microsecond precision?
supports_microsecond_precision = True
# Does the __regex lookup support backreferencing and grouping?
supports_regex_backreferencing = True
# Can date/datetime lookups be performed using a string?
supports_date_lookup_using_string = True
# Can datetimes with timezones be used?
supports_timezones = True
# Does the database have a copy of the zoneinfo database?
has_zoneinfo_database = True
# When performing a GROUP BY, is an ORDER BY NULL required
# to remove any ordering?
requires_explicit_null_ordering_when_grouping = False
# Does the backend order NULL values as largest or smallest?
nulls_order_largest = False
# Is there a 1000 item limit on query parameters?
supports_1000_query_parameters = True
# Can an object have an autoincrement primary key of 0? MySQL says No.
allows_auto_pk_0 = True
# Do we need to NULL a ForeignKey out, or can the constraint check be
# deferred
can_defer_constraint_checks = False
# date_interval_sql can properly handle mixed Date/DateTime fields and timedeltas
supports_mixed_date_datetime_comparisons = True
# Does the backend support tablespaces? Default to False because it isn't
# in the SQL standard.
supports_tablespaces = False
# Does the backend reset sequences between tests?
supports_sequence_reset = True
# Can the backend determine reliably the length of a CharField?
can_introspect_max_length = True
# Can the backend determine reliably if a field is nullable?
# Note that this is separate from interprets_empty_strings_as_nulls,
# although the latter feature, when true, interferes with correct
# setting (and introspection) of CharFields' nullability.
# This is True for all core backends.
can_introspect_null = True
# Confirm support for introspected foreign keys
# Every database can do this reliably, except MySQL,
# which can't do it for MyISAM tables
can_introspect_foreign_keys = True
# Can the backend introspect an AutoField, instead of an IntegerField?
can_introspect_autofield = False
# Can the backend introspect a BigIntegerField, instead of an IntegerField?
can_introspect_big_integer_field = True
# Can the backend introspect an BinaryField, instead of an TextField?
can_introspect_binary_field = True
# Can the backend introspect an DecimalField, instead of an FloatField?
can_introspect_decimal_field = True
# Can the backend introspect an IPAddressField, instead of an CharField?
can_introspect_ip_address_field = False
# Can the backend introspect a PositiveIntegerField, instead of an IntegerField?
can_introspect_positive_integer_field = False
# Can the backend introspect a SmallIntegerField, instead of an IntegerField?
can_introspect_small_integer_field = False
# Can the backend introspect a TimeField, instead of a DateTimeField?
can_introspect_time_field = True
# Support for the DISTINCT ON clause
can_distinct_on_fields = False
# Does the backend decide to commit before SAVEPOINT statements
# when autocommit is disabled? http://bugs.python.org/issue8145#msg109965
autocommits_when_autocommit_is_off = False
# Does the backend prevent running SQL queries in broken transactions?
atomic_transactions = True
# Can we roll back DDL in a transaction?
can_rollback_ddl = False
# Can we issue more than one ALTER COLUMN clause in an ALTER TABLE?
supports_combined_alters = False
# Does it support foreign keys?
supports_foreign_keys = True
# Does it support CHECK constraints?
supports_column_check_constraints = True
# Does the backend support 'pyformat' style ("... %(name)s ...", {'name': value})
# parameter passing? Note this can be provided by the backend even if not
# supported by the Python driver
supports_paramstyle_pyformat = True
# Does the backend require literal defaults, rather than parameterized ones?
requires_literal_defaults = False
# Does the backend require a connection reset after each material schema change?
connection_persists_old_columns = False
# What kind of error does the backend throw when accessing closed cursor?
closed_cursor_error_class = ProgrammingError
# Does 'a' LIKE 'A' match?
has_case_insensitive_like = True
# Does the backend require the sqlparse library for splitting multi-line
# statements before executing them?
requires_sqlparse_for_splitting = True
# Suffix for backends that don't support "SELECT xxx;" queries.
bare_select_suffix = ''
# If NULL is implied on columns without needing to be explicitly specified
implied_column_null = False
uppercases_column_names = False
# Does the backend support "select for update" queries with limit (and offset)?
supports_select_for_update_with_limit = True
def __init__(self, connection):
self.connection = connection
@cached_property
def supports_transactions(self):
"""Confirm support for transactions."""
with self.connection.cursor() as cursor:
cursor.execute('CREATE TABLE ROLLBACK_TEST (X INT)')
self.connection.set_autocommit(False)
cursor.execute('INSERT INTO ROLLBACK_TEST (X) VALUES (8)')
self.connection.rollback()
self.connection.set_autocommit(True)
cursor.execute('SELECT COUNT(X) FROM ROLLBACK_TEST')
count, = cursor.fetchone()
cursor.execute('DROP TABLE ROLLBACK_TEST')
return count == 0
@cached_property
def supports_stddev(self):
"""Confirm support for STDDEV and related stats functions."""
class StdDevPop(object):
contains_aggregate = True
sql_function = 'STDDEV_POP'
try:
self.connection.ops.check_aggregate_support(StdDevPop())
return True
except NotImplementedError:
return False
def introspected_boolean_field_type(self, field=None, created_separately=False):
"""
What is the type returned when the backend introspects a BooleanField?
The optional arguments may be used to give further details of the field to be
introspected; in particular, they are provided by Django's test suite:
field -- the field definition
created_separately -- True if the field was added via a SchemaEditor's AddField,
False if the field was created with the model
Note that return value from this function is compared by tests against actual
introspection results; it should provide expectations, not run an introspection
itself.
"""
if self.can_introspect_null and field and field.null:
return 'NullBooleanField'
return 'BooleanField'