290 lines
10 KiB
Python
290 lines
10 KiB
Python
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from django.db.models.aggregates import StdDev
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from django.db.utils import NotSupportedError, ProgrammingError
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from django.utils.functional import cached_property
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class BaseDatabaseFeatures:
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gis_enabled = False
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allows_group_by_pk = False
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allows_group_by_selected_pks = False
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empty_fetchmany_value = []
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update_can_self_select = True
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# Does the backend distinguish between '' and None?
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interprets_empty_strings_as_nulls = False
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# Does the backend allow inserting duplicate NULL rows in a nullable
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# unique field? All core backends implement this correctly, but other
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# databases such as SQL Server do not.
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supports_nullable_unique_constraints = True
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# Does the backend allow inserting duplicate rows when a unique_together
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# constraint exists and some fields are nullable but not all of them?
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supports_partially_nullable_unique_constraints = True
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can_use_chunked_reads = True
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can_return_id_from_insert = False
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can_return_ids_from_bulk_insert = False
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has_bulk_insert = True
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uses_savepoints = False
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can_release_savepoints = False
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# If True, don't use integer foreign keys referring to, e.g., positive
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# integer primary keys.
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related_fields_match_type = False
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allow_sliced_subqueries_with_in = True
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has_select_for_update = False
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has_select_for_update_nowait = False
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has_select_for_update_skip_locked = False
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has_select_for_update_of = False
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# Does the database's SELECT FOR UPDATE OF syntax require a column rather
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# than a table?
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select_for_update_of_column = False
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# Does the default test database allow multiple connections?
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# Usually an indication that the test database is in-memory
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test_db_allows_multiple_connections = True
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# Can an object be saved without an explicit primary key?
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supports_unspecified_pk = False
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# Can a fixture contain forward references? i.e., are
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# FK constraints checked at the end of transaction, or
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# at the end of each save operation?
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supports_forward_references = True
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# Does the backend truncate names properly when they are too long?
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truncates_names = False
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# Is there a REAL datatype in addition to floats/doubles?
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has_real_datatype = False
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supports_subqueries_in_group_by = True
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# Is there a true datatype for uuid?
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has_native_uuid_field = False
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# Is there a true datatype for timedeltas?
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has_native_duration_field = False
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# Does the database driver supports same type temporal data subtraction
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# by returning the type used to store duration field?
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supports_temporal_subtraction = False
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# Does the __regex lookup support backreferencing and grouping?
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supports_regex_backreferencing = True
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# Can date/datetime lookups be performed using a string?
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supports_date_lookup_using_string = True
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# Can datetimes with timezones be used?
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supports_timezones = True
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# Does the database have a copy of the zoneinfo database?
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has_zoneinfo_database = True
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# When performing a GROUP BY, is an ORDER BY NULL required
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# to remove any ordering?
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requires_explicit_null_ordering_when_grouping = False
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# Does the backend order NULL values as largest or smallest?
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nulls_order_largest = False
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# The database's limit on the number of query parameters.
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max_query_params = None
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# Can an object have an autoincrement primary key of 0? MySQL says No.
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allows_auto_pk_0 = True
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# Do we need to NULL a ForeignKey out, or can the constraint check be
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# deferred
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can_defer_constraint_checks = False
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# date_interval_sql can properly handle mixed Date/DateTime fields and timedeltas
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supports_mixed_date_datetime_comparisons = True
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# Does the backend support tablespaces? Default to False because it isn't
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# in the SQL standard.
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supports_tablespaces = False
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# Does the backend reset sequences between tests?
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supports_sequence_reset = True
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# Can the backend introspect the default value of a column?
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can_introspect_default = True
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# Confirm support for introspected foreign keys
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# Every database can do this reliably, except MySQL,
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# which can't do it for MyISAM tables
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can_introspect_foreign_keys = True
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# Can the backend introspect an AutoField, instead of an IntegerField?
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can_introspect_autofield = False
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# Can the backend introspect a BigIntegerField, instead of an IntegerField?
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can_introspect_big_integer_field = True
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# Can the backend introspect an BinaryField, instead of an TextField?
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can_introspect_binary_field = True
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# Can the backend introspect an DecimalField, instead of an FloatField?
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can_introspect_decimal_field = True
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# Can the backend introspect an IPAddressField, instead of an CharField?
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can_introspect_ip_address_field = False
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# Can the backend introspect a PositiveIntegerField, instead of an IntegerField?
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can_introspect_positive_integer_field = False
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# Can the backend introspect a SmallIntegerField, instead of an IntegerField?
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can_introspect_small_integer_field = False
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# Can the backend introspect a TimeField, instead of a DateTimeField?
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can_introspect_time_field = True
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# Some backends may not be able to differentiate BooleanField from other
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# fields such as IntegerField.
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introspected_boolean_field_type = 'BooleanField'
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# Can the backend introspect the column order (ASC/DESC) for indexes?
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supports_index_column_ordering = True
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# Support for the DISTINCT ON clause
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can_distinct_on_fields = False
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# Does the backend decide to commit before SAVEPOINT statements
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# when autocommit is disabled? https://bugs.python.org/issue8145#msg109965
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autocommits_when_autocommit_is_off = False
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# Does the backend prevent running SQL queries in broken transactions?
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atomic_transactions = True
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# Can we roll back DDL in a transaction?
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can_rollback_ddl = False
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# Does it support operations requiring references rename in a transaction?
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supports_atomic_references_rename = True
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# Can we issue more than one ALTER COLUMN clause in an ALTER TABLE?
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supports_combined_alters = False
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# Does it support foreign keys?
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supports_foreign_keys = True
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# Does it support CHECK constraints?
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supports_column_check_constraints = True
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# Does the backend support 'pyformat' style ("... %(name)s ...", {'name': value})
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# parameter passing? Note this can be provided by the backend even if not
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# supported by the Python driver
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supports_paramstyle_pyformat = True
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# Does the backend require literal defaults, rather than parameterized ones?
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requires_literal_defaults = False
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# Does the backend require a connection reset after each material schema change?
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connection_persists_old_columns = False
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# What kind of error does the backend throw when accessing closed cursor?
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closed_cursor_error_class = ProgrammingError
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# Does 'a' LIKE 'A' match?
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has_case_insensitive_like = True
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# Does the backend require the sqlparse library for splitting multi-line
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# statements before executing them?
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requires_sqlparse_for_splitting = True
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# Suffix for backends that don't support "SELECT xxx;" queries.
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bare_select_suffix = ''
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# If NULL is implied on columns without needing to be explicitly specified
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implied_column_null = False
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uppercases_column_names = False
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# Does the backend support "select for update" queries with limit (and offset)?
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supports_select_for_update_with_limit = True
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# Does the backend ignore null expressions in GREATEST and LEAST queries unless
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# every expression is null?
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greatest_least_ignores_nulls = False
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# Can the backend clone databases for parallel test execution?
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# Defaults to False to allow third-party backends to opt-in.
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can_clone_databases = False
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# Does the backend consider table names with different casing to
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# be equal?
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ignores_table_name_case = False
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# Place FOR UPDATE right after FROM clause. Used on MSSQL.
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for_update_after_from = False
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# Combinatorial flags
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supports_select_union = True
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supports_select_intersection = True
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supports_select_difference = True
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supports_slicing_ordering_in_compound = False
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# Does the database support SQL 2003 FILTER (WHERE ...) in aggregate
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# expressions?
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supports_aggregate_filter_clause = False
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# Does the backend support indexing a TextField?
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supports_index_on_text_field = True
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# Does the backed support window expressions (expression OVER (...))?
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supports_over_clause = False
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# Does the backend support CAST with precision?
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supports_cast_with_precision = True
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# SQL to create a procedure for use by the Django test suite. The
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# functionality of the procedure isn't important.
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create_test_procedure_without_params_sql = None
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create_test_procedure_with_int_param_sql = None
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# Does the backend support keyword parameters for cursor.callproc()?
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supports_callproc_kwargs = False
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# Convert CharField results from bytes to str in database functions.
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db_functions_convert_bytes_to_str = False
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# What formats does the backend EXPLAIN syntax support?
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supported_explain_formats = set()
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# Does DatabaseOperations.explain_query_prefix() raise ValueError if
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# unknown kwargs are passed to QuerySet.explain()?
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validates_explain_options = True
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def __init__(self, connection):
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self.connection = connection
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@cached_property
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def supports_explaining_query_execution(self):
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"""Does this backend support explaining query execution?"""
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return self.connection.ops.explain_prefix is not None
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@cached_property
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def supports_transactions(self):
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"""Confirm support for transactions."""
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with self.connection.cursor() as cursor:
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cursor.execute('CREATE TABLE ROLLBACK_TEST (X INT)')
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self.connection.set_autocommit(False)
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cursor.execute('INSERT INTO ROLLBACK_TEST (X) VALUES (8)')
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self.connection.rollback()
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self.connection.set_autocommit(True)
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cursor.execute('SELECT COUNT(X) FROM ROLLBACK_TEST')
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count, = cursor.fetchone()
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cursor.execute('DROP TABLE ROLLBACK_TEST')
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return count == 0
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@cached_property
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def supports_stddev(self):
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"""Confirm support for STDDEV and related stats functions."""
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try:
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self.connection.ops.check_expression_support(StdDev(1))
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except NotSupportedError:
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return False
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return True
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