from django.db.backends.utils import names_digest, split_identifier
from django.db.models.query_utils import Q
from django.db.models.sql import Query
__all__ = ['Index']
[文档]class Index:
suffix = 'idx'
# The max length of the name of the index (restricted to 30 for
# cross-database compatibility with Oracle)
max_name_length = 30
def __init__(self, *, fields=(), name=None, db_tablespace=None, opclasses=(), condition=None):
if opclasses and not name:
raise ValueError('An index must be named to use opclasses.')
if not isinstance(condition, (type(None), Q)):
raise ValueError('Index.condition must be a Q instance.')
if condition and not name:
raise ValueError('An index must be named to use condition.')
if not isinstance(fields, (list, tuple)):
raise ValueError('Index.fields must be a list or tuple.')
if not isinstance(opclasses, (list, tuple)):
raise ValueError('Index.opclasses must be a list or tuple.')
if opclasses and len(fields) != len(opclasses):
raise ValueError('Index.fields and Index.opclasses must have the same number of elements.')
if not fields:
raise ValueError('At least one field is required to define an index.')
self.fields = list(fields)
# A list of 2-tuple with the field name and ordering ('' or 'DESC').
self.fields_orders = [
(field_name[1:], 'DESC') if field_name.startswith('-') else (field_name, '')
for field_name in self.fields
]
self.name = name or ''
if self.name:
errors = self.check_name()
if len(self.name) > self.max_name_length:
errors.append('Index names cannot be longer than %s characters.' % self.max_name_length)
if errors:
raise ValueError(errors)
self.db_tablespace = db_tablespace
self.opclasses = opclasses
self.condition = condition
def check_name(self):
errors = []
# Name can't start with an underscore on Oracle; prepend D if needed.
if self.name[0] == '_':
errors.append('Index names cannot start with an underscore (_).')
self.name = 'D%s' % self.name[1:]
# Name can't start with a number on Oracle; prepend D if needed.
elif self.name[0].isdigit():
errors.append('Index names cannot start with a number (0-9).')
self.name = 'D%s' % self.name[1:]
return errors
def _get_condition_sql(self, model, schema_editor):
if self.condition is None:
return None
query = Query(model=model)
where = query.build_where(self.condition)
compiler = query.get_compiler(connection=schema_editor.connection)
sql, params = where.as_sql(compiler, schema_editor.connection)
return sql % tuple(schema_editor.quote_value(p) for p in params)
def create_sql(self, model, schema_editor, using=''):
fields = [model._meta.get_field(field_name) for field_name, _ in self.fields_orders]
col_suffixes = [order[1] for order in self.fields_orders]
condition = self._get_condition_sql(model, schema_editor)
return schema_editor._create_index_sql(
model, fields, name=self.name, using=using, db_tablespace=self.db_tablespace,
col_suffixes=col_suffixes, opclasses=self.opclasses, condition=condition,
)
def remove_sql(self, model, schema_editor):
return schema_editor._delete_index_sql(model, self.name)
def deconstruct(self):
path = '%s.%s' % (self.__class__.__module__, self.__class__.__name__)
path = path.replace('django.db.models.indexes', 'django.db.models')
kwargs = {'fields': self.fields, 'name': self.name}
if self.db_tablespace is not None:
kwargs['db_tablespace'] = self.db_tablespace
if self.opclasses:
kwargs['opclasses'] = self.opclasses
if self.condition:
kwargs['condition'] = self.condition
return (path, (), kwargs)
def clone(self):
"""Create a copy of this Index."""
_, _, kwargs = self.deconstruct()
return self.__class__(**kwargs)
def set_name_with_model(self, model):
"""
Generate a unique name for the index.
The name is divided into 3 parts - table name (12 chars), field name
(8 chars) and unique hash + suffix (10 chars). Each part is made to
fit its size by truncating the excess length.
"""
_, table_name = split_identifier(model._meta.db_table)
column_names = [model._meta.get_field(field_name).column for field_name, order in self.fields_orders]
column_names_with_order = [
(('-%s' if order else '%s') % column_name)
for column_name, (field_name, order) in zip(column_names, self.fields_orders)
]
# The length of the parts of the name is based on the default max
# length of 30 characters.
hash_data = [table_name] + column_names_with_order + [self.suffix]
self.name = '%s_%s_%s' % (
table_name[:11],
column_names[0][:7],
'%s_%s' % (names_digest(*hash_data, length=6), self.suffix),
)
assert len(self.name) <= self.max_name_length, (
'Index too long for multiple database support. Is self.suffix '
'longer than 3 characters?'
)
self.check_name()
def __repr__(self):
return "<%s: fields='%s'%s>" % (
self.__class__.__name__, ', '.join(self.fields),
'' if self.condition is None else ', condition=%s' % self.condition,
)
def __eq__(self, other):
return (self.__class__ == other.__class__) and (self.deconstruct() == other.deconstruct())
