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- import hashlib
-
- from django.db.backends.utils import split_identifier
- from django.utils.encoding import force_bytes
-
- __all__ = ['Index']
-
-
- 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):
- if not isinstance(fields, (list, tuple)):
- raise ValueError('Index.fields must be a list or tuple.')
- 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
-
- 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 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]
- return schema_editor._create_index_sql(
- model, fields, name=self.name, using=using, db_tablespace=self.db_tablespace,
- col_suffixes=col_suffixes,
- )
-
- def remove_sql(self, model, schema_editor):
- quote_name = schema_editor.quote_name
- return schema_editor.sql_delete_index % {
- 'table': quote_name(model._meta.db_table),
- 'name': quote_name(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
- return (path, (), kwargs)
-
- def clone(self):
- """Create a copy of this Index."""
- _, _, kwargs = self.deconstruct()
- return self.__class__(**kwargs)
-
- @staticmethod
- def _hash_generator(*args):
- """
- Generate a 32-bit digest of a set of arguments that can be used to
- shorten identifying names.
- """
- h = hashlib.md5()
- for arg in args:
- h.update(force_bytes(arg))
- return h.hexdigest()[:6]
-
- 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' % (self._hash_generator(*hash_data), 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'>" % (self.__class__.__name__, ', '.join(self.fields))
-
- def __eq__(self, other):
- return (self.__class__ == other.__class__) and (self.deconstruct() == other.deconstruct())
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