• Language: en
  • 1.11
  • 2.0
  • Documentation version: development

Source code for django.db.models.indexes

import hashlib

from django.utils.encoding import force_bytes

__all__ = ['Index']


[docs]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): raise ValueError('Index.fields must be a list.') if not fields: raise ValueError('At least one field is required to define an index.') self.fields = 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.""" path, args, kwargs = self.deconstruct() return self.__class__(*args, **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 = 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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