django1/django/db/models/indexes.py

114 lines
4.0 KiB
Python

from __future__ import unicode_literals
import hashlib
from django.utils.encoding import force_bytes
from django.utils.functional import cached_property
__all__ = ['Index']
# The max length of the names of the indexes (restricted to 30 due to Oracle)
MAX_NAME_LENGTH = 30
class Index(object):
suffix = 'idx'
def __init__(self, fields=[], name=None):
if not fields:
raise ValueError('At least one field is required to define an index.')
self.fields = fields
self._name = name or ''
if self._name:
errors = self.check_name()
if len(self._name) > MAX_NAME_LENGTH:
errors.append('Index names cannot be longer than %s characters.' % MAX_NAME_LENGTH)
if errors:
raise ValueError(errors)
@cached_property
def name(self):
if not self._name:
self._name = self.get_name()
self.check_name()
return self._name
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, schema_editor):
fields = [self.model._meta.get_field(field) for field in self.fields]
tablespace_sql = schema_editor._get_index_tablespace_sql(self.model, fields)
columns = [field.column for field in fields]
quote_name = schema_editor.quote_name
return schema_editor.sql_create_index % {
'table': quote_name(self.model._meta.db_table),
'name': quote_name(self.name),
'columns': ', '.join(quote_name(column) for column in columns),
'extra': tablespace_sql,
}
def remove_sql(self, schema_editor):
quote_name = schema_editor.quote_name
return schema_editor.sql_delete_index % {
'table': quote_name(self.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')
return (path, (), {'fields': self.fields})
@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 get_name(self):
"""
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 = self.model._meta.db_table
column_names = [self.model._meta.get_field(field).column for field in self.fields]
hash_data = [table_name] + column_names + [self.suffix]
index_name = '%s_%s_%s' % (
table_name[:11],
column_names[0][:7],
'%s_%s' % (self._hash_generator(*hash_data), self.suffix),
)
assert len(index_name) <= 30, (
'Index too long for multiple database support. Is self.suffix '
'longer than 3 characters?'
)
return index_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())
def __ne__(self, other):
return not (self == other)