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from __future__ import unicode_literals
import hashlib
from django.db.backends.utils import split_identifier
from django.utils.encoding import force_bytes
__all__ = [str('Index')]
class Index(object):
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):
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)
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_sql_create_template_values(self, model, schema_editor, using):
fields = [model._meta.get_field(field_name) for field_name, order in self.fields_orders]
tablespace_sql = schema_editor._get_index_tablespace_sql(model, fields)
quote_name = schema_editor.quote_name
columns = [
('%s %s' % (quote_name(field.column), order)).strip()
for field, (field_name, order) in zip(fields, self.fields_orders)
]
return {
'table': quote_name(model._meta.db_table),
'name': quote_name(self.name),
'columns': ', '.join(columns),
'using': using,
'extra': tablespace_sql,
}
def create_sql(self, model, schema_editor, using=''):
sql_create_index = schema_editor.sql_create_index
sql_parameters = self.get_sql_create_template_values(model, schema_editor, using)
return sql_create_index % sql_parameters
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')
return (path, (), {'fields': self.fields, 'name': self.name})
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 = 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())
def __ne__(self, other):
return not (self == other)
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