114 lines
4.0 KiB
Python
114 lines
4.0 KiB
Python
from __future__ import unicode_literals
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import hashlib
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from django.utils.encoding import force_bytes
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from django.utils.functional import cached_property
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__all__ = ['Index']
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# The max length of the names of the indexes (restricted to 30 due to Oracle)
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MAX_NAME_LENGTH = 30
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class Index(object):
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suffix = 'idx'
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def __init__(self, fields=[], name=None):
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if not fields:
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raise ValueError('At least one field is required to define an index.')
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self.fields = fields
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self._name = name or ''
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if self._name:
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errors = self.check_name()
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if len(self._name) > MAX_NAME_LENGTH:
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errors.append('Index names cannot be longer than %s characters.' % MAX_NAME_LENGTH)
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if errors:
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raise ValueError(errors)
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@cached_property
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def name(self):
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if not self._name:
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self._name = self.get_name()
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self.check_name()
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return self._name
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def check_name(self):
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errors = []
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# Name can't start with an underscore on Oracle; prepend D if needed.
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if self._name[0] == '_':
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errors.append('Index names cannot start with an underscore (_).')
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self._name = 'D%s' % self._name[1:]
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# Name can't start with a number on Oracle; prepend D if needed.
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elif self._name[0].isdigit():
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errors.append('Index names cannot start with a number (0-9).')
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self._name = 'D%s' % self._name[1:]
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return errors
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def create_sql(self, schema_editor):
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fields = [self.model._meta.get_field(field) for field in self.fields]
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tablespace_sql = schema_editor._get_index_tablespace_sql(self.model, fields)
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columns = [field.column for field in fields]
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quote_name = schema_editor.quote_name
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return schema_editor.sql_create_index % {
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'table': quote_name(self.model._meta.db_table),
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'name': quote_name(self.name),
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'columns': ', '.join(quote_name(column) for column in columns),
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'extra': tablespace_sql,
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}
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def remove_sql(self, schema_editor):
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quote_name = schema_editor.quote_name
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return schema_editor.sql_delete_index % {
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'table': quote_name(self.model._meta.db_table),
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'name': quote_name(self.name),
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}
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def deconstruct(self):
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path = '%s.%s' % (self.__class__.__module__, self.__class__.__name__)
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path = path.replace('django.db.models.indexes', 'django.db.models')
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return (path, (), {'fields': self.fields})
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@staticmethod
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def _hash_generator(*args):
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"""
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Generate a 32-bit digest of a set of arguments that can be used to
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shorten identifying names.
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"""
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h = hashlib.md5()
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for arg in args:
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h.update(force_bytes(arg))
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return h.hexdigest()[:6]
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def get_name(self):
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"""
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Generate a unique name for the index.
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The name is divided into 3 parts - table name (12 chars), field name
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(8 chars) and unique hash + suffix (10 chars). Each part is made to
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fit its size by truncating the excess length.
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"""
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table_name = self.model._meta.db_table
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column_names = [self.model._meta.get_field(field).column for field in self.fields]
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hash_data = [table_name] + column_names + [self.suffix]
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index_name = '%s_%s_%s' % (
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table_name[:11],
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column_names[0][:7],
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'%s_%s' % (self._hash_generator(*hash_data), self.suffix),
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)
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assert len(index_name) <= 30, (
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'Index too long for multiple database support. Is self.suffix '
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'longer than 3 characters?'
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)
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return index_name
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def __repr__(self):
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return "<%s: fields='%s'>" % (self.__class__.__name__, ', '.join(self.fields))
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def __eq__(self, other):
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return (self.__class__ == other.__class__) and (self.deconstruct() == other.deconstruct())
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def __ne__(self, other):
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return not (self == other)
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