118 lines
4.6 KiB
Python
118 lines
4.6 KiB
Python
import hashlib
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from django.utils.encoding import force_bytes
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__all__ = ['Index']
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class Index:
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suffix = 'idx'
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# The max length of the name of the index (restricted to 30 for
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# cross-database compatibility with Oracle)
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max_name_length = 30
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def __init__(self, *, fields=[], name=None, db_tablespace=None):
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if not isinstance(fields, list):
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raise ValueError('Index.fields must be a list.')
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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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# A list of 2-tuple with the field name and ordering ('' or 'DESC').
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self.fields_orders = [
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(field_name[1:], 'DESC') if field_name.startswith('-') else (field_name, '')
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for field_name in self.fields
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]
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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) > self.max_name_length:
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errors.append('Index names cannot be longer than %s characters.' % self.max_name_length)
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if errors:
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raise ValueError(errors)
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self.db_tablespace = db_tablespace
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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, model, schema_editor, using=''):
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fields = [model._meta.get_field(field_name) for field_name, _ in self.fields_orders]
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col_suffixes = [order[1] for order in self.fields_orders]
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return schema_editor._create_index_sql(
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model, fields, name=self.name, using=using, db_tablespace=self.db_tablespace,
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col_suffixes=col_suffixes,
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)
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def remove_sql(self, model, 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(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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kwargs = {'fields': self.fields, 'name': self.name}
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if self.db_tablespace is not None:
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kwargs['db_tablespace'] = self.db_tablespace
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return (path, (), kwargs)
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def clone(self):
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"""Create a copy of this Index."""
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path, args, kwargs = self.deconstruct()
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return self.__class__(*args, **kwargs)
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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 set_name_with_model(self, model):
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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 = model._meta.db_table
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column_names = [model._meta.get_field(field_name).column for field_name, order in self.fields_orders]
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column_names_with_order = [
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(('-%s' if order else '%s') % column_name)
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for column_name, (field_name, order) in zip(column_names, self.fields_orders)
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]
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# The length of the parts of the name is based on the default max
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# length of 30 characters.
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hash_data = [table_name] + column_names_with_order + [self.suffix]
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self.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(self.name) <= self.max_name_length, (
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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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self.check_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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