Source code for django.db.models.indexes

from django.db.backends.utils import names_digest, split_identifier
from django.db.models.query_utils import Q
from django.db.models.sql import Query

__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, opclasses=(), condition=None): if opclasses and not name: raise ValueError('An index must be named to use opclasses.') if not isinstance(condition, (type(None), Q)): raise ValueError('Index.condition must be a Q instance.') if condition and not name: raise ValueError('An index must be named to use condition.') if not isinstance(fields, (list, tuple)): raise ValueError('Index.fields must be a list or tuple.') if not isinstance(opclasses, (list, tuple)): raise ValueError('Index.opclasses must be a list or tuple.') if opclasses and len(fields) != len(opclasses): raise ValueError('Index.fields and Index.opclasses must have the same number of elements.') if not fields: raise ValueError('At least one field is required to define an index.') self.fields = list(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 self.opclasses = opclasses self.condition = condition 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_condition_sql(self, model, schema_editor): if self.condition is None: return None query = Query(model=model) query.add_q(self.condition) compiler = query.get_compiler(connection=schema_editor.connection) # Only the WhereNode is of interest for the partial index. sql, params = query.where.as_sql(compiler=compiler, connection=schema_editor.connection) # BaseDatabaseSchemaEditor does the same map on the params, but since # it's handled outside of that class, the work is done here. return sql % tuple(map(schema_editor.quote_value, params)) 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] condition = self._get_condition_sql(model, schema_editor) return schema_editor._create_index_sql( model, fields, name=self.name, using=using, db_tablespace=self.db_tablespace, col_suffixes=col_suffixes, opclasses=self.opclasses, condition=condition, ) def remove_sql(self, model, schema_editor): return schema_editor._delete_index_sql(model, 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 if self.opclasses: kwargs['opclasses'] = self.opclasses if self.condition: kwargs['condition'] = self.condition return (path, (), kwargs) def clone(self): """Create a copy of this Index.""" _, _, kwargs = self.deconstruct() return self.__class__(**kwargs) 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' % (names_digest(*hash_data, length=6), 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'%s>" % ( self.__class__.__name__, ', '.join(self.fields), '' if self.condition is None else ', condition=%s' % self.condition, ) def __eq__(self, other): return (self.__class__ == other.__class__) and (self.deconstruct() == other.deconstruct())
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