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Diffstat (limited to 'webapp/django/db/models/sql/query.py')
| -rw-r--r-- | webapp/django/db/models/sql/query.py | 1705 |
1 files changed, 1705 insertions, 0 deletions
diff --git a/webapp/django/db/models/sql/query.py b/webapp/django/db/models/sql/query.py new file mode 100644 index 0000000000..287890a63e --- /dev/null +++ b/webapp/django/db/models/sql/query.py @@ -0,0 +1,1705 @@ +""" +Create SQL statements for QuerySets. + +The code in here encapsulates all of the SQL construction so that QuerySets +themselves do not have to (and could be backed by things other than SQL +databases). The abstraction barrier only works one way: this module has to know +all about the internals of models in order to get the information it needs. +""" + +from copy import deepcopy + +from django.utils.tree import Node +from django.utils.datastructures import SortedDict +from django.utils.encoding import force_unicode +from django.db import connection +from django.db.models import signals +from django.db.models.fields import FieldDoesNotExist +from django.db.models.query_utils import select_related_descend +from django.db.models.sql.where import WhereNode, EverythingNode, AND, OR +from django.db.models.sql.datastructures import Count +from django.core.exceptions import FieldError +from datastructures import EmptyResultSet, Empty, MultiJoin +from constants import * + +try: + set +except NameError: + from sets import Set as set # Python 2.3 fallback + +__all__ = ['Query'] + +class Query(object): + """ + A single SQL query. + """ + # SQL join types. These are part of the class because their string forms + # vary from database to database and can be customised by a subclass. + INNER = 'INNER JOIN' + LOUTER = 'LEFT OUTER JOIN' + + alias_prefix = 'T' + query_terms = QUERY_TERMS + + def __init__(self, model, connection, where=WhereNode): + self.model = model + self.connection = connection + self.alias_refcount = {} + self.alias_map = {} # Maps alias to join information + self.table_map = {} # Maps table names to list of aliases. + self.join_map = {} + self.rev_join_map = {} # Reverse of join_map. + self.quote_cache = {} + self.default_cols = True + self.default_ordering = True + self.standard_ordering = True + self.ordering_aliases = [] + self.start_meta = None + self.select_fields = [] + self.related_select_fields = [] + self.dupe_avoidance = {} + self.used_aliases = set() + self.filter_is_sticky = False + + # SQL-related attributes + self.select = [] + self.tables = [] # Aliases in the order they are created. + self.where = where() + self.where_class = where + self.group_by = [] + self.having = [] + self.order_by = [] + self.low_mark, self.high_mark = 0, None # Used for offset/limit + self.distinct = False + self.select_related = False + self.related_select_cols = [] + + # Arbitrary maximum limit for select_related. Prevents infinite + # recursion. Can be changed by the depth parameter to select_related(). + self.max_depth = 5 + + # These are for extensions. The contents are more or less appended + # verbatim to the appropriate clause. + self.extra_select = SortedDict() # Maps col_alias -> (col_sql, params). + self.extra_tables = () + self.extra_where = () + self.extra_params = () + self.extra_order_by = () + + def __str__(self): + """ + Returns the query as a string of SQL with the parameter values + substituted in. + + Parameter values won't necessarily be quoted correctly, since that is + done by the database interface at execution time. + """ + sql, params = self.as_sql() + return sql % params + + def __deepcopy__(self, memo): + result= self.clone() + memo[id(self)] = result + return result + + def __getstate__(self): + """ + Pickling support. + """ + obj_dict = self.__dict__.copy() + obj_dict['related_select_fields'] = [] + obj_dict['related_select_cols'] = [] + del obj_dict['connection'] + return obj_dict + + def __setstate__(self, obj_dict): + """ + Unpickling support. + """ + self.__dict__.update(obj_dict) + # XXX: Need a better solution for this when multi-db stuff is + # supported. It's the only class-reference to the module-level + # connection variable. + self.connection = connection + + def get_meta(self): + """ + Returns the Options instance (the model._meta) from which to start + processing. Normally, this is self.model._meta, but it can change. + """ + if self.start_meta: + return self.start_meta + return self.model._meta + + def quote_name_unless_alias(self, name): + """ + A wrapper around connection.ops.quote_name that doesn't quote aliases + for table names. This avoids problems with some SQL dialects that treat + quoted strings specially (e.g. PostgreSQL). + """ + if name in self.quote_cache: + return self.quote_cache[name] + if ((name in self.alias_map and name not in self.table_map) or + name in self.extra_select): + self.quote_cache[name] = name + return name + r = self.connection.ops.quote_name(name) + self.quote_cache[name] = r + return r + + def clone(self, klass=None, **kwargs): + """ + Creates a copy of the current instance. The 'kwargs' parameter can be + used by clients to update attributes after copying has taken place. + """ + obj = Empty() + obj.__class__ = klass or self.__class__ + obj.model = self.model + obj.connection = self.connection + obj.alias_refcount = self.alias_refcount.copy() + obj.alias_map = self.alias_map.copy() + obj.table_map = self.table_map.copy() + obj.join_map = self.join_map.copy() + obj.rev_join_map = self.rev_join_map.copy() + obj.quote_cache = {} + obj.default_cols = self.default_cols + obj.default_ordering = self.default_ordering + obj.standard_ordering = self.standard_ordering + obj.ordering_aliases = [] + obj.start_meta = self.start_meta + obj.select_fields = self.select_fields[:] + obj.related_select_fields = self.related_select_fields[:] + obj.dupe_avoidance = self.dupe_avoidance.copy() + obj.select = self.select[:] + obj.tables = self.tables[:] + obj.where = deepcopy(self.where) + obj.where_class = self.where_class + obj.group_by = self.group_by[:] + obj.having = self.having[:] + obj.order_by = self.order_by[:] + obj.low_mark, obj.high_mark = self.low_mark, self.high_mark + obj.distinct = self.distinct + obj.select_related = self.select_related + obj.related_select_cols = [] + obj.max_depth = self.max_depth + obj.extra_select = self.extra_select.copy() + obj.extra_tables = self.extra_tables + obj.extra_where = self.extra_where + obj.extra_params = self.extra_params + obj.extra_order_by = self.extra_order_by + if self.filter_is_sticky and self.used_aliases: + obj.used_aliases = self.used_aliases.copy() + else: + obj.used_aliases = set() + obj.filter_is_sticky = False + obj.__dict__.update(kwargs) + if hasattr(obj, '_setup_query'): + obj._setup_query() + return obj + + def results_iter(self): + """ + Returns an iterator over the results from executing this query. + """ + resolve_columns = hasattr(self, 'resolve_columns') + fields = None + for rows in self.execute_sql(MULTI): + for row in rows: + if resolve_columns: + if fields is None: + # We only set this up here because + # related_select_fields isn't populated until + # execute_sql() has been called. + if self.select_fields: + fields = self.select_fields + self.related_select_fields + else: + fields = self.model._meta.fields + row = self.resolve_columns(row, fields) + yield row + + def get_count(self): + """ + Performs a COUNT() query using the current filter constraints. + """ + from subqueries import CountQuery + obj = self.clone() + obj.clear_ordering(True) + obj.clear_limits() + obj.select_related = False + obj.related_select_cols = [] + obj.related_select_fields = [] + if len(obj.select) > 1: + obj = self.clone(CountQuery, _query=obj, where=self.where_class(), + distinct=False) + obj.select = [] + obj.extra_select = SortedDict() + obj.add_count_column() + data = obj.execute_sql(SINGLE) + if not data: + return 0 + number = data[0] + + # Apply offset and limit constraints manually, since using LIMIT/OFFSET + # in SQL (in variants that provide them) doesn't change the COUNT + # output. + number = max(0, number - self.low_mark) + if self.high_mark: + number = min(number, self.high_mark - self.low_mark) + + return number + + def as_sql(self, with_limits=True, with_col_aliases=False): + """ + Creates the SQL for this query. Returns the SQL string and list of + parameters. + + If 'with_limits' is False, any limit/offset information is not included + in the query. + """ + self.pre_sql_setup() + out_cols = self.get_columns(with_col_aliases) + ordering = self.get_ordering() + + # This must come after 'select' and 'ordering' -- see docstring of + # get_from_clause() for details. + from_, f_params = self.get_from_clause() + + where, w_params = self.where.as_sql(qn=self.quote_name_unless_alias) + params = [] + for val in self.extra_select.itervalues(): + params.extend(val[1]) + + result = ['SELECT'] + if self.distinct: + result.append('DISTINCT') + result.append(', '.join(out_cols + self.ordering_aliases)) + + result.append('FROM') + result.extend(from_) + params.extend(f_params) + + if where: + result.append('WHERE %s' % where) + params.extend(w_params) + if self.extra_where: + if not where: + result.append('WHERE') + else: + result.append('AND') + result.append(' AND '.join(self.extra_where)) + + if self.group_by: + grouping = self.get_grouping() + result.append('GROUP BY %s' % ', '.join(grouping)) + + if ordering: + result.append('ORDER BY %s' % ', '.join(ordering)) + + if with_limits: + if self.high_mark is not None: + result.append('LIMIT %d' % (self.high_mark - self.low_mark)) + if self.low_mark: + if self.high_mark is None: + val = self.connection.ops.no_limit_value() + if val: + result.append('LIMIT %d' % val) + result.append('OFFSET %d' % self.low_mark) + + params.extend(self.extra_params) + return ' '.join(result), tuple(params) + + def combine(self, rhs, connector): + """ + Merge the 'rhs' query into the current one (with any 'rhs' effects + being applied *after* (that is, "to the right of") anything in the + current query. 'rhs' is not modified during a call to this function. + + The 'connector' parameter describes how to connect filters from the + 'rhs' query. + """ + assert self.model == rhs.model, \ + "Cannot combine queries on two different base models." + assert self.can_filter(), \ + "Cannot combine queries once a slice has been taken." + assert self.distinct == rhs.distinct, \ + "Cannot combine a unique query with a non-unique query." + + # Work out how to relabel the rhs aliases, if necessary. + change_map = {} + used = set() + conjunction = (connector == AND) + first = True + for alias in rhs.tables: + if not rhs.alias_refcount[alias]: + # An unused alias. + continue + promote = (rhs.alias_map[alias][JOIN_TYPE] == self.LOUTER) + new_alias = self.join(rhs.rev_join_map[alias], + (conjunction and not first), used, promote, not conjunction) + used.add(new_alias) + change_map[alias] = new_alias + first = False + + # So that we don't exclude valid results in an "or" query combination, + # the first join that is exclusive to the lhs (self) must be converted + # to an outer join. + if not conjunction: + for alias in self.tables[1:]: + if self.alias_refcount[alias] == 1: + self.promote_alias(alias, True) + break + + # Now relabel a copy of the rhs where-clause and add it to the current + # one. + if rhs.where: + w = deepcopy(rhs.where) + w.relabel_aliases(change_map) + if not self.where: + # Since 'self' matches everything, add an explicit "include + # everything" where-constraint so that connections between the + # where clauses won't exclude valid results. + self.where.add(EverythingNode(), AND) + elif self.where: + # rhs has an empty where clause. + w = self.where_class() + w.add(EverythingNode(), AND) + else: + w = self.where_class() + self.where.add(w, connector) + + # Selection columns and extra extensions are those provided by 'rhs'. + self.select = [] + for col in rhs.select: + if isinstance(col, (list, tuple)): + self.select.append((change_map.get(col[0], col[0]), col[1])) + else: + item = deepcopy(col) + item.relabel_aliases(change_map) + self.select.append(item) + self.select_fields = rhs.select_fields[:] + + if connector == OR: + # It would be nice to be able to handle this, but the queries don't + # really make sense (or return consistent value sets). Not worth + # the extra complexity when you can write a real query instead. + if self.extra_select and rhs.extra_select: + raise ValueError("When merging querysets using 'or', you " + "cannot have extra(select=...) on both sides.") + if self.extra_where and rhs.extra_where: + raise ValueError("When merging querysets using 'or', you " + "cannot have extra(where=...) on both sides.") + self.extra_select.update(rhs.extra_select) + self.extra_tables += rhs.extra_tables + self.extra_where += rhs.extra_where + self.extra_params += rhs.extra_params + + # Ordering uses the 'rhs' ordering, unless it has none, in which case + # the current ordering is used. + self.order_by = rhs.order_by and rhs.order_by[:] or self.order_by + self.extra_order_by = rhs.extra_order_by or self.extra_order_by + + def pre_sql_setup(self): + """ + Does any necessary class setup immediately prior to producing SQL. This + is for things that can't necessarily be done in __init__ because we + might not have all the pieces in place at that time. + """ + if not self.tables: + self.join((None, self.model._meta.db_table, None, None)) + if self.select_related and not self.related_select_cols: + self.fill_related_selections() + + def get_columns(self, with_aliases=False): + """ + Return the list of columns to use in the select statement. If no + columns have been specified, returns all columns relating to fields in + the model. + + If 'with_aliases' is true, any column names that are duplicated + (without the table names) are given unique aliases. This is needed in + some cases to avoid ambiguitity with nested queries. + """ + qn = self.quote_name_unless_alias + qn2 = self.connection.ops.quote_name + result = ['(%s) AS %s' % (col[0], qn2(alias)) for alias, col in self.extra_select.iteritems()] + aliases = set(self.extra_select.keys()) + if with_aliases: + col_aliases = aliases.copy() + else: + col_aliases = set() + if self.select: + for col in self.select: + if isinstance(col, (list, tuple)): + r = '%s.%s' % (qn(col[0]), qn(col[1])) + if with_aliases and col[1] in col_aliases: + c_alias = 'Col%d' % len(col_aliases) + result.append('%s AS %s' % (r, c_alias)) + aliases.add(c_alias) + col_aliases.add(c_alias) + else: + result.append(r) + aliases.add(r) + col_aliases.add(col[1]) + else: + result.append(col.as_sql(quote_func=qn)) + if hasattr(col, 'alias'): + aliases.add(col.alias) + col_aliases.add(col.alias) + elif self.default_cols: + cols, new_aliases = self.get_default_columns(with_aliases, + col_aliases) + result.extend(cols) + aliases.update(new_aliases) + for table, col in self.related_select_cols: + r = '%s.%s' % (qn(table), qn(col)) + if with_aliases and col in col_aliases: + c_alias = 'Col%d' % len(col_aliases) + result.append('%s AS %s' % (r, c_alias)) + aliases.add(c_alias) + col_aliases.add(c_alias) + else: + result.append(r) + aliases.add(r) + col_aliases.add(col) + + self._select_aliases = aliases + return result + + def get_default_columns(self, with_aliases=False, col_aliases=None, + start_alias=None, opts=None, as_pairs=False): + """ + Computes the default columns for selecting every field in the base + model. + + Returns a list of strings, quoted appropriately for use in SQL + directly, as well as a set of aliases used in the select statement (if + 'as_pairs' is True, returns a list of (alias, col_name) pairs instead + of strings as the first component and None as the second component). + """ + result = [] + if opts is None: + opts = self.model._meta + if start_alias: + table_alias = start_alias + else: + table_alias = self.tables[0] + root_pk = opts.pk.column + seen = {None: table_alias} + qn = self.quote_name_unless_alias + qn2 = self.connection.ops.quote_name + aliases = set() + for field, model in opts.get_fields_with_model(): + try: + alias = seen[model] + except KeyError: + alias = self.join((table_alias, model._meta.db_table, + root_pk, model._meta.pk.column)) + seen[model] = alias + if as_pairs: + result.append((alias, field.column)) + continue + if with_aliases and field.column in col_aliases: + c_alias = 'Col%d' % len(col_aliases) + result.append('%s.%s AS %s' % (qn(alias), + qn2(field.column), c_alias)) + col_aliases.add(c_alias) + aliases.add(c_alias) + else: + r = '%s.%s' % (qn(alias), qn2(field.column)) + result.append(r) + aliases.add(r) + if with_aliases: + col_aliases.add(field.column) + if as_pairs: + return result, None + return result, aliases + + def get_from_clause(self): + """ + Returns a list of strings that are joined together to go after the + "FROM" part of the query, as well as a list any extra parameters that + need to be included. Sub-classes, can override this to create a + from-clause via a "select", for example (e.g. CountQuery). + + This should only be called after any SQL construction methods that + might change the tables we need. This means the select columns and + ordering must be done first. + """ + result = [] + qn = self.quote_name_unless_alias + qn2 = self.connection.ops.quote_name + first = True + for alias in self.tables: + if not self.alias_refcount[alias]: + continue + try: + name, alias, join_type, lhs, lhs_col, col, nullable = self.alias_map[alias] + except KeyError: + # Extra tables can end up in self.tables, but not in the + # alias_map if they aren't in a join. That's OK. We skip them. + continue + alias_str = (alias != name and ' %s' % alias or '') + if join_type and not first: + result.append('%s %s%s ON (%s.%s = %s.%s)' + % (join_type, qn(name), alias_str, qn(lhs), + qn2(lhs_col), qn(alias), qn2(col))) + else: + connector = not first and ', ' or '' + result.append('%s%s%s' % (connector, qn(name), alias_str)) + first = False + for t in self.extra_tables: + alias, unused = self.table_alias(t) + # Only add the alias if it's not already present (the table_alias() + # calls increments the refcount, so an alias refcount of one means + # this is the only reference. + if alias not in self.alias_map or self.alias_refcount[alias] == 1: + connector = not first and ', ' or '' + result.append('%s%s' % (connector, qn(alias))) + first = False + return result, [] + + def get_grouping(self): + """ + Returns a tuple representing the SQL elements in the "group by" clause. + """ + qn = self.quote_name_unless_alias + result = [] + for col in self.group_by: + if isinstance(col, (list, tuple)): + result.append('%s.%s' % (qn(col[0]), qn(col[1]))) + elif hasattr(col, 'as_sql'): + result.append(col.as_sql(qn)) + else: + result.append(str(col)) + return result + + def get_ordering(self): + """ + Returns list representing the SQL elements in the "order by" clause. + Also sets the ordering_aliases attribute on this instance to a list of + extra aliases needed in the select. + + Determining the ordering SQL can change the tables we need to include, + so this should be run *before* get_from_clause(). + """ + if self.extra_order_by: + ordering = self.extra_order_by + elif not self.default_ordering: + ordering = [] + else: + ordering = self.order_by or self.model._meta.ordering + qn = self.quote_name_unless_alias + qn2 = self.connection.ops.quote_name + distinct = self.distinct + select_aliases = self._select_aliases + result = [] + ordering_aliases = [] + if self.standard_ordering: + asc, desc = ORDER_DIR['ASC'] + else: + asc, desc = ORDER_DIR['DESC'] + for field in ordering: + if field == '?': + result.append(self.connection.ops.random_function_sql()) + continue + if isinstance(field, int): + if field < 0: + order = desc + field = -field + else: + order = asc + result.append('%s %s' % (field, order)) + continue + if '.' in field: + # This came in through an extra(order_by=...) addition. Pass it + # on verbatim. + col, order = get_order_dir(field, asc) + table, col = col.split('.', 1) + elt = '%s.%s' % (qn(table), col) + if not distinct or elt in select_aliases: + result.append('%s %s' % (elt, order)) + elif get_order_dir(field)[0] not in self.extra_select: + # 'col' is of the form 'field' or 'field1__field2' or + # '-field1__field2__field', etc. + for table, col, order in self.find_ordering_name(field, + self.model._meta, default_order=asc): + elt = '%s.%s' % (qn(table), qn2(col)) + if distinct and elt not in select_aliases: + ordering_aliases.append(elt) + result.append('%s %s' % (elt, order)) + else: + col, order = get_order_dir(field, asc) + elt = qn(col) + if distinct and elt not in select_aliases: + ordering_aliases.append(elt) + result.append('%s %s' % (elt, order)) + self.ordering_aliases = ordering_aliases + return result + + def find_ordering_name(self, name, opts, alias=None, default_order='ASC', + already_seen=None): + """ + Returns the table alias (the name might be ambiguous, the alias will + not be) and column name for ordering by the given 'name' parameter. + The 'name' is of the form 'field1__field2__...__fieldN'. + """ + name, order = get_order_dir(name, default_order) + pieces = name.split(LOOKUP_SEP) + if not alias: + alias = self.get_initial_alias() + field, target, opts, joins, last = self.setup_joins(pieces, opts, + alias, False) + alias = joins[-1] + col = target.column + if not field.rel: + # To avoid inadvertent trimming of a necessary alias, use the + # refcount to show that we are referencing a non-relation field on + # the model. + self.ref_alias(alias) + + # Must use left outer joins for nullable fields. + for join in joins: + self.promote_alias(join) + + # If we get to this point and the field is a relation to another model, + # append the default ordering for that model. + if field.rel and len(joins) > 1 and opts.ordering: + # Firstly, avoid infinite loops. + if not already_seen: + already_seen = set() + join_tuple = tuple([self.alias_map[j][TABLE_NAME] for j in joins]) + if join_tuple in already_seen: + raise FieldError('Infinite loop caused by ordering.') + already_seen.add(join_tuple) + + results = [] + for item in opts.ordering: + results.extend(self.find_ordering_name(item, opts, alias, + order, already_seen)) + return results + + if alias: + # We have to do the same "final join" optimisation as in + # add_filter, since the final column might not otherwise be part of + # the select set (so we can't order on it). + while 1: + join = self.alias_map[alias] + if col != join[RHS_JOIN_COL]: + break + self.unref_alias(alias) + alias = join[LHS_ALIAS] + col = join[LHS_JOIN_COL] + return [(alias, col, order)] + + def table_alias(self, table_name, create=False): + """ + Returns a table alias for the given table_name and whether this is a + new alias or not. + + If 'create' is true, a new alias is always created. Otherwise, the + most recently created alias for the table (if one exists) is reused. + """ + current = self.table_map.get(table_name) + if not create and current: + alias = current[0] + self.alias_refcount[alias] += 1 + return alias, False + + # Create a new alias for this table. + if current: + alias = '%s%d' % (self.alias_prefix, len(self.alias_map) + 1) + current.append(alias) + else: + # The first occurence of a table uses the table name directly. + alias = table_name + self.table_map[alias] = [alias] + self.alias_refcount[alias] = 1 + #self.alias_map[alias] = None + self.tables.append(alias) + return alias, True + + def ref_alias(self, alias): + """ Increases the reference count for this alias. """ + self.alias_refcount[alias] += 1 + + def unref_alias(self, alias): + """ Decreases the reference count for this alias. """ + self.alias_refcount[alias] -= 1 + + def promote_alias(self, alias, unconditional=False): + """ + Promotes the join type of an alias to an outer join if it's possible + for the join to contain NULL values on the left. If 'unconditional' is + False, the join is only promoted if it is nullable, otherwise it is + always promoted. + + Returns True if the join was promoted. + """ + if ((unconditional or self.alias_map[alias][NULLABLE]) and + self.alias_map[alias] != self.LOUTER): + data = list(self.alias_map[alias]) + data[JOIN_TYPE] = self.LOUTER + self.alias_map[alias] = tuple(data) + return True + return False + + def change_aliases(self, change_map): + """ + Changes the aliases in change_map (which maps old-alias -> new-alias), + relabelling any references to them in select columns and the where + clause. + """ + assert set(change_map.keys()).intersection(set(change_map.values())) == set() + + # 1. Update references in "select" and "where". + self.where.relabel_aliases(change_map) + for pos, col in enumerate(self.select): + if isinstance(col, (list, tuple)): + self.select[pos] = (change_map.get(old_alias, old_alias), col[1]) + else: + col.relabel_aliases(change_map) + + # 2. Rename the alias in the internal table/alias datastructures. + for old_alias, new_alias in change_map.iteritems(): + alias_data = list(self.alias_map[old_alias]) + alias_data[RHS_ALIAS] = new_alias + + t = self.rev_join_map[old_alias] + data = list(self.join_map[t]) + data[data.index(old_alias)] = new_alias + self.join_map[t] = tuple(data) + self.rev_join_map[new_alias] = t + del self.rev_join_map[old_alias] + self.alias_refcount[new_alias] = self.alias_refcount[old_alias] + del self.alias_refcount[old_alias] + self.alias_map[new_alias] = tuple(alias_data) + del self.alias_map[old_alias] + + table_aliases = self.table_map[alias_data[TABLE_NAME]] + for pos, alias in enumerate(table_aliases): + if alias == old_alias: + table_aliases[pos] = new_alias + break + for pos, alias in enumerate(self.tables): + if alias == old_alias: + self.tables[pos] = new_alias + break + + # 3. Update any joins that refer to the old alias. + for alias, data in self.alias_map.iteritems(): + lhs = data[LHS_ALIAS] + if lhs in change_map: + data = list(data) + data[LHS_ALIAS] = change_map[lhs] + self.alias_map[alias] = tuple(data) + + def bump_prefix(self, exceptions=()): + """ + Changes the alias prefix to the next letter in the alphabet and + relabels all the aliases. Even tables that previously had no alias will + get an alias after this call (it's mostly used for nested queries and + the outer query will already be using the non-aliased table name). + + Subclasses who create their own prefix should override this method to + produce a similar result (a new prefix and relabelled aliases). + + The 'exceptions' parameter is a container that holds alias names which + should not be changed. + """ + assert ord(self.alias_prefix) < ord('Z') + self.alias_prefix = chr(ord(self.alias_prefix) + 1) + change_map = {} + prefix = self.alias_prefix + for pos, alias in enumerate(self.tables): + if alias in exceptions: + continue + new_alias = '%s%d' % (prefix, pos) + change_map[alias] = new_alias + self.tables[pos] = new_alias + self.change_aliases(change_map) + + def get_initial_alias(self): + """ + Returns the first alias for this query, after increasing its reference + count. + """ + if self.tables: + alias = self.tables[0] + self.ref_alias(alias) + else: + alias = self.join((None, self.model._meta.db_table, None, None)) + return alias + + def count_active_tables(self): + """ + Returns the number of tables in this query with a non-zero reference + count. + """ + return len([1 for count in self.alias_refcount.itervalues() if count]) + + def join(self, connection, always_create=False, exclusions=(), + promote=False, outer_if_first=False, nullable=False, reuse=None): + """ + Returns an alias for the join in 'connection', either reusing an + existing alias for that join or creating a new one. 'connection' is a + tuple (lhs, table, lhs_col, col) where 'lhs' is either an existing + table alias or a table name. The join correspods to the SQL equivalent + of:: + + lhs.lhs_col = table.col + + If 'always_create' is True and 'reuse' is None, a new alias is always + created, regardless of whether one already exists or not. Otherwise + 'reuse' must be a set and a new join is created unless one of the + aliases in `reuse` can be used. + + If 'exclusions' is specified, it is something satisfying the container + protocol ("foo in exclusions" must work) and specifies a list of + aliases that should not be returned, even if they satisfy the join. + + If 'promote' is True, the join type for the alias will be LOUTER (if + the alias previously existed, the join type will be promoted from INNER + to LOUTER, if necessary). + + If 'outer_if_first' is True and a new join is created, it will have the + LOUTER join type. This is used when joining certain types of querysets + and Q-objects together. + + If 'nullable' is True, the join can potentially involve NULL values and + is a candidate for promotion (to "left outer") when combining querysets. + """ + lhs, table, lhs_col, col = connection + if lhs in self.alias_map: + lhs_table = self.alias_map[lhs][TABLE_NAME] + else: + lhs_table = lhs + + if reuse and always_create and table in self.table_map: + # Convert the 'reuse' to case to be "exclude everything but the + # reusable set, minus exclusions, for this table". + exclusions = set(self.table_map[table]).difference(reuse).union(set(exclusions)) + always_create = False + t_ident = (lhs_table, table, lhs_col, col) + if not always_create: + for alias in self.join_map.get(t_ident, ()): + if alias not in exclusions: + if lhs_table and not self.alias_refcount[self.alias_map[alias][LHS_ALIAS]]: + # The LHS of this join tuple is no longer part of the + # query, so skip this possibility. + continue + self.ref_alias(alias) + if promote: + self.promote_alias(alias) + return alias + + # No reuse is possible, so we need a new alias. + alias, _ = self.table_alias(table, True) + if not lhs: + # Not all tables need to be joined to anything. No join type + # means the later columns are ignored. + join_type = None + elif promote or outer_if_first: + join_type = self.LOUTER + else: + join_type = self.INNER + join = (table, alias, join_type, lhs, lhs_col, col, nullable) + self.alias_map[alias] = join + if t_ident in self.join_map: + self.join_map[t_ident] += (alias,) + else: + self.join_map[t_ident] = (alias,) + self.rev_join_map[alias] = t_ident + return alias + + def fill_related_selections(self, opts=None, root_alias=None, cur_depth=1, + used=None, requested=None, restricted=None, nullable=None, + dupe_set=None): + """ + Fill in the information needed for a select_related query. The current + depth is measured as the number of connections away from the root model + (for example, cur_depth=1 means we are looking at models with direct + connections to the root model). + """ + if not restricted and self.max_depth and cur_depth > self.max_depth: + # We've recursed far enough; bail out. + return + + if not opts: + opts = self.get_meta() + root_alias = self.get_initial_alias() + self.related_select_cols = [] + self.related_select_fields = [] + if not used: + used = set() + if dupe_set is None: + dupe_set = set() + orig_dupe_set = dupe_set + orig_used = used + + # Setup for the case when only particular related fields should be + # included in the related selection. + if requested is None and restricted is not False: + if isinstance(self.select_related, dict): + requested = self.select_related + restricted = True + else: + restricted = False + + for f, model in opts.get_fields_with_model(): + if not select_related_descend(f, restricted, requested): + continue + dupe_set = orig_dupe_set.copy() + used = orig_used.copy() + table = f.rel.to._meta.db_table + if nullable or f.null: + promote = True + else: + promote = False + if model: + int_opts = opts + alias = root_alias + for int_model in opts.get_base_chain(model): + lhs_col = int_opts.parents[int_model].column + dedupe = lhs_col in opts.duplicate_targets + if dedupe: + used.update(self.dupe_avoidance.get(id(opts), lhs_col), + ()) + dupe_set.add((opts, lhs_col)) + int_opts = int_model._meta + alias = self.join((alias, int_opts.db_table, lhs_col, + int_opts.pk.column), exclusions=used, + promote=promote) + for (dupe_opts, dupe_col) in dupe_set: + self.update_dupe_avoidance(dupe_opts, dupe_col, alias) + else: + alias = root_alias + + dedupe = f.column in opts.duplicate_targets + if dupe_set or dedupe: + used.update(self.dupe_avoidance.get((id(opts), f.column), ())) + if dedupe: + dupe_set.add((opts, f.column)) + + alias = self.join((alias, table, f.column, + f.rel.get_related_field().column), exclusions=used, + promote=promote) + used.add(alias) + self.related_select_cols.extend(self.get_default_columns( + start_alias=alias, opts=f.rel.to._meta, as_pairs=True)[0]) + self.related_select_fields.extend(f.rel.to._meta.fields) + if restricted: + next = requested.get(f.name, {}) + else: + next = False + if f.null is not None: + new_nullable = f.null + else: + new_nullable = None + for dupe_opts, dupe_col in dupe_set: + self.update_dupe_avoidance(dupe_opts, dupe_col, alias) + self.fill_related_selections(f.rel.to._meta, alias, cur_depth + 1, + used, next, restricted, new_nullable, dupe_set) + + def add_filter(self, filter_expr, connector=AND, negate=False, trim=False, + can_reuse=None): + """ + Add a single filter to the query. The 'filter_expr' is a pair: + (filter_string, value). E.g. ('name__contains', 'fred') + + If 'negate' is True, this is an exclude() filter. It's important to + note that this method does not negate anything in the where-clause + object when inserting the filter constraints. This is because negated + filters often require multiple calls to add_filter() and the negation + should only happen once. So the caller is responsible for this (the + caller will normally be add_q(), so that as an example). + + If 'trim' is True, we automatically trim the final join group (used + internally when constructing nested queries). + + If 'can_reuse' is a set, we are processing a component of a + multi-component filter (e.g. filter(Q1, Q2)). In this case, 'can_reuse' + will be a set of table aliases that can be reused in this filter, even + if we would otherwise force the creation of new aliases for a join + (needed for nested Q-filters). The set is updated by this method. + """ + arg, value = filter_expr + parts = arg.split(LOOKUP_SEP) + if not parts: + raise FieldError("Cannot parse keyword query %r" % arg) + + # Work out the lookup type and remove it from 'parts', if necessary. + if len(parts) == 1 or parts[-1] not in self.query_terms: + lookup_type = 'exact' + else: + lookup_type = parts.pop() + + # Interpret '__exact=None' as the sql 'is NULL'; otherwise, reject all + # uses of None as a query value. + if value is None: + if lookup_type != 'exact': + raise ValueError("Cannot use None as a query value") + lookup_type = 'isnull' + value = True + elif callable(value): + value = value() + + opts = self.get_meta() + alias = self.get_initial_alias() + allow_many = trim or not negate + + try: + field, target, opts, join_list, last = self.setup_joins(parts, opts, + alias, True, allow_many, can_reuse=can_reuse) + except MultiJoin, e: + self.split_exclude(filter_expr, LOOKUP_SEP.join(parts[:e.level])) + return + final = len(join_list) + penultimate = last.pop() + if penultimate == final: + penultimate = last.pop() + if trim and len(join_list) > 1: + extra = join_list[penultimate:] + join_list = join_list[:penultimate] + final = penultimate + penultimate = last.pop() + col = self.alias_map[extra[0]][LHS_JOIN_COL] + for alias in extra: + self.unref_alias(alias) + else: + col = target.column + alias = join_list[-1] + + while final > 1: + # An optimization: if the final join is against the same column as + # we are comparing against, we can go back one step in the join + # chain and compare against the lhs of the join instead (and then + # repeat the optimization). The result, potentially, involves less + # table joins. + join = self.alias_map[alias] + if col != join[RHS_JOIN_COL]: + break + self.unref_alias(alias) + alias = join[LHS_ALIAS] + col = join[LHS_JOIN_COL] + join_list = join_list[:-1] + final -= 1 + if final == penultimate: + penultimate = last.pop() + + if (lookup_type == 'isnull' and value is True and not negate and + final > 1): + # If the comparison is against NULL, we need to use a left outer + # join when connecting to the previous model. We make that + # adjustment here. We don't do this unless needed as it's less + # efficient at the database level. + self.promote_alias(join_list[penultimate]) + + if connector == OR: + # Some joins may need to be promoted when adding a new filter to a + # disjunction. We walk the list of new joins and where it diverges + # from any previous joins (ref count is 1 in the table list), we + # make the new additions (and any existing ones not used in the new + # join list) an outer join. + join_it = iter(join_list) + table_it = iter(self.tables) + join_it.next(), table_it.next() + table_promote = False + for join in join_it: + table = table_it.next() + if join == table and self.alias_refcount[join] > 1: + continue + join_promote = self.promote_alias(join) + if table != join: + table_promote = self.promote_alias(table) + break + for join in join_it: + if self.promote_alias(join, join_promote): + join_promote = True + for table in table_it: + # Some of these will have been promoted from the join_list, but + # that's harmless. + if self.promote_alias(table, table_promote): + table_promote = True + + self.where.add((alias, col, field, lookup_type, value), connector) + + if negate: + for alias in join_list: + self.promote_alias(alias) + if lookup_type != 'isnull': + if final > 1: + for alias in join_list: + if self.alias_map[alias][JOIN_TYPE] == self.LOUTER: + j_col = self.alias_map[alias][RHS_JOIN_COL] + entry = self.where_class() + entry.add((alias, j_col, None, 'isnull', True), AND) + entry.negate() + self.where.add(entry, AND) + break + elif not (lookup_type == 'in' and not value) and field.null: + # Leaky abstraction artifact: We have to specifically + # exclude the "foo__in=[]" case from this handling, because + # it's short-circuited in the Where class. + entry = self.where_class() + entry.add((alias, col, None, 'isnull', True), AND) + entry.negate() + self.where.add(entry, AND) + + if can_reuse is not None: + can_reuse.update(join_list) + + def add_q(self, q_object, used_aliases=None): + """ + Adds a Q-object to the current filter. + + Can also be used to add anything that has an 'add_to_query()' method. + """ + if used_aliases is None: + used_aliases = self.used_aliases + if hasattr(q_object, 'add_to_query'): + # Complex custom objects are responsible for adding themselves. + q_object.add_to_query(self, used_aliases) + else: + if self.where and q_object.connector != AND and len(q_object) > 1: + self.where.start_subtree(AND) + subtree = True + else: + subtree = False + connector = AND + for child in q_object.children: + if isinstance(child, Node): + self.where.start_subtree(connector) + self.add_q(child, used_aliases) + self.where.end_subtree() + else: + self.add_filter(child, connector, q_object.negated, + can_reuse=used_aliases) + connector = q_object.connector + if q_object.negated: + self.where.negate() + if subtree: + self.where.end_subtree() + if self.filter_is_sticky: + self.used_aliases = used_aliases + + def setup_joins(self, names, opts, alias, dupe_multis, allow_many=True, + allow_explicit_fk=False, can_reuse=None): + """ + Compute the necessary table joins for the passage through the fields + given in 'names'. 'opts' is the Options class for the current model + (which gives the table we are joining to), 'alias' is the alias for the + table we are joining to. If dupe_multis is True, any many-to-many or + many-to-one joins will always create a new alias (necessary for + disjunctive filters). If can_reuse is not None, it's a list of aliases + that can be reused in these joins (nothing else can be reused in this + case). + + Returns the final field involved in the join, the target database + column (used for any 'where' constraint), the final 'opts' value and the + list of tables joined. + """ + joins = [alias] + last = [0] + dupe_set = set() + exclusions = set() + for pos, name in enumerate(names): + try: + exclusions.add(int_alias) + except NameError: + pass + exclusions.add(alias) + last.append(len(joins)) + if name == 'pk': + name = opts.pk.name + + try: + field, model, direct, m2m = opts.get_field_by_name(name) + except FieldDoesNotExist: + for f in opts.fields: + if allow_explicit_fk and name == f.attname: + # XXX: A hack to allow foo_id to work in values() for + # backwards compatibility purposes. If we dropped that + # feature, this could be removed. + field, model, direct, m2m = opts.get_field_by_name(f.name) + break + else: + names = opts.get_all_field_names() + raise FieldError("Cannot resolve keyword %r into field. " + "Choices are: %s" % (name, ", ".join(names))) + + if not allow_many and (m2m or not direct): + for alias in joins: + self.unref_alias(alias) + raise MultiJoin(pos + 1) + if model: + # The field lives on a base class of the current model. + for int_model in opts.get_base_chain(model): + lhs_col = opts.parents[int_model].column + dedupe = lhs_col in opts.duplicate_targets + if dedupe: + exclusions.update(self.dupe_avoidance.get( + (id(opts), lhs_col), ())) + dupe_set.add((opts, lhs_col)) + opts = int_model._meta + alias = self.join((alias, opts.db_table, lhs_col, + opts.pk.column), exclusions=exclusions) + joins.append(alias) + exclusions.add(alias) + for (dupe_opts, dupe_col) in dupe_set: + self.update_dupe_avoidance(dupe_opts, dupe_col, alias) + cached_data = opts._join_cache.get(name) + orig_opts = opts + dupe_col = direct and field.column or field.field.column + dedupe = dupe_col in opts.duplicate_targets + if dupe_set or dedupe: + if dedupe: + dupe_set.add((opts, dupe_col)) + exclusions.update(self.dupe_avoidance.get((id(opts), dupe_col), + ())) + + if direct: + if m2m: + # Many-to-many field defined on the current model. + if cached_data: + (table1, from_col1, to_col1, table2, from_col2, + to_col2, opts, target) = cached_data + else: + table1 = field.m2m_db_table() + from_col1 = opts.pk.column + to_col1 = field.m2m_column_name() + opts = field.rel.to._meta + table2 = opts.db_table + from_col2 = field.m2m_reverse_name() + to_col2 = opts.pk.column + target = opts.pk + orig_opts._join_cache[name] = (table1, from_col1, + to_col1, table2, from_col2, to_col2, opts, + target) + + int_alias = self.join((alias, table1, from_col1, to_col1), + dupe_multis, exclusions, nullable=True, + reuse=can_reuse) + alias = self.join((int_alias, table2, from_col2, to_col2), + dupe_multis, exclusions, nullable=True, + reuse=can_reuse) + joins.extend([int_alias, alias]) + elif field.rel: + # One-to-one or many-to-one field + if cached_data: + (table, from_col, to_col, opts, target) = cached_data + else: + opts = field.rel.to._meta + target = field.rel.get_related_field() + table = opts.db_table + from_col = field.column + to_col = target.column + orig_opts._join_cache[name] = (table, from_col, to_col, + opts, target) + + alias = self.join((alias, table, from_col, to_col), + exclusions=exclusions, nullable=field.null) + joins.append(alias) + else: + # Non-relation fields. + target = field + break + else: + orig_field = field + field = field.field + if m2m: + # Many-to-many field defined on the target model. + if cached_data: + (table1, from_col1, to_col1, table2, from_col2, + to_col2, opts, target) = cached_data + else: + table1 = field.m2m_db_table() + from_col1 = opts.pk.column + to_col1 = field.m2m_reverse_name() + opts = orig_field.opts + table2 = opts.db_table + from_col2 = field.m2m_column_name() + to_col2 = opts.pk.column + target = opts.pk + orig_opts._join_cache[name] = (table1, from_col1, + to_col1, table2, from_col2, to_col2, opts, + target) + + int_alias = self.join((alias, table1, from_col1, to_col1), + dupe_multis, exclusions, nullable=True, + reuse=can_reuse) + alias = self.join((int_alias, table2, from_col2, to_col2), + dupe_multis, exclusions, nullable=True, + reuse=can_reuse) + joins.extend([int_alias, alias]) + else: + # One-to-many field (ForeignKey defined on the target model) + if cached_data: + (table, from_col, to_col, opts, target) = cached_data + else: + local_field = opts.get_field_by_name( + field.rel.field_name)[0] + opts = orig_field.opts + table = opts.db_table + from_col = local_field.column + to_col = field.column + target = opts.pk + orig_opts._join_cache[name] = (table, from_col, to_col, + opts, target) + + alias = self.join((alias, table, from_col, to_col), + dupe_multis, exclusions, nullable=True, + reuse=can_reuse) + joins.append(alias) + + for (dupe_opts, dupe_col) in dupe_set: + try: + self.update_dupe_avoidance(dupe_opts, dupe_col, int_alias) + except NameError: + self.update_dupe_avoidance(dupe_opts, dupe_col, alias) + + if pos != len(names) - 1: + raise FieldError("Join on field %r not permitted." % name) + + return field, target, opts, joins, last + + def update_dupe_avoidance(self, opts, col, alias): + """ + For a column that is one of multiple pointing to the same table, update + the internal data structures to note that this alias shouldn't be used + for those other columns. + """ + ident = id(opts) + for name in opts.duplicate_targets[col]: + try: + self.dupe_avoidance[ident, name].add(alias) + except KeyError: + self.dupe_avoidance[ident, name] = set([alias]) + + def split_exclude(self, filter_expr, prefix): + """ + When doing an exclude against any kind of N-to-many relation, we need + to use a subquery. This method constructs the nested query, given the + original exclude filter (filter_expr) and the portion up to the first + N-to-many relation field. + """ + query = Query(self.model, self.connection) + query.add_filter(filter_expr) + query.set_start(prefix) + query.clear_ordering(True) + self.add_filter(('%s__in' % prefix, query), negate=True, trim=True) + + def set_limits(self, low=None, high=None): + """ + Adjusts the limits on the rows retrieved. We use low/high to set these, + as it makes it more Pythonic to read and write. When the SQL query is + created, they are converted to the appropriate offset and limit values. + + Any limits passed in here are applied relative to the existing + constraints. So low is added to the current low value and both will be + clamped to any existing high value. + """ + if high is not None: + if self.high_mark: + self.high_mark = min(self.high_mark, self.low_mark + high) + else: + self.high_mark = self.low_mark + high + if low is not None: + if self.high_mark: + self.low_mark = min(self.high_mark, self.low_mark + low) + else: + self.low_mark = self.low_mark + low + + def clear_limits(self): + """ + Clears any existing limits. + """ + self.low_mark, self.high_mark = 0, None + + def can_filter(self): + """ + Returns True if adding filters to this instance is still possible. + + Typically, this means no limits or offsets have been put on the results. + """ + return not (self.low_mark or self.high_mark) + + def add_fields(self, field_names, allow_m2m=True): + """ + Adds the given (model) fields to the select set. The field names are + added in the order specified. + """ + alias = self.get_initial_alias() + opts = self.get_meta() + try: + for name in field_names: + field, target, u2, joins, u3 = self.setup_joins( + name.split(LOOKUP_SEP), opts, alias, False, allow_m2m, + True) + final_alias = joins[-1] + col = target.column + if len(joins) > 1: + join = self.alias_map[final_alias] + if col == join[RHS_JOIN_COL]: + self.unref_alias(final_alias) + final_alias = join[LHS_ALIAS] + col = join[LHS_JOIN_COL] + joins = joins[:-1] + promote = False + for join in joins[1:]: + # Only nullable aliases are promoted, so we don't end up + # doing unnecessary left outer joins here. + if self.promote_alias(join, promote): + promote = True + self.select.append((final_alias, col)) + self.select_fields.append(field) + except MultiJoin: + raise FieldError("Invalid field name: '%s'" % name) + except FieldError: + names = opts.get_all_field_names() + self.extra_select.keys() + names.sort() + raise FieldError("Cannot resolve keyword %r into field. " + "Choices are: %s" % (name, ", ".join(names))) + + def add_ordering(self, *ordering): + """ + Adds items from the 'ordering' sequence to the query's "order by" + clause. These items are either field names (not column names) -- + possibly with a direction prefix ('-' or '?') -- or ordinals, + corresponding to column positions in the 'select' list. + + If 'ordering' is empty, all ordering is cleared from the query. + """ + errors = [] + for item in ordering: + if not ORDER_PATTERN.match(item): + errors.append(item) + if errors: + raise FieldError('Invalid order_by arguments: %s' % errors) + if ordering: + self.order_by.extend(ordering) + else: + self.default_ordering = False + + def clear_ordering(self, force_empty=False): + """ + Removes any ordering settings. If 'force_empty' is True, there will be + no ordering in the resulting query (not even the model's default). + """ + self.order_by = [] + self.extra_order_by = () + if force_empty: + self.default_ordering = False + + def add_count_column(self): + """ + Converts the query to do count(...) or count(distinct(pk)) in order to + get its size. + """ + # TODO: When group_by support is added, this needs to be adjusted so + # that it doesn't totally overwrite the select list. + if not self.distinct: + if not self.select: + select = Count() + else: + assert len(self.select) == 1, \ + "Cannot add count col with multiple cols in 'select': %r" % self.select + select = Count(self.select[0]) + else: + opts = self.model._meta + if not self.select: + select = Count((self.join((None, opts.db_table, None, None)), + opts.pk.column), True) + else: + # Because of SQL portability issues, multi-column, distinct + # counts need a sub-query -- see get_count() for details. + assert len(self.select) == 1, \ + "Cannot add count col with multiple cols in 'select'." + select = Count(self.select[0], True) + + # Distinct handling is done in Count(), so don't do it at this + # level. + self.distinct = False + self.select = [select] + self.select_fields = [None] + self.extra_select = {} + + def add_select_related(self, fields): + """ + Sets up the select_related data structure so that we only select + certain related models (as opposed to all models, when + self.select_related=True). + """ + field_dict = {} + for field in fields: + d = field_dict + for part in field.split(LOOKUP_SEP): + d = d.setdefault(part, {}) + self.select_related = field_dict + self.related_select_cols = [] + self.related_select_fields = [] + + def add_extra(self, select, select_params, where, params, tables, order_by): + """ + Adds data to the various extra_* attributes for user-created additions + to the query. + """ + if select: + # We need to pair any placeholder markers in the 'select' + # dictionary with their parameters in 'select_params' so that + # subsequent updates to the select dictionary also adjust the + # parameters appropriately. + select_pairs = SortedDict() + if select_params: + param_iter = iter(select_params) + else: + param_iter = iter([]) + for name, entry in select.items(): + entry = force_unicode(entry) + entry_params = [] + pos = entry.find("%s") + while pos != -1: + entry_params.append(param_iter.next()) + pos = entry.find("%s", pos + 2) + select_pairs[name] = (entry, entry_params) + # This is order preserving, since self.extra_select is a SortedDict. + self.extra_select.update(select_pairs) + if where: + self.extra_where += tuple(where) + if params: + self.extra_params += tuple(params) + if tables: + self.extra_tables += tuple(tables) + if order_by: + self.extra_order_by = order_by + + def trim_extra_select(self, names): + """ + Removes any aliases in the extra_select dictionary that aren't in + 'names'. + + This is needed if we are selecting certain values that don't incldue + all of the extra_select names. + """ + for key in set(self.extra_select).difference(set(names)): + del self.extra_select[key] + + def set_start(self, start): + """ + Sets the table from which to start joining. The start position is + specified by the related attribute from the base model. This will + automatically set to the select column to be the column linked from the + previous table. + + This method is primarily for internal use and the error checking isn't + as friendly as add_filter(). Mostly useful for querying directly + against the join table of many-to-many relation in a subquery. + """ + opts = self.model._meta + alias = self.get_initial_alias() + field, col, opts, joins, last = self.setup_joins( + start.split(LOOKUP_SEP), opts, alias, False) + alias = joins[last[-1]] + self.select = [(alias, self.alias_map[alias][RHS_JOIN_COL])] + self.select_fields = [field] + self.start_meta = opts + + # The call to setup_joins add an extra reference to everything in + # joins. So we need to unref everything once, and everything prior to + # the final join a second time. + for alias in joins: + self.unref_alias(alias) + for alias in joins[:last[-1]]: + self.unref_alias(alias) + + def execute_sql(self, result_type=MULTI): + """ + Run the query against the database and returns the result(s). The + return value is a single data item if result_type is SINGLE, or an + iterator over the results if the result_type is MULTI. + + result_type is either MULTI (use fetchmany() to retrieve all rows), + SINGLE (only retrieve a single row), or None (no results expected, but + the cursor is returned, since it's used by subclasses such as + InsertQuery). + """ + try: + sql, params = self.as_sql() + if not sql: + raise EmptyResultSet + except EmptyResultSet: + if result_type == MULTI: + return empty_iter() + else: + return + + cursor = self.connection.cursor() + cursor.execute(sql, params) + + if not result_type: + return cursor + if result_type == SINGLE: + if self.ordering_aliases: + return cursor.fetchone()[:-len(results.ordering_aliases)] + return cursor.fetchone() + + # The MULTI case. + if self.ordering_aliases: + result = order_modified_iter(cursor, len(self.ordering_aliases), + self.connection.features.empty_fetchmany_value) + else: + result = iter((lambda: cursor.fetchmany(GET_ITERATOR_CHUNK_SIZE)), + self.connection.features.empty_fetchmany_value) + if not self.connection.features.can_use_chunked_reads: + # If we are using non-chunked reads, we return the same data + # structure as normally, but ensure it is all read into memory + # before going any further. + return list(result) + return result + +# Use the backend's custom Query class if it defines one. Otherwise, use the +# default. +if connection.features.uses_custom_query_class: + Query = connection.ops.query_class(Query) + +def get_order_dir(field, default='ASC'): + """ + Returns the field name and direction for an order specification. For + example, '-foo' is returned as ('foo', 'DESC'). + + The 'default' param is used to indicate which way no prefix (or a '+' + prefix) should sort. The '-' prefix always sorts the opposite way. + """ + dirn = ORDER_DIR[default] + if field[0] == '-': + return field[1:], dirn[1] + return field, dirn[0] + +def empty_iter(): + """ + Returns an iterator containing no results. + """ + yield iter([]).next() + +def order_modified_iter(cursor, trim, sentinel): + """ + Yields blocks of rows from a cursor. We use this iterator in the special + case when extra output columns have been added to support ordering + requirements. We must trim those extra columns before anything else can use + the results, since they're only needed to make the SQL valid. + """ + for rows in iter((lambda: cursor.fetchmany(GET_ITERATOR_CHUNK_SIZE)), + sentinel): + yield [r[:-trim] for r in rows] + +def setup_join_cache(sender, **kwargs): + """ + The information needed to join between model fields is something that is + invariant over the life of the model, so we cache it in the model's Options + class, rather than recomputing it all the time. + + This method initialises the (empty) cache when the model is created. + """ + sender._meta._join_cache = {} + +signals.class_prepared.connect(setup_join_cache) + |