app/django/db/models/sql/where.py
author Pawel Solyga <Pawel.Solyga@gmail.com>
Tue, 14 Oct 2008 16:00:59 +0000
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Load ../vendor/django into trunk/app/django.
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"""
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Code to manage the creation and SQL rendering of 'where' constraints.
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"""
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import datetime
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from django.utils import tree
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from django.db import connection
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from django.db.models.fields import Field
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from django.db.models.query_utils import QueryWrapper
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from datastructures import EmptyResultSet, FullResultSet
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# Connection types
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AND = 'AND'
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OR = 'OR'
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class WhereNode(tree.Node):
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    """
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    Used to represent the SQL where-clause.
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    The class is tied to the Query class that created it (in order to create
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    the correct SQL).
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    The children in this tree are usually either Q-like objects or lists of
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    [table_alias, field_name, db_type, lookup_type, value_annotation,
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    params]. However, a child could also be any class with as_sql() and
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    relabel_aliases() methods.
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    """
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    default = AND
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    def add(self, data, connector):
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        """
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        Add a node to the where-tree. If the data is a list or tuple, it is
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        expected to be of the form (alias, col_name, field_obj, lookup_type,
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        value), which is then slightly munged before being stored (to avoid
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        storing any reference to field objects). Otherwise, the 'data' is
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        stored unchanged and can be anything with an 'as_sql()' method.
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        """
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        # Because of circular imports, we need to import this here.
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        from django.db.models.base import ObjectDoesNotExist
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        if not isinstance(data, (list, tuple)):
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            super(WhereNode, self).add(data, connector)
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            return
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        alias, col, field, lookup_type, value = data
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        try:
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            if field:
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                params = field.get_db_prep_lookup(lookup_type, value)
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                db_type = field.db_type()
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            else:
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                # This is possible when we add a comparison to NULL sometimes
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                # (we don't really need to waste time looking up the associated
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                # field object).
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                params = Field().get_db_prep_lookup(lookup_type, value)
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                db_type = None
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        except ObjectDoesNotExist:
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            # This can happen when trying to insert a reference to a null pk.
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            # We break out of the normal path and indicate there's nothing to
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            # match.
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            super(WhereNode, self).add(NothingNode(), connector)
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            return
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        if isinstance(value, datetime.datetime):
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            annotation = datetime.datetime
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        else:
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            annotation = bool(value)
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        super(WhereNode, self).add((alias, col, db_type, lookup_type,
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                annotation, params), connector)
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    def as_sql(self, qn=None):
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        """
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        Returns the SQL version of the where clause and the value to be
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        substituted in. Returns None, None if this node is empty.
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        If 'node' is provided, that is the root of the SQL generation
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        (generally not needed except by the internal implementation for
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        recursion).
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        """
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        if not qn:
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            qn = connection.ops.quote_name
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        if not self.children:
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            return None, []
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        result = []
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        result_params = []
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        empty = True
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        for child in self.children:
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            try:
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                if hasattr(child, 'as_sql'):
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                    sql, params = child.as_sql(qn=qn)
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                else:
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                    # A leaf node in the tree.
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                    sql, params = self.make_atom(child, qn)
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            except EmptyResultSet:
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                if self.connector == AND and not self.negated:
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                    # We can bail out early in this particular case (only).
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                    raise
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                elif self.negated:
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                    empty = False
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                continue
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            except FullResultSet:
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                if self.connector == OR:
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                    if self.negated:
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                        empty = True
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                        break
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                    # We match everything. No need for any constraints.
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                    return '', []
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                if self.negated:
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                    empty = True
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                continue
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            empty = False
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            if sql:
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                result.append(sql)
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                result_params.extend(params)
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        if empty:
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            raise EmptyResultSet
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        conn = ' %s ' % self.connector
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        sql_string = conn.join(result)
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        if sql_string:
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            if self.negated:
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                sql_string = 'NOT (%s)' % sql_string
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            elif len(self.children) != 1:
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                sql_string = '(%s)' % sql_string
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        return sql_string, result_params
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    def make_atom(self, child, qn):
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        """
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        Turn a tuple (table_alias, column_name, db_type, lookup_type,
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        value_annot, params) into valid SQL.
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        Returns the string for the SQL fragment and the parameters to use for
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        it.
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        """
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        table_alias, name, db_type, lookup_type, value_annot, params = child
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        if table_alias:
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            lhs = '%s.%s' % (qn(table_alias), qn(name))
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        else:
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            lhs = qn(name)
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        field_sql = connection.ops.field_cast_sql(db_type) % lhs
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        if value_annot is datetime.datetime:
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            cast_sql = connection.ops.datetime_cast_sql()
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        else:
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            cast_sql = '%s'
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        if isinstance(params, QueryWrapper):
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            extra, params = params.data
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        else:
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            extra = ''
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        if lookup_type in connection.operators:
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            format = "%s %%s %s" % (connection.ops.lookup_cast(lookup_type),
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                    extra)
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            return (format % (field_sql,
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                    connection.operators[lookup_type] % cast_sql), params)
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        if lookup_type == 'in':
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            if not value_annot:
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                raise EmptyResultSet
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            if extra:
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                return ('%s IN %s' % (field_sql, extra), params)
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            return ('%s IN (%s)' % (field_sql, ', '.join(['%s'] * len(params))),
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                    params)
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        elif lookup_type in ('range', 'year'):
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            return ('%s BETWEEN %%s and %%s' % field_sql, params)
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        elif lookup_type in ('month', 'day'):
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            return ('%s = %%s' % connection.ops.date_extract_sql(lookup_type,
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                    field_sql), params)
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        elif lookup_type == 'isnull':
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            return ('%s IS %sNULL' % (field_sql,
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                (not value_annot and 'NOT ' or '')), ())
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        elif lookup_type == 'search':
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            return (connection.ops.fulltext_search_sql(field_sql), params)
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        elif lookup_type in ('regex', 'iregex'):
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            return connection.ops.regex_lookup(lookup_type) % (field_sql, cast_sql), params
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        raise TypeError('Invalid lookup_type: %r' % lookup_type)
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    def relabel_aliases(self, change_map, node=None):
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        """
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        Relabels the alias values of any children. 'change_map' is a dictionary
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        mapping old (current) alias values to the new values.
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        """
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        if not node:
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            node = self
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        for pos, child in enumerate(node.children):
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            if hasattr(child, 'relabel_aliases'):
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                child.relabel_aliases(change_map)
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            elif isinstance(child, tree.Node):
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                self.relabel_aliases(change_map, child)
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            else:
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                if child[0] in change_map:
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                    node.children[pos] = (change_map[child[0]],) + child[1:]
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class EverythingNode(object):
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    """
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    A node that matches everything.
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    """
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    def as_sql(self, qn=None):
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        raise FullResultSet
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    def relabel_aliases(self, change_map, node=None):
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        return
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class NothingNode(object):
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    """
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    A node that matches nothing.
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    """
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    def as_sql(self, qn=None):
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        raise EmptyResultSet
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    def relabel_aliases(self, change_map, node=None):
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        return
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   213