217 lines
7.6 KiB
Python
217 lines
7.6 KiB
Python
"""
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Code to manage the creation and SQL rendering of 'where' constraints.
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"""
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from django.core.exceptions import EmptyResultSet
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from django.utils import tree
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from django.utils.functional import cached_property
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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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A child is usually an expression producing boolean values. Most likely the
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expression is a Lookup instance.
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However, a child could also be any class with as_sql() and either
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relabeled_clone() method or relabel_aliases() and clone() methods and
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contains_aggregate attribute.
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"""
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default = AND
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def split_having(self, negated=False):
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"""
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Returns two possibly None nodes: one for those parts of self that
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should be included in the WHERE clause and one for those parts of
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self that must be included in the HAVING clause.
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"""
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if not self.contains_aggregate:
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return self, None
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in_negated = negated ^ self.negated
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# If the effective connector is OR and this node contains an aggregate,
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# then we need to push the whole branch to HAVING clause.
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may_need_split = (
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(in_negated and self.connector == AND) or
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(not in_negated and self.connector == OR))
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if may_need_split and self.contains_aggregate:
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return None, self
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where_parts = []
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having_parts = []
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for c in self.children:
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if hasattr(c, 'split_having'):
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where_part, having_part = c.split_having(in_negated)
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if where_part is not None:
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where_parts.append(where_part)
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if having_part is not None:
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having_parts.append(having_part)
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elif c.contains_aggregate:
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having_parts.append(c)
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else:
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where_parts.append(c)
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having_node = self.__class__(having_parts, self.connector, self.negated) if having_parts else None
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where_node = self.__class__(where_parts, self.connector, self.negated) if where_parts else None
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return where_node, having_node
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def as_sql(self, compiler, connection):
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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 '', [] if this node matches everything,
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None, [] if this node is empty, and raises EmptyResultSet if this
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node can't match anything.
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"""
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result = []
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result_params = []
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if self.connector == AND:
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full_needed, empty_needed = len(self.children), 1
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else:
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full_needed, empty_needed = 1, len(self.children)
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for child in self.children:
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try:
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sql, params = compiler.compile(child)
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except EmptyResultSet:
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empty_needed -= 1
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else:
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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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else:
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full_needed -= 1
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# Check if this node matches nothing or everything.
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# First check the amount of full nodes and empty nodes
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# to make this node empty/full.
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# Now, check if this node is full/empty using the
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# counts.
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if empty_needed == 0:
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if self.negated:
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return '', []
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else:
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raise EmptyResultSet
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if full_needed == 0:
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if self.negated:
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raise EmptyResultSet
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else:
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return '', []
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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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# Some backends (Oracle at least) need parentheses
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# around the inner SQL in the negated case, even if the
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# inner SQL contains just a single expression.
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sql_string = 'NOT (%s)' % sql_string
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elif len(result) > 1:
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sql_string = '(%s)' % sql_string
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return sql_string, result_params
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def get_group_by_cols(self):
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cols = []
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for child in self.children:
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cols.extend(child.get_group_by_cols())
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return cols
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def relabel_aliases(self, change_map):
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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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for pos, child in enumerate(self.children):
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if hasattr(child, 'relabel_aliases'):
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# For example another WhereNode
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child.relabel_aliases(change_map)
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elif hasattr(child, 'relabeled_clone'):
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self.children[pos] = child.relabeled_clone(change_map)
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def clone(self):
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"""
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Creates a clone of the tree. Must only be called on root nodes (nodes
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with empty subtree_parents). Childs must be either (Contraint, lookup,
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value) tuples, or objects supporting .clone().
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"""
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clone = self.__class__._new_instance(
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children=[], connector=self.connector, negated=self.negated)
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for child in self.children:
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if hasattr(child, 'clone'):
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clone.children.append(child.clone())
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else:
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clone.children.append(child)
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return clone
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def relabeled_clone(self, change_map):
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clone = self.clone()
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clone.relabel_aliases(change_map)
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return clone
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@classmethod
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def _contains_aggregate(cls, obj):
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if isinstance(obj, tree.Node):
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return any(cls._contains_aggregate(c) for c in obj.children)
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return obj.contains_aggregate
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@cached_property
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def contains_aggregate(self):
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return self._contains_aggregate(self)
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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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contains_aggregate = False
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def as_sql(self, compiler=None, connection=None):
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raise EmptyResultSet
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class ExtraWhere(object):
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# The contents are a black box - assume no aggregates are used.
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contains_aggregate = False
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def __init__(self, sqls, params):
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self.sqls = sqls
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self.params = params
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def as_sql(self, compiler=None, connection=None):
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sqls = ["(%s)" % sql for sql in self.sqls]
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return " AND ".join(sqls), list(self.params or ())
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class SubqueryConstraint(object):
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# Even if aggregates would be used in a subquery, the outer query isn't
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# interested about those.
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contains_aggregate = False
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def __init__(self, alias, columns, targets, query_object):
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self.alias = alias
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self.columns = columns
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self.targets = targets
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self.query_object = query_object
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def as_sql(self, compiler, connection):
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query = self.query_object
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# QuerySet was sent
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if hasattr(query, 'values'):
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if query._db and connection.alias != query._db:
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raise ValueError("Can't do subqueries with queries on different DBs.")
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# Do not override already existing values.
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if query._fields is None:
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query = query.values(*self.targets)
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else:
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query = query._clone()
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query = query.query
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if query.can_filter():
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# If there is no slicing in use, then we can safely drop all ordering
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query.clear_ordering(True)
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query_compiler = query.get_compiler(connection=connection)
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return query_compiler.as_subquery_condition(self.alias, self.columns, compiler)
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