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"""
Useful auxiliary data structures for query construction. Not useful outside
the SQL domain.
"""
from django.db.models.sql.constants import INNER, LOUTER
class EmptyResultSet(Exception):
pass
class MultiJoin(Exception):
"""
Used by join construction code to indicate the point at which a
multi-valued join was attempted (if the caller wants to treat that
exceptionally).
"""
def __init__(self, names_pos, path_with_names):
self.level = names_pos
# The path travelled, this includes the path to the multijoin.
self.names_with_path = path_with_names
class Empty(object):
pass
class Join(object):
"""
Used by sql.Query and sql.SQLCompiler to generate JOIN clauses into the
FROM entry. For example, the SQL generated could be
LEFT OUTER JOIN "sometable" T1 ON ("othertable"."sometable_id" = "sometable"."id")
This class is primarily used in Query.alias_map. All entries in alias_map
must be Join compatible by providing the following attributes and methods:
- table_name (string)
- table_alias (possible alias for the table, can be None)
- join_type (can be None for those entries that aren't joined from
anything)
- parent_alias (which table is this join's parent, can be None similarly
to join_type)
- as_sql()
- relabeled_clone()
"""
def __init__(self, table_name, parent_alias, table_alias, join_type,
join_field, nullable):
# Join table
self.table_name = table_name
self.parent_alias = parent_alias
# Note: table_alias is not necessarily known at instantiation time.
self.table_alias = table_alias
# LOUTER or INNER
self.join_type = join_type
# A list of 2-tuples to use in the ON clause of the JOIN.
# Each 2-tuple will create one join condition in the ON clause.
self.join_cols = join_field.get_joining_columns()
# Along which field (or ForeignObjectRel in the reverse join case)
self.join_field = join_field
# Is this join nullabled?
self.nullable = nullable
def as_sql(self, compiler, connection):
"""
Generates the full
LEFT OUTER JOIN sometable ON sometable.somecol = othertable.othercol, params
clause for this join.
"""
join_conditions = []
params = []
qn = compiler.quote_name_unless_alias
qn2 = connection.ops.quote_name
# Add a join condition for each pair of joining columns.
for index, (lhs_col, rhs_col) in enumerate(self.join_cols):
join_conditions.append('%s.%s = %s.%s' % (
qn(self.parent_alias),
qn2(lhs_col),
qn(self.table_alias),
qn2(rhs_col),
))
# Add a single condition inside parentheses for whatever
# get_extra_restriction() returns.
extra_cond = self.join_field.get_extra_restriction(
compiler.query.where_class, self.table_alias, self.parent_alias)
if extra_cond:
extra_sql, extra_params = compiler.compile(extra_cond)
join_conditions.append('(%s)' % extra_sql)
params.extend(extra_params)
if not join_conditions:
# This might be a rel on the other end of an actual declared field.
declared_field = getattr(self.join_field, 'field', self.join_field)
raise ValueError(
"Join generated an empty ON clause. %s did not yield either "
"joining columns or extra restrictions." % declared_field.__class__
)
on_clause_sql = ' AND '.join(join_conditions)
alias_str = '' if self.table_alias == self.table_name else (' %s' % self.table_alias)
sql = '%s %s%s ON (%s)' % (self.join_type, qn(self.table_name), alias_str, on_clause_sql)
return sql, params
def relabeled_clone(self, change_map):
new_parent_alias = change_map.get(self.parent_alias, self.parent_alias)
new_table_alias = change_map.get(self.table_alias, self.table_alias)
return self.__class__(
self.table_name, new_parent_alias, new_table_alias, self.join_type,
self.join_field, self.nullable)
def __eq__(self, other):
if isinstance(other, self.__class__):
return (
self.table_name == other.table_name and
self.parent_alias == other.parent_alias and
self.join_field == other.join_field
)
return False
def demote(self):
new = self.relabeled_clone({})
new.join_type = INNER
return new
def promote(self):
new = self.relabeled_clone({})
new.join_type = LOUTER
return new
class BaseTable(object):
"""
The BaseTable class is used for base table references in FROM clause. For
example, the SQL "foo" in
SELECT * FROM "foo" WHERE somecond
could be generated by this class.
"""
join_type = None
parent_alias = None
def __init__(self, table_name, alias):
self.table_name = table_name
self.table_alias = alias
def as_sql(self, compiler, connection):
alias_str = '' if self.table_alias == self.table_name else (' %s' % self.table_alias)
base_sql = compiler.quote_name_unless_alias(self.table_name)
return base_sql + alias_str, []
def relabeled_clone(self, change_map):
return self.__class__(self.table_name, change_map.get(self.table_alias, self.table_alias))
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