django/db/models/sql/datastructures.py
"""
Useful auxiliary data structures for query construction. Not useful outside
the SQL domain.
"""
import warnings
from django.core.exceptions import FullResultSet
from django.db.models.sql.constants import INNER, LOUTER
from django.utils.deprecation import RemovedInDjango60Warning
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:
pass
class Join:
"""
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,
filtered_relation=None,
):
# 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.
if hasattr(join_field, "get_joining_fields"):
self.join_fields = join_field.get_joining_fields()
self.join_cols = tuple(
(lhs_field.column, rhs_field.column)
for lhs_field, rhs_field in self.join_fields
)
else:
warnings.warn(
"The usage of get_joining_columns() in Join is deprecated. Implement "
"get_joining_fields() instead.",
RemovedInDjango60Warning,
)
self.join_fields = None
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
self.filtered_relation = filtered_relation
def as_sql(self, compiler, connection):
"""
Generate 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.
# RemovedInDjango60Warning: when the depraction ends, replace with:
# for lhs, rhs in self.join_field:
join_fields = self.join_fields or self.join_cols
for lhs, rhs in join_fields:
if isinstance(lhs, str):
# RemovedInDjango60Warning: when the depraction ends, remove
# the branch for strings.
lhs_full_name = "%s.%s" % (qn(self.parent_alias), qn2(lhs))
rhs_full_name = "%s.%s" % (qn(self.table_alias), qn2(rhs))
else:
lhs, rhs = connection.ops.prepare_join_on_clause(
self.parent_alias, lhs, self.table_alias, rhs
)
lhs_sql, lhs_params = compiler.compile(lhs)
lhs_full_name = lhs_sql % lhs_params
rhs_sql, rhs_params = compiler.compile(rhs)
rhs_full_name = rhs_sql % rhs_params
join_conditions.append(f"{lhs_full_name} = {rhs_full_name}")
# Add a single condition inside parentheses for whatever
# get_extra_restriction() returns.
extra_cond = self.join_field.get_extra_restriction(
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 self.filtered_relation:
try:
extra_sql, extra_params = compiler.compile(self.filtered_relation)
except FullResultSet:
pass
else:
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)
if self.filtered_relation is not None:
filtered_relation = self.filtered_relation.relabeled_clone(change_map)
else:
filtered_relation = None
return self.__class__(
self.table_name,
new_parent_alias,
new_table_alias,
self.join_type,
self.join_field,
self.nullable,
filtered_relation=filtered_relation,
)
@property
def identity(self):
return (
self.__class__,
self.table_name,
self.parent_alias,
self.join_field,
self.filtered_relation,
)
def __eq__(self, other):
if not isinstance(other, Join):
return NotImplemented
return self.identity == other.identity
def __hash__(self):
return hash(self.identity)
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:
"""
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
filtered_relation = 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)
)
@property
def identity(self):
return self.__class__, self.table_name, self.table_alias
def __eq__(self, other):
if not isinstance(other, BaseTable):
return NotImplemented
return self.identity == other.identity
def __hash__(self):
return hash(self.identity)