221 lines
7.0 KiB
Python
221 lines
7.0 KiB
Python
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"""
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Useful auxiliary data structures for query construction. Not useful outside
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the SQL domain.
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"""
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from django.db.models.sql.constants import INNER, LOUTER
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class MultiJoin(Exception):
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"""
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Used by join construction code to indicate the point at which a
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multi-valued join was attempted (if the caller wants to treat that
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exceptionally).
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"""
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def __init__(self, names_pos, path_with_names):
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self.level = names_pos
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# The path travelled, this includes the path to the multijoin.
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self.names_with_path = path_with_names
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class Empty:
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pass
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class Join:
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"""
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Used by sql.Query and sql.SQLCompiler to generate JOIN clauses into the
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FROM entry. For example, the SQL generated could be
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LEFT OUTER JOIN "sometable" T1
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ON ("othertable"."sometable_id" = "sometable"."id")
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This class is primarily used in Query.alias_map. All entries in alias_map
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must be Join compatible by providing the following attributes and methods:
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- table_name (string)
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- table_alias (possible alias for the table, can be None)
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- join_type (can be None for those entries that aren't joined from
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anything)
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- parent_alias (which table is this join's parent, can be None similarly
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to join_type)
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- as_sql()
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- relabeled_clone()
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"""
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def __init__(
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self,
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table_name,
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parent_alias,
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table_alias,
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join_type,
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join_field,
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nullable,
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filtered_relation=None,
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):
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# Join table
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self.table_name = table_name
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self.parent_alias = parent_alias
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# Note: table_alias is not necessarily known at instantiation time.
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self.table_alias = table_alias
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# LOUTER or INNER
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self.join_type = join_type
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# A list of 2-tuples to use in the ON clause of the JOIN.
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# Each 2-tuple will create one join condition in the ON clause.
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self.join_cols = join_field.get_joining_columns()
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# Along which field (or ForeignObjectRel in the reverse join case)
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self.join_field = join_field
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# Is this join nullabled?
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self.nullable = nullable
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self.filtered_relation = filtered_relation
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def as_sql(self, compiler, connection):
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"""
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Generate the full
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LEFT OUTER JOIN sometable ON sometable.somecol = othertable.othercol, params
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clause for this join.
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"""
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join_conditions = []
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params = []
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qn = compiler.quote_name_unless_alias
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qn2 = connection.ops.quote_name
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# Add a join condition for each pair of joining columns.
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for lhs_col, rhs_col in self.join_cols:
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join_conditions.append(
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"%s.%s = %s.%s"
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% (
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qn(self.parent_alias),
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qn2(lhs_col),
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qn(self.table_alias),
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qn2(rhs_col),
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)
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)
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# Add a single condition inside parentheses for whatever
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# get_extra_restriction() returns.
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extra_cond = self.join_field.get_extra_restriction(
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self.table_alias, self.parent_alias
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)
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if extra_cond:
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extra_sql, extra_params = compiler.compile(extra_cond)
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join_conditions.append("(%s)" % extra_sql)
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params.extend(extra_params)
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if self.filtered_relation:
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extra_sql, extra_params = compiler.compile(self.filtered_relation)
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if extra_sql:
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join_conditions.append("(%s)" % extra_sql)
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params.extend(extra_params)
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if not join_conditions:
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# This might be a rel on the other end of an actual declared field.
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declared_field = getattr(self.join_field, "field", self.join_field)
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raise ValueError(
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"Join generated an empty ON clause. %s did not yield either "
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"joining columns or extra restrictions." % declared_field.__class__
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)
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on_clause_sql = " AND ".join(join_conditions)
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alias_str = (
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"" if self.table_alias == self.table_name else (" %s" % self.table_alias)
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)
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sql = "%s %s%s ON (%s)" % (
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self.join_type,
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qn(self.table_name),
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alias_str,
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on_clause_sql,
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)
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return sql, params
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def relabeled_clone(self, change_map):
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new_parent_alias = change_map.get(self.parent_alias, self.parent_alias)
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new_table_alias = change_map.get(self.table_alias, self.table_alias)
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if self.filtered_relation is not None:
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filtered_relation = self.filtered_relation.clone()
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filtered_relation.path = [
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change_map.get(p, p) for p in self.filtered_relation.path
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]
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else:
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filtered_relation = None
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return self.__class__(
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self.table_name,
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new_parent_alias,
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new_table_alias,
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self.join_type,
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self.join_field,
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self.nullable,
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filtered_relation=filtered_relation,
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)
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@property
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def identity(self):
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return (
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self.__class__,
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self.table_name,
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self.parent_alias,
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self.join_field,
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self.filtered_relation,
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)
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def __eq__(self, other):
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if not isinstance(other, Join):
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return NotImplemented
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return self.identity == other.identity
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def __hash__(self):
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return hash(self.identity)
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def equals(self, other):
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# Ignore filtered_relation in equality check.
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return self.identity[:-1] == other.identity[:-1]
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def demote(self):
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new = self.relabeled_clone({})
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new.join_type = INNER
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return new
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def promote(self):
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new = self.relabeled_clone({})
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new.join_type = LOUTER
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return new
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class BaseTable:
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"""
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The BaseTable class is used for base table references in FROM clause. For
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example, the SQL "foo" in
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SELECT * FROM "foo" WHERE somecond
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could be generated by this class.
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"""
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join_type = None
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parent_alias = None
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filtered_relation = None
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def __init__(self, table_name, alias):
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self.table_name = table_name
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self.table_alias = alias
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def as_sql(self, compiler, connection):
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alias_str = (
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"" if self.table_alias == self.table_name else (" %s" % self.table_alias)
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)
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base_sql = compiler.quote_name_unless_alias(self.table_name)
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return base_sql + alias_str, []
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def relabeled_clone(self, change_map):
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return self.__class__(
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self.table_name, change_map.get(self.table_alias, self.table_alias)
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)
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@property
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def identity(self):
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return self.__class__, self.table_name, self.table_alias
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def __eq__(self, other):
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if not isinstance(other, BaseTable):
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return NotImplemented
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return self.identity == other.identity
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def __hash__(self):
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return hash(self.identity)
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def equals(self, other):
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return self.identity == other.identity
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