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venv/Lib/site-packages/django/db/models/sql/datastructures.py

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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 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.
+        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.
+        for lhs_col, rhs_col in 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(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:
+            extra_sql, extra_params = compiler.compile(self.filtered_relation)
+            if extra_sql:
+                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.clone()
+            filtered_relation.path = [change_map.get(p, p) for p in self.filtered_relation.path]
+        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 equals(self, other):
+        # Ignore filtered_relation in equality check.
+        return self.identity[:-1] == other.identity[:-1]
+
+    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)
+
+    def equals(self, other):
+        return self.identity == other.identity