The general idea is great though you probably want to use the @compiles
decorator to link the compile function to the expression element, since that's
the API point of extension - that would remove the need for the _compiler()
call:
http://www.sqlalchemy.org/docs/core/compiler.html?highlight=compiles
You probably don't need the _copy_internals() call either since
insert/update/delete expressions aren't generally used with clause adaption
(for a description of what that's all about, see
http://techspot.zzzeek.org/2008/01/23/expression-transformations/ ).
On Dec 22, 2010, at 8:51 AM, Tarek Ziadé wrote:
Hello,
I need to add order_by, limit and offset support to Delete objects for
MySQL. Here's what I've done so far, which works. See the long paste
below, I use delete() on my tables.
I would like to know if this is the right way to do things, or if I am
missing something. I am currently using 0.6.x
Thanks !
Tarek
from sqlalchemy.sql.expression import _generative, Delete, _clone, ClauseList
from sqlalchemy import util
from sqlalchemy.sql.compiler import SQLCompiler
class CustomCompiler(SQLCompiler):
def visit_delete(self, delete_stmt):
self.stack.append({'from': set([delete_stmt.table])})
self.isdelete = True
text = DELETE FROM + self.preparer.format_table(delete_stmt.table)
if delete_stmt._returning:
self.returning = delete_stmt._returning
if self.returning_precedes_values:
text += + self.returning_clause(delete_stmt,
delete_stmt._returning)
if delete_stmt._whereclause is not None:
text += WHERE + self.process(delete_stmt._whereclause)
if len(delete_stmt._order_by_clause) 0:
text += ORDER BY + self.process(delete_stmt._order_by_clause)
if delete_stmt._limit is not None or delete_stmt._offset is not None:
text += self.limit_clause(delete_stmt)
if self.returning and not self.returning_precedes_values:
text += + self.returning_clause(delete_stmt,
delete_stmt._returning)
self.stack.pop(-1)
return text
class DeleteOrderBy(Delete):
def __init__(self, table, whereclause, bind=None, returning=None,
order_by=None, limit=None, offset=None, **kwargs):
Delete.__init__(self, table, whereclause, bind, returning, **kwargs)
self._order_by_clause = ClauseList(*util.to_list(order_by) or [])
self._limit = limit
self._offset = offset
@_generative
def order_by(self, *clauses):
self.append_order_by(*clauses)
def append_order_by(self, *clauses):
if len(clauses) == 1 and clauses[0] is None:
self._order_by_clause = ClauseList()
else:
if getattr(self, '_order_by_clause', None) is not None:
clauses = list(self._order_by_clause) + list(clauses)
self._order_by_clause = ClauseList(*clauses)
@_generative
def limit(self, limit):
self._limit = limit
@_generative
def offset(self, offset):
self._offset = offset
def _copy_internals(self, clone=_clone):
self._whereclause = clone(self._whereclause)
for attr in ('_order_by_clause',):
if getattr(self, attr) is not None:
setattr(self, attr, clone(getattr(self, attr)))
def get_children(self, column_collections=True, **kwargs):
children = Delete.get_children(column_collections, **kwargs)
return children + [self._order_by_clause]
def _compiler(self, dialect, **kw):
return CustomCompiler(dialect, self, **kw)
def delete(table, whereclause = None, **kwargs):
return DeleteOrderBy(table, whereclause, **kwargs)
--
Tarek Ziadé | http://ziade.org
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