[Sqlalchemy-tickets] Issue #3113: Warning for custom insert (MySQL) (zzzeek/sqlalchemy)

[theking-laptop <iss...@bi...>]

New issue 3113: Warning for custom insert (MySQL)
https://bitbucket.org/zzzeek/sqlalchemy/issue/3113/warning-for-custom-insert-mysql

theking-laptop:

I use MySQL as my database backend and I really want to use `INSERT... ON DUPLICATE KEY UPDATE` feature. This is my code:

```
@compiles(Insert, 'mysql')
def suffix_insert(insert, compiler, **kw):
    stmt = compiler.visit_insert(insert, **kw)
    if 'on_duplicate_key_update_cols' in insert.kwargs:
        update_cols = insert.kwargs['on_duplicate_key_update_cols']
        update_cols_length = len(update_cols)
        if update_cols_length > 0:
            stmt += ' ON DUPLICATE KEY UPDATE'
            stmt += " %s=VALUES(%s)" % (update_cols[0], update_cols[0])
            for i in xrange(1, update_cols_length):
                stmt += ",%s=VALUES(%s)" % (update_cols[i], update_cols[i])
    return stmt
```

It works perfectly when I use SqlAlchemy 0.9.1 or below. With higher version, everything is still fine, but I got warning: 
```
lib/python2.7/site-packages/sqlalchemy/sql/dml.py:465: SAWarning: Can't validate argument 'on_duplicate_key_update'; can't locate any SQLAlchemy dialect named 'on'
  self._validate_dialect_kwargs(dialect_kw)
```

How can I workaround this problem?