How to compile an INSERT ... ON DUPLICATE KEY UPDATE with SQL Alchemy with support for a bulk insert.

upsert.py

#!/usr/bin/env python
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"""
This module provides an "Upsert" statement for SQL Alchemy which uses 
ON DUPLICATE KEY UPDATE to implement the insert or update semantics. It
supports doing a bulk insert.
"""

import sqlalchemy as sa
from sqlalchemy.ext.compiler import compiles
import sqlalchemy.sql.expression as expr


class Upsert(expr.Insert):
    pass


@compiles(Upsert, "mysql")
def compile_upsert(insert_stmt, compiler, **kwargs):
    if insert_stmt._has_multi_parameters:
        keys = insert_stmt.parameters[0].keys()
    else:
        keys = insert_stmt.parameters.keys()
    pk = insert_stmt.table.primary_key
    auto = None
    if (len(pk.columns) == 1 and
            isinstance(pk.columns.values()[0].type, sa.Integer) and
            pk.columns.values()[0].autoincrement):
        auto = pk.columns.keys()[0]
        if auto in keys:
            keys.remove(auto)
    insert = compiler.visit_insert(insert_stmt, **kwargs)
    ondup = 'ON DUPLICATE KEY UPDATE'
    updates = ', '.join(
        '%s = VALUES(%s)' % (c.name, c.name)
        for c in insert_stmt.table.columns
        if c.name in keys
    )
    if auto is not None:
        last_id = '%s = LAST_INSERT_ID(%s)' % (auto, auto)
        if updates:
            updates = ', '.join((last_id, updates))
        else:
            updates = last_id
    upsert = ' '.join((insert, ondup, updates))
    return upsert