update/delete google appengine entity by sql like syntax

appengine_sql.py

#! /usr/bin/env python
# coding: utf-8
#
# update/delete google appengine entity by sql like syntax...
#
# sample: 
#   - update
#     noresult('update MyModel set name = \'hoge\', age = 10') # update all entities
#     noresult('update MyModel set name = \'fuga\' where id = 10') # update entities which is specified in where clause
#     * unavailable - multiple inequality filter property
#     noresult('udpate MyModel set name = \'fugo\' where rank > 10')
#   - delete
#     noresult('delete from MyModel') # delete all entities
#     noresult('delete from MyModel where age < 10') # delete entities which is specified in where clause 
#
#
#
from google.appengine.ext import db

# ref: http://code.google.com/intl/ja/appengine/docs/python/datastore/overview.html
MAX_BATCH_PUT_OR_DELETE = 500



def noresult(stmt):
    lst = stmt.split()
 
    op = lst[0]
    model = lst[1] if op == 'update' else lst[2]
 
    def build_query_delete():
        q = 'select * from %s' % model
        if stmt.find('where') >= 0:
            q = q + ' ' + stmt[stmt.index('where'):]
        return db.GqlQuery(q)

    def build_query_update(key):
        q = 'select * from ' + model
        b = not (key is None)
        c = stmt.find('where') >= 0
        if b or c:
            q += ' where '
            conds = []
            if b: conds.append(' __key__ > :1 ')
            if c: conds.append(stmt[stmt.index('where')+5:])
            q += ' AND '.join(conds)
        q += ' order by __key__'
        args = [q]
        if b: args.append(key)
        return db.GqlQuery(*args)
 
    def update(bq, ulist):
        key = None
        q = bq(key)
        while True:
            lst = q.fetch(MAX_BATCH_PUT_OR_DELETE)
            if len(lst) == 0:
                break
            for model in lst:
                for prop,value in ulist:
                    setattr(model, prop, value)
            db.put(lst)
            key = lst[-1].key()
            q = bq(key)
    
    def delete(bq):
        q = bq()
        while True:
            lst = q.fetch(MAX_BATCH_PUT_OR_DELETE)
            if len(lst) == 0:
                break
            db.delete(lst)
            q = bq()

    if op == 'update':
        fieldlist = stmt[stmt.index('set')+3:]
        if fieldlist.find('where') >= 0:
            fieldlist = fieldlist[:fieldlist.index('where')]
        fieldlist = fieldlist.split(',')
 
        def convert(item):
            index = item.index('=')
            prop = item[:index].strip()
            value = item[index+1:].strip()
            try:
                value = eval(value)
            except:
                pass
            return prop,value
        updatelist = map(convert, fieldlist)
        update(build_query_update, updatelist)
 
    elif op == 'delete':
        delete(build_query_delete)