Thing you should know before moving your Django app into Google App Engine

Django's model has "id" field. It is auto-increment, unique integer for each models. GAE Datastore also has "id" field. It is *not* auto-increment, unique integer for *all* models. And you can not set the field as you want. This is annoying.

If you use Django's "id" field in permalink etc. (as I did), you need to add some field like "oldid", move old "id" value in it and write some code to put such a value in new coming items. For your information, when you can't inherit User models, you need to make a wrapper model. And also, you should change all code searching items with "id". You should change all "get_absolute_url" methods to use "oldid" in place of "id".

That is not all problem you should overcome. GAE Datastore doesn't allow inequality filter on more than one fields. If you use it, you should change the logic. Some of them are solvable with result caching. If you use SQL directly for speed-up, it won't work. Some query take more time or doesn't return correct value and there is DeadlineExceededException. You need tune-up in GAE way. You can't know how much items in your Datastore if it is more than 1000, in such case count() always return 1000.

Three month before, I thought it is easy task. Now I am convinced that I should rewrite the app. I hope it helps some people like me.