Question

Has anyone tried to dynamically select which properties they want to write to an entity on appengine? For example:

I have a web form with 5 fields, and any given user will fill out some subset of those fields. I POST only the fields with data to the server (e.g. Fields 1,2,4). On the server side, how do I elegantly write only properties 1,2, and 4? The Model class has a function that returns a dictionary of property names (Model.properties()), but how would I use it to select property names?

In SQL, I would build an INSERT or UPDATE statement by matching the fields POSTed against the Model.properties() dictionary. I would look at the db module code in the Appengine SDK, to see if the Model class had some collection of Property objects, but I can’t find the module on my disk (I’m a little new to python and appengine).

Update: I read trunk/google/appengine/ext/db/init.py which confirmed that there is no way to refer to the properties as a group. Anyone know of a workaround?

Any thoughts?

Update2: This question was answered on the Google Group for AppEngine: http://groups.google.com/group/google-appengine/browse_thread/thread/b50be862f6d94b6e#

Answer 1

The python module will look something like this:

from google.appengine.ext.db import Key from google.appengine.api.datastore import Get, Put  def edit_item(request, db_id):      objKey = Key(str(db_id))      if request.method == 'POST':         objEntity = Get(objKey)         for k, v in request.POST.iteritems():              objEntity[k]=v         Put(objEntity)         return HttpResponseRedirect('/')      query = TestModel.get(objKey)     return render_to_response('edit.html', ({'modify_data': query,})) 

Your HTML should look something like this:

<form method='POST' action='.' enctype='multipart/form-data'>   Title: <input type='text' name='title' value='{{modify_data.field1}}'/>   Text: <input type='text' name='txt' value='{{modify_data.field2}}'/>    <input type='submit'/> </form>