Change db.ComputedProperty from StringProperty to TextProperty
Have your computed property return an instance of db.Text instead of a String. As Wooble points out, though, there's absolutely no point in doing this: the computed property exists to aid indexing, and if you're not indexing the data, you may as well use a regular property and not store it in the datastore at all.
I am kind of new to GAE and I was trying to use @db.ComputedProperty to dynamically add field values
However I am getting the error message
Property xxxx is 721 bytes long; it must be 500 or less. Consider Text instead, which can store strings of any length.
It seems that @db.ComputedProperty defaults to StringProperty
Is there any way to change it to TextProperty?