Querying fields before merge
Sometimes it can be really nice (read: improve the user experience) to be able to query some fields without merging the value from the form back into an object. An example is when a user changes a input select field in a form which has an attached value. In an app we have, a user has a select list of product numbers. We make the app update the product's name on the page when the product changes.
Note that we are treading on thin ice here: if the user has not entered a valid value for the field, when get_value tries to convert it to the appropriate type, it will raise an exception that will need to be dealt with. It is (generally) safe to reference values from a TextField or a SelectField though.
The interesting part here is where we query the form for a specific field using its get_field method.
In the app itself, we use: