We have a question about Triggers on SmartTarget. One of our customers has a particular need. They need to use a trigger that uses the value of a field entered by the user in the condition. We do not know what it's called because it can be variable. Is there a possibility to implement this type of triggers?
You can create a trigger that has free text values, this means that it can accept any user input from a text field. This however raises the question: How do you want to use it to build Promotions? You could in theory create a filter to match the trigger value to a schema field value so only content with that value in a certain field is shown. It's hard to understand exactly what you want without more specific example of your requirements.
From your comment "We have developed a form generator, something akin to Tridion Webforms. We want to use the values in the fields of these forms to create promotions. And we can not know the field name to define the trigger" - it sounds like editors should be able to create triggers 'on the fly' by specifying that certain fields in forms they create with the CMS can also be used as triggers. Creating triggers can be done programatically via the SmartTarget CD API (see http://www.tridiondeveloper.com/create-fredhopper-trigger-types-programatically) so you could, in theory create a small service to generate them on the fly and hook that into the deployer or template code. I would be careful though - giving editors the ability to create triggers might mean that you end up with an unusable and confusing system after a few months, with hundreds of one-off triggers for throw-away forms.
Its difficult to know if it might suffice, but you could just have a single generic form field trigger, and use a convention for the values, where you prefix them with the field name (so if your editor creates a "country" field, and the visitor selects "es" when filling in the form, the trigger value could be "country|es"). Its not very editor friendly for creating the promotions, but would avoid creating a mess of too many triggers.