I have a form which is connected with force.com object, Is it possible to restrict a user to fill a form twice.
i.e Once user has submitted a survey, and if he trying to re submit a new survey it will not allow him and will display a message saying you have already submitted the survey.
What you can do is add a field ( or use an existing field ) on your Salesforce object to flag if the client has already responded.
Adding a boolean field 'hasCompleted' defaulted to 'false' would work, then when your FormAssembly form submits, it includes a mapping to make the field 'hasCompleted' be 'true'. If the object being updated already has an 'hasCompleted' that is true, this can trigger an error and prevent the response, depending on how you configure the Apex trigger. Salesforce Support can give you more details about setting up a trigger in your organization and customizing the error message on the Salesforce side. And of course the same logic would work for a field like 'responseStatus', etc.