Build me a simple rails app

What am talking about here is something like Quora. Just like when we add a question in Quora we have an option to ask the question anonymously. In this scenario, you have to create a rails app with devise for authentication ( A user will have the following fields NAME, SEX, EMAIL, PASSWORD ) then there will we another model POST (TITTLE, CONTENT). Now what i want is a feature called CODENAME, whenever a user creates a post he get an option to publish the post either with his name or he can create a codename exclusively for this post, the logic behind CODENAME will be that a user can have multiple CODENAME and a CODENAME can have multiple posts, also two users cannot have the same CODENAME. i don't want any type of css work or any kind design out there. Just simply this feature.