generate CommentType class for the Comment entity by running in console 'php app/console generate:doctrine:form AcmeBlogBundle:Comment'
we need to create a form on the blog show and process it so we must create a controller for Comment; after creating a comment we want to redirect to blog show page displayed around the location of the added comment
the constraint ensure both the user and comment members must not be blank and comment will be at least 2 characters long
create the template for render the comment form and the create view and update the blog show template to render the add blog form
update the create action of the Comment controller to persist the Comment entity to the database