Create Action

In this lesson, we'll code a create action — 'C' in the 'CRUD' life cycle — that saves a new Post object and then redirects to the newly-created post's show page.

Before implementing this functionality, let's first open up a Rails console session and create a record manually:

post = Post.new
post.title = "Title Goes Here"
post.description = "Desc goes here..."
post.save

This syntax will let you manually create a new Post record with title and description attributes. After running the save method in the console, you will see output similar to the following:

 (0.1ms)  begin transaction
SQL (0.3ms)  INSERT INTO "posts" ("title", "description", "created_at", "updated_at") VALUES (?, ?, ?, ?)  [["title", "Title Goes Here"], ["description", "Desc goes here..."], ["created_at", "2015-11-23 22:26:43.799742"], ["updated_at", "2015-11-23 22:26:43.799742"]]
 (1.2ms)  commit transaction
=> true

As you can see, the save method generates a SQL script that inserts a new record into the database. Each of the Post object's attributes is passed into the SQL statement, and the method returns true upon a successful save. At a high level, this is what the create method in our PostsController will be doing.

Open up the posts_controller.rb file. Let's do a few things to replicate the behavior we had in the console:

Create a new Post instance
Pass in the parameters from the form
Save the record

To build this behavior initially, let's copy and paste the code that we ran in the console. The only key difference is that now, instead of assigning post.title and post.description manually, we want to be able to pull in form data - stuff that a user has typed in and submitted. As long as the form is properly connected to the controller and model, we can populate the title and description attributes based on the user input:

def create
  post = Post.new
  post.title = params[:title]
  post.description = params[:description]
  post.save
end

You can access each of input values in a form using the hash syntax to grab the elements from the params hash. When a user submits a form, it is the params hash that contains all the input data. As long as the form is routed to the create method we've written (in config/routes.rb), we'll be able to initialize a new instance of Post, grab those input values from params, assign them the post instance attributes and save the instance to our database.

We've already got the route and our form created. If you go to /posts/new, fill out the form, and submit it, you'll get the error shown below.

That's OK! Rails is simply complaining that it can't find a create view template since, by default, it's trying to render a template called create.html.erb (which doesn't exist). Remember, Rails tries to map each controller action directly to a template. However, with actions like create, we don't want a view template –– all we want is for the action to communicate with the database and then redirect to a different page.

If you open up the console, you'll see that the record was successfully created in the database even though we ran into an error page. Our form and create action are working properly. How do we know the record was successfully created? There are a couple of ways to check:

Type Post.last into the Rails console, and it will display the most recently created record. We can look at the record's created_at attribute to ensure the timestamp is current.
We can also simply scroll up through the Rails server logs. All SQL statements are printed out in the log, so it's just a matter of locating the correct INSERT statement (example below):

 (0.1ms)  begin transaction
SQL (0.7ms)  INSERT INTO "posts" ("title", "description", "created_at", "updated_at") VALUES (?, ?, ?, ?)  [["title", "My Post"], ["description", "My desc"], ["created_at", "2015-12-26 18:00:31.393419"], ["updated_at", "2015-12-26 18:00:31.393419"]]
 (2.2ms)  commit transaction

To fix the 'missing template' error, we simply need to redirect the user after they've filled out the form. Let's do two refactors:

Update the code with a redirect that leverages a route helper method
Refactor the post variable into an instance variable

The revised create method should look something like this:

def create
  @post = Post.new
  @post.title = params[:title]
  @post.description = params[:description]
  @post.save
  redirect_to post_path(@post)
end

In this refactored create action, we're following the convention of redirecting to the new resource's show page. It stands to reason that a user who submits a new post would then like to view the successfully-created post. With that being said, the page flow is not set in stone, and we could've redirected the create action to the index action just as easily.

All our tests should be passing now, and the site is working in the browser. Users are able to create records in the database using the HTML form, and, upon submitting a new post, they're automatically redirected to the show page for the post they just created. In future lessons, we'll refactor this further to incorporate awesome Rails components like strong parameters and error handling, but don't worry about those yet. Great job!

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florapetersen/rails-create-action-readme-onl01-seng-pt-052620

Create Action