Understanding Scaffolding in Rails Better

Question

I've read the rails guides but there are some things that when I actually do it myself I still do not understand.

For example, how come when I visit my show view on localhost I get an error? Scaffolding created a show action in my controller that is empty and a view but still get an error message.

Similar thing happens with index.

Isn't the purpose of scaffolding to help you with all this? I assumed if I made a few posts that the index action would take me to an index of all the posts but it doesn't instead the post/ itself lists them all. What is the logic behind scaffolding doing this?

EDIT::::

This is the error message that I get:

ActiveRecord::RecordNotFound in ExperimentsController#show
Couldn't find Experiment with id=index

This happens when I visit http://localhost:3000/experiments/index

Answer 1

You are accessing the routes incorrectly. To visit the index page : you need url http://localhost:3000/experiments

When you specify url : http://localhost:3000/experiments/index, Rails would match it to the route of show page(as shown below): /experiments/:id

If you read the error carefully:

ActiveRecord::RecordNotFound in ExperimentsController#show Couldn't find Experiment with id=index

Rails mapped the url to show action and is trying to find an experiment with id=index which obviously does not exist and you get an error.

Run rake routes on command prompt and you'll see the routes created for resource experiment as follows:

           /experiments             index      display a list of all experiments
GET        /experiments/new         new        return an HTML form for creating a new experiment
POST       /experiments             create     create a new experiment
GET        /experiments/:id         show       display a specific experiment
GET        /experiments/:id/edit    edit       returns an HTML form for editing an experiments
PATCH/PUT  /experiments/:id         update     update a specific experiment
DELETE     /experiments/:id         destroy    delete a specific experiment

You can access the specific routes with the paths shown above. Replace :id with an existing experiment records id attribute value.

For eg:

To view an experiment with id 5 Visit http://localhost:3000/experiments/5

NOTE: I would highly recommend you to go through the Rails Routing Guide and get a better idea of how Routing works.

Answer 2

For a simple scaffolding task and assuming you followed the convention of naming, you should never get any errors, but even if you got an error my guess it will be a simple typo or pending-migrations type of error (something a quick googling should resolve)

Scaffolds are meant to give a push and increase Rapid Prototyping of your app but won't do the hole job for you.

I remember being confused just like you some time ago and i too was looking at the wrong direction trying to figure out what Scaffolding do while i should have looked on How Rails template system works which is the next step after learning Rails MVC basics.

Start from the guides, http://guides.rubyonrails.org/layouts_and_rendering.html#overview-how-the-pieces-fit-together and it will take some time to fully understand how rails works!