Last week we built pure ruby views without touching the database. This week we will pull together ruby generated views and database stored content using rails. We will then create new views and routes to add data to our database with web forms. Submission is the same as last week, and directions are below.
Good luck, have fun!!
Note directions that start with $ indicate they are on the command line, you should not copy the $.
Go to the directory where you like to store your rails code.
Fork this project and then clone it to your local machine.
You will need ruby 1.9 or higher for this example. You can check your version of Ruby by running:
$ ruby -v
Once on your local machine you will need to navigate to the project directory and run:
$ bundle install
This might take awhile, afterwards you will need to run:
$ rake db:create
$ rake db:migrate
This will create a Users table and a Products table. The MVCr (Model View Controller (r)outes) for users has already been created. If you run your rails server by executing:
$ rails server
You can then visit localhost:3000/users/new in your browser and create a new user.
There is a controller for products in app/controllers/products_controller.rb but it is empty. There is one view for products in app/views/products/index.html.erb and one route to this view in config.routes.rb. It looks like this:
match '/products' => 'products#index'
This means that if you visit localhost:3000/products in your browser you will see the contents of the index view in the products folder, the one located in app/views/products/index.html.erb. In this exercise we will see how to add content from our database to our views, how to add information retrieved from our users to our database, and finally have a properly formatted MVCr for Products.
If you didn't already, create a user by visiting localhost:3000/users/new filling out the form and hitting submit.
In a new terminal run the rails console:
$ rails console
Loading development environment (Rails 3.2.6)
>
From here we can use our rails code and populate our database and perform queries against our database. If you were able to successfully create a user you should be able to see them in the console.
(Note from now on out the character > denotes that we are running in the rails console. If code isn't working check that you're not still in terminal $ and vice versa. Try not to copy and paste code, the process of typing it in will help you build up a muscle memory for the code, like learning to write a new language.)
> User.count
=> 1
> User.first
=> #<User id: 1, name: "richard", job_title: "professor", created_at: "2012-03-23 03:04:05", updated_at: "2012-05-14 05:23:06" >
(Note: the # character indicates a comment, anything after it will be ignored unless it is used inside of a string to like "the value of 1 + 1 is: #{1+1}". I will add notes about what is going on in the console following the naked # character. This is also how rails shows model objects when they are inspected. using #<User ...> for the User model and #<Product ... > for the Product model, etc. )
Now that you've got a user in your database lets make sure we can find them again with SQL. Take the name entered above (in this case richard) and search the database for it:
> User.first.name
=> 'richard'
> User.where(:name => 'richard')
=> [#<User id: 1, name: "richard", ... >]
Great that found ALL of the users named 'richard', if you got an empty array try again, make sure to use the name you used. If we wanted to find only one richard, we could limit the query and pull out the first user like this:
> User.first.name
=> 'richard'
> User.where(:name => 'richard').first
=> #<User id: 1, name: "richard", ... >
Cool, now we can store that user to a variable to use later:
> User.first.name
=> 'richard'
> rich = User.where(:name => 'richard').first
> rich.name
=> "richard"
> rich.job_title
=> "professor"
If you look in the user model apps/models/user.rb you will see that users have_many :products, and in apps/models/product.rb that products :belong_to user. In this imaginary scenario pretend each user is a vendor at some kind of market and is using this application to keep inventory. If you take a look at the product table by running:
> Product
=> Product(id: integer, user_id: integer, name: string, price: integer, created_at: datetime, updated_at: datetime)
You will see that each product contains a foreign key called user_id lets add a product to our user. Using the existing variable from previously we can see all of our user's products:
> rich = User.where(:name => 'richard').first
> rich.products
=> []
There aren't any yet, so lets make one
> rich = User.where(:name => 'richard').first
> rich.products.create(:name => "rails book", :price => 19)
=> #<Product id: 1, user_id: 1, name: "rails book", price: 19, created_at: "2012-06-23 19:11:44", updated_at: "2012-06-23 19:11:44">
Awesome, now we should be able to query our database to find that product
> Product.where(:name => 'rails book').first
=> #<Product id: 1, user_id: 1, name: "rails book", price: 19, created_at: "2012-06-23 19:11:44", updated_at: "2012-06-23 19:11:44">
We can even drop to raw SQL in our where statement and look for all products greater than a given price:
> Product.where("price > 5")
=> [#<Product id: 1, user_id: 1, name: "rails book", price: 19, ... > ]
Once you have a product you can also get access to it's owner
> cheap_book = Product.where("price > 5").first
> cheap_book.user
=> #<User id: 1, name: "richard", ... >
This is possible because of our primary and foreign key relationship and because we told Rails how to use our database in the models/user.rb and models/product.rb files.
If any of this is new or confusing information please review Week 2, or simply try going over this example, and calling to_sql on queries to better understand relationships.
You should have at least one user and one product in your database at this point and time, if you don't please start over from the beginning. You will now run a script that will generate many fake users and many fake products, the technical term for this is "seeding" the database with fake data. We are using a gem called 'ffaker' but you don't need to know that. In the terminal (not the rails console) run this command:
$ rake fake:data
If you got no output at all, check you are in the rails directory by running ls
$ ls
Gemfile README.md app config.ru doc log script tmp
Gemfile.lock Rakefile config db lib public test vendor
Go back into your rails console and do a count on users and products, you should now have many more:
$ rails console
Loading development environment (Rails 3.2.6)
> User.count
=> 101 # your number might be different
> Product.count
=> 254 # your number might be different
Your numbers might be different but it should be more than 1.
Now that we have a bunch of users and associated products, lets do something useful with them. Previously we noted that localhost:3000/products was linked to the view app/views/products/index.html.erb through a route in our config/routes.rb file. Open the index.html.erb view now in a text editor (i recommend sublime text 2 for mac). Make sure your rails server is started ($ rails server) and visit localhost:3000/products in your browser.
Add this to the top of the index.html.erb file:
<h2>Hello World</h2>
When you refresh your page you should see the new text:
If you don't, go back and follow the prior steps.
If you look in your rails server log (this is the code that gets spewed from terminal after you run $ rails server), you should be able to see a line in there that looks like this
Started GET "/products" for 127.0.0.1 at 2012-06-23 14:29:31 -0500
(Note: we are using the quiet_assets gem, if you do this on another project your output will still have the same info, but it will also have a bunch of useless output for debugging as well.)
This is telling us that we are using a GET request on the /products url, and since our routes have that mapped to products#index in our routes.rb file, our server log will tell us that combination of HTTP action and URL that we are looking at is located in the products controller and index action:
Processing by ProductsController#index as HTML
Finally it will tell us that the view it rendered is coming from products/index.html.erb and that is is using the layouts/application file.
Rendered products/index.html.erb within layouts/application (0.2ms)
We also learn that the request was a 200 response which is how computers say everything was good. If it was not a good response we might see a 404 or 500 response. On redirects we can expect a 301 or 302 response.
Completed 200 OK in 7ms (Views: 6.7ms | ActiveRecord: 0.0ms)
All together the log looks like this:
Started GET "/products" for 127.0.0.1 at 2012-06-23 14:36:08 -0500
Processing by ProductsController#index as HTML
Rendered products/index.html.erb within layouts/application (0.2ms)
Completed 200 OK in 7ms (Views: 6.7ms | ActiveRecord: 0.0ms)
There is a lot of information in a tiny package. When things go wrong in your app, you can use the log output to verify your assumptions are correct and to get error messages.
Visit this url: localhost:3000/users and then find the log entry. Then open up the readme.md you copied onto your local machine and fill out this information:
HTTP verb used in this request: GET URL: /users Controller Name: UsersController Controller Action: index View File Name: index.html.erb Layout File Name: application.html.erb Response code of the request: 200
You should also notice a new line or two that we didn't see before, what is it (copy and paste, hint: after User Load) ? User Load (3.2ms) SELECT "users".* FROM "users" Why do you think this line is there? get user data from the database.
Save and commit your answers.
We've started our rails app, we've loaded data into our Models, we've connected our Routes to our Controller and View, and we've modified our view index.html.erb we also learned a thing or two about digging for info in the logs. Now we're going to pull products out of the database and put them into our products view.
As we saw in last week's exercise we can use ruby code in our views by adding ERB tags <%= "I am an ERB tag" %>. Open up the file app/views/products/index.html.erb` We will now add some model code directly to our view.
At the very top of the view add this:
<% first_product = Product.first %>
Refresh the localhost:3000/products page, you shouldn't see any changes since we excluded the = from our erb block, but check the log... notice anything different? You should see this line:
Product Load (0.1ms) SELECT "products".* FROM "products" LIMIT 1
We just put a SQL query into our view!!! Now lets use it:
<% first_product = Product.first %>
<p>
Product Name: "<%= first_product.name %>"" costs $<%= first_product.price %>
</p>
Refresh the web page and you should see something like this in your view:
Product Name: "rails book" costs $19
Check your log again and see what the SQL query is now. Is it the same?
Since we have a relationship between our products and our user we can show the owner of this product in the view. Add this line to your view (after the first_product variable assignment).
<p>
The seller for this product is named '<%= first_product.user.name %>'
</p
Check your logs again, did the SQL change? Are there any new statements, why?
We've pulled data out of our database and into our rails view, pretty sweet. But the product from Product.first isn't very interesting. Make a new ERB tag and in it make a different type of query, storing the value to a variable. <%= product = Product.where(:name => 'rails book').first %> or <%= cheap_product = Product.where('price > 1').first %>.
Then output the name of the product, it's price and the name of the owner of the product. After each take a look a the log and see if there are new SQL statements listed.
In addition to searching for whole products we can add meta data such as Product count to the page. Add an erb block to the page that shows how many products are in the database.
By now you should have several ERB blocks that have a variable assignment in them, they will have a variable such as first_product on the left and right next to them will have a single equals = this is an example of a variable assignment:
<% first_product = Product.first %>
Try moving one or more to different places in the view file, what happens? What if you move one of them to the bottom? What if you move ALL of them to the top? Does one break? Does one look/feel better?
Commit the results to git.
Hopefully you feel comfortable writing sql using Rails and Active Record and inserting it into your views. So far we've been working with individual objects by calling .first on our queries. Lets add a whole bunch of data to this view by listing the name and price of every single item in our database!!! How do we do that? We will be using Product.all which will pull all of the products from our database for us. The result of this query in Ruby will be an array of product objects. Since we now have an array, we can use Array#each like we did in last weeks assignment to turn all those products into a list.
Delete all the contents of app/views/products.index.html.erb don't worry we've got a backup in GIT if you need it. We want to start with a fresh slate. Add this code to index.html.erb
<% lots_of_products = Product.all %>
Now that we have all of our products, refresh the page and you should see this line in your log
Product Load (0.8ms) SELECT "products".* FROM "products"
We are getting all of the products in our database and loading into memory. This whole process took 0.8ms which is pretty quick but much much longer than some of our other queries such as:
User Load (0.1ms) SELECT "users".* FROM "users" WHERE "users"."id" = 1 LIMIT 1
Loading a single user which only take 0.1ms. Comparing the two loading all the products is 8 times slower.
We'll be worried about performance later, for now lets use all that massive amounts of data. Add this code to your view:
<ul>
<% lots_of_products.each do |product| %>
<li>
<%= product.name %>
</li>
<% end %>
</ul>
Refresh the page and whoa, you should see a ton of products listed!! If you didn't go check your logs and try to figure out why.
This is a good start but lets give more information. Change that code to match the code below:
<ul>
<% lots_of_products.each do |product| %>
<li>
Product Name: "<%= product.name %>"" costs $<%= product.price %>
</li>
<% end %>
</ul>
Now refresh the page, pretty cool huh. Lets also add the data about who is selling it by using our ActiveRecord association <%= product.user.name %>:
<ul>
<% lots_of_products.each do |product| %>
<li>
Product Name: "<%= product.name %>"" costs $<%= product.price %>
Sold by <%= product.user.name %>
</li>
<% end %>
</ul>
Refresh the page and see your new data. Now check the log and, what happened? Your log is now spammed by a ton of sql statements
User Load (0.2ms) SELECT "users".* FROM "users" WHERE "users"."id" = 78 LIMIT 1
CACHE (0.0ms) SELECT "users".* FROM "users" WHERE "users"."id" = 78 LIMIT 1 CACHE (0.0ms) SELECT "users".* FROM "users" WHERE "users"."id" = 78 LIMIT 1 CACHE (0.0ms) SELECT "users".* FROM "users" WHERE "users"."id" = 78 LIMIT 1 CACHE (0.0ms) SELECT "users".* FROM "users" WHERE "users"."id" = 78 LIMIT 1 User Load (0.2ms) SELECT "users".* FROM "users" WHERE "users"."id" = 79 LIMIT 1 CACHE (0.0ms) SELECT "users".* FROM "users" WHERE "users"."id" = 79 LIMIT 1 CACHE (0.0ms) SELECT "users".* FROM "users" WHERE "users"."id" = 79 LIMIT 1 User Load (0.2ms) SELECT "users".* FROM "users" WHERE "users"."id" = 80 LIMIT 1 CACHE (0.0ms) SELECT "users".* FROM "users" WHERE "users"."id" = 80 LIMIT 1 CACHE (0.0ms) SELECT "users".* FROM "users" WHERE "users"."id" = 80 LIMIT 1 CACHE (0.0ms) SELECT "users".* FROM "users" WHERE "users"."id" = 80 LIMIT 1 User Load (0.1ms) SELECT "users".* FROM "users" WHERE "users"."id" = 81 LIMIT 1 CACHE (0.0ms) SELECT "users".* FROM "users" WHERE "users"."id" = 81 LIMIT 1 CACHE (0.0ms) SELECT "users".* FROM "users" WHERE "users"."id" = 81 LIMIT 1 User Load (0.1ms) SELECT "users".* FROM "users" WHERE "users"."id" = 82 LIMIT 1 CACHE (0.0ms) SELECT "users".* FROM "users" WHERE "users"."id" = 82 LIMIT 1
How did this show up? If you go to the top of the log entry you'll see where we loaded all products using <% lots_of_products = Product.all %> which translated to SQL of Product Load (1.4ms) SELECT "products".* FROM "products" the problem comes with this innocent looking line Sold by <%= product.user.name %>. We did a good job of pulling all the products out in one query, but then we iterated over each and every one of them and pulled out the user. This means for every product in our database (n) we performed one extra query (n + 1). This is known as the n + 1 problem. Note how long that view took to load, for me it was around 252(ms)
Completed 200 OK in 252ms (Views: 238.1ms | ActiveRecord: 13.5ms)
We can use a construct in ActiveRecord called includes that eagerly loads all of the user associations when we are doing our initial query. So you can replace this line:
<% lots_of_products = Product.all %>
With this line:
<% lots_of_products = Product.includes(:user).all %>
Reload the page and wow, my load time dropped by half
Completed 200 OK in 102ms (Views: 99.3ms | ActiveRecord: 2.1ms)
You can also see that our database was a little smarter, instead of n+1 queries we only have two, for me they look like this:
Product Load (0.9ms) SELECT "products".* FROM "products"
User Load (0.7ms) SELECT "users".* FROM "users" WHERE "users"."id" IN (1, 2, 4, 5, 6, 7, 8, 9, 10,
12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 31, 32, 33, 34, 35, 37, 38, 39,
40, 41, 42, 45, 50, 51, 52, 53, 54, 55, 56, 60, 62, 63, 65, 66, 68, 70, 71, 72, 73, 74, 75, 76, 77,
78, 79, 80, 81, 82, 83, 84, 86, 87, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 100, 101)
You don't always want to use includes() when using active record, but it is one tool in your toolbox for getting a faster page load, just check the logs for the tell tell sign of an n+1 problem if you see a ton of SQL queries getting spammed on each and every page refresh. Using includes() when you don't have this problem will actually slow down your page.
Commit your results to git
If you wanted to speed up the page more how could you? Take a look at an amazon search. Do they show you all the products on one page? At the bottom of the page, you can go to next and previous pages, this is called pagination.
SQL has the operators LIMIT which restrict the number of results you get, as well as OFFSET which will essentially skip the number of entries you specify in the result. For example if you were returning 100 elements and you had an offset of 10, you would return elements 11 through 100.
Do you think it would be possible to add pagination to this page with just LIMIT and OFFSET?
No code or submission is required, just think about it.
We saw that we have a few pages in our app that relate to users, as well as this one that we made that relates to products. We should add a link to our users list page (UsersController#index) as well as our products list page (ProductsController#index) in our layout.
Open the layout file app/views/layouts/application.html.erb. Like last week's exercises this contains a layout that will be rendered for all pages on our site. Last week we made our own view helper called link_to where we could pass it in a name for the link and a url and it would give us a link. Rails already has a link helper so add a link to your application.html.erb file, put it after the first <body> tag.
<%= link_to "Schneems Blog", "http://schneems.com" %>
Refresh your web page, you should now see a link on your page. Click it to make sure it works. This is an absolute link since we included the protocol (http://) and domain (schneems.com). If you want to link to the user list page you can add a relative link, that just starts with a '/'
<%= link_to "User List", "/users" %>
You can then add one for products
<%= link_to "Product List", "/products" %>
By default all links use GET requests. Now users of your website can navigate around a bit easier and not have to type in urls.
If you want to see how rails knows what to do when you go to /products in your browser, open up a new terminal window and navigate to this rails directory. Then run
$ rake routes
You should see an output like this:
products GET /products(.:format) products#index
users GET /users(.:format) users#index
POST /users(.:format) users#create
new_user GET /users/new(.:format) users#new
edit_user GET /users/:id/edit(.:format) users#edit
user GET /users/:id(.:format) users#show
PUT /users/:id(.:format) users#update
DELETE /users/:id(.:format) users#destroy
The output is a bit cryptic, but lets dig into the first line in my output.
products GET /products(.:format) products#index
The first element products refers to a url helper that we can use in our views. Rather than having to type '/products' directly into our view we could use products_path that might seem silly now, but we won't see the benefit from this till later.
The next element GET refers to the HTTP verb that the url is accessible at.
The next /products(.:format) means that this route lives at the path /products. So in your browser at your domain http://localhost:3000 if you visit /products it applies to this route. Note we could have multiple /products urls but we can use the HTTP verb to differentiate them (use POST or DELETE instead). The contents of (.:format) refer to an optional section. The period . is literal, the :format means that anything you type there will be turned into a format parameter. Confused? We'll get back to this in one second [1]
The last element products#index tells us what controller and action we are calling. By default controllers will render the view with the same name, so products controller index action will render app/views/products/index.html.erb.
[1] If you were confused by that optional format thing, you weren't alone. Rails routes can be very sophisticated and while we've been going to naked path's you could add on the format /products.html and it would work just fine. Go ahead and try http://localhost:3000/users.html. If you check your logs you'll even see that your server knows it is an HTML request.
Processing by UsersController#index as HTML
In addition to html we could add json, or xml, but that's getting ahead of ourselves. Above i mentioned that we could get the format parameter from the url, how do we do that? Add this to your app/views/layouts/application.html.erb after the tag and before the <%= yield %> tag:
<%= params[:format] %>
You should now see html in your view when your refresh your page. Lets see what other types of goodies params has. Add this to your layout:
<%= params.inspect %>
Now refresh the page and you should see something like this:
{"action"=>"index", "controller"=>"users", "format"=>"html"}
Rails automatically adds useful things to our params variable for views. We can get data out of our query string using params. Keep that line in your layout and visit this url http://localhost:3000/users?instructor=schneems&quality=awesome
Rails will pull the data out of your query string and add it to params you should see this in your page:
{"instructor"=>"schneems", "quality"=>"awesome", "action"=>"index", "controller"=>"users"}
We'll use this quite a bit later on, but for now it's just a fun demo.
Homework:
Remove all the references to params from your layout, change your link_to erb tags to use the propper rails helpers. I.E. replace this:
<%= link_to "User List", "/users" %>
With this
<%= link_to "User List", users_path %>
Do the same for the products link, click on them to make sure they work. If you get stuck try running $ rake routes in the terminal or re-reading this section.
save and commit the results to git
We've got the start of a pretty good application that shows us all the products in our database. So far in our CRUD operations for our products resource, we've implemented one, Read. In this exercise we will be adding the ability to create new products using a web interface like we can with users. Excited? You should be.
What do you do when you want to create something? If you want to make a drawing, you get a new sheet of paper. If you want to create a table you get some new lumber. Likewise we'll start off creating a new view. Create a file named new.html.erb in the products view folder, the full path should be app/views/products/new.html.erb this is where we will put the form for our products. Now add some simple text to the file:
<h2>New Products View</h2>
Now go to http://localhost:3000/products/new. And whoa, what happened? Where is our view? What is this routing error thing? Although we've got a view file and a products controller, the error is telling us that:
No route matches [GET] "/products/new"
If you run $ rake routes in another terminal, you'll see that your rails app is right (it usually is) that there is no line that has the path /products/new in it so lets make one. Open up your routes config/routes.rb and add this line:
get '/products/new' => 'products#new'
Here we are telling our app that the path /products/new should map to our products controller, the new action. Refresh the page and it should render (make sure routes.rb is saved first). If it doesn't look in your log and try tracing your steps backwards, did you forget a step?
Now that we've got our Model in place, our Controller, and our Routes for this view file (M_Cr) we need to finish our view before our (MVCr) for this action is complete. Open up app/views/products/new.html.erb here we will add a form where a visitor to our website can add a product.
In the last homework we added a simple form, we will do the same thing here, when a user submits the form the will be adding data to our database, we want the form to use a POST action. We will want to include the name of our product as well as a price. First we will start off by adding the form tags
<form method='post' action='/products' >
</form>
This tells the browser that when we submit this form it will submit to the /products path using a method of post. Remember we can re-use the /products path that we used for index, since this is a POST action and index uses a GET. (Routes = URL + HTTP Method). Next we want to add a text field:
<form method='post' action='/products' >
<input name="product[name]" size="30" type="text">
</form>
Here the type of the input field is "text" and it will be 30 characters wide. When we submit this form we can find the result of this field in the product[name], Rails will translate this to params[:product][:name] for us for ease of use. Refresh the page.
Add a label above the text field
<form method='post' action='/products' >
<label>Name</label><br>
<input name="product[name]" size="30" type="text">
</form>
Great now add a submit button:
<form method='post' action='/products' >
<label>Name</label><br>
<input name="product[name]" size="30" type="text">
<input type="submit" value="Create Product">
</form>
Here we are adding an input element with type='submit' which indicates it will be the submit button. We can control the text in the button by change the text inside of it's value. For now it isn't important to memorize the syntax of this html just be able to read it and modify it.
Lets add our price and then test out the form:
<form method='post' action='/products' >
<label>Name</label><br>
<input name="product[name]" size="30" type="text">
<br />
<label>Price</label><br>
<input name="product[price]" type="number">
<br />
<input type="submit" value="Create Product">
</form>
Again we are storing the price inside of the product hash (in rails terms) so we can get to it by using params[:product][:price] later. Instead of a text type we are designating this as a number field.
We've got everything we need to build a product (minus a user which is out of scope for this example). Fill out the form and hit "Create Product" and...
We get another routing error. We only implemented the view for the form, but didn't write any of the logic for persisting (storing) the data to the database. Lets do that now.
Open up config/routes.rb and add this line:
post '/products' => 'products#create'
You will then need to make a new view create.html.erb in the folder app/views/products/ (hopefully, you're noticing a trend), the full path will be app/views/products/create.html.erb. Open this file and add this to it:
<h2>Create View</h2>
<%= params.inspect %>
Refresh the page, you will be prompted if you are sure. This is a safety feature due to the browser recognizing the POST action. Most POST actions such as ordering an item off of amazon or ebay are intended to happen only once. Refreshing the request could lead to unwanted duplicate orders. For now we haven't written the logic to persist to the database, so click okay.
If you accidentally close this page just go back to /products/new and re-submit the form.
You should see something like this:
Create View
{"product"=>{"name"=>"bird house", "price"=>"999"}, "controller"=>"products", "action"=>"create"}
So here we have all the data we need to create our product. Remember in the console we can run:
> Product.create(:name => "bird house", :price => 999)
To create a product. Since params is a hash we can change our view to this
<h2>Create View</h2>
<%= params[:product].inspect %>
Now refresh the page, you should see something like this:
{"name"=>"bird house", "price"=>"999"}
This looks dangerously close to what we needed to pass to Product.create in order to actually save our info to the database. Lets try it out. In the bottom of your view add this line:
<%= Product.create(params[:product]).inspect %>
Refresh the page, now you should see something like this
#<Product id: 225, user_id: nil, name: "bird house", price: 999, created_at: "2012-06-23 22:15:09", updated_at: "2012-06-23 22:15:09">
If our product has an id, that means it saved. We now have that product in our database. To prove it you can open a $ rails console and run this (replacing your id):
> Product.where(:id => 225).first
> #<Product id: 225, user_id: nil, ... >
Thats pretty cool, we just built a way to insert data into our database from a website, it might not be pretty but it works!!
Refresh the page again, and the product id should be incremented:
#<Product id: 226, user_id: nil, name: "bird house", price: 999, created_at: "2012-06-23 22:16:48", updated_at: "2012-06-23 22:16:48">
But that doesn't seem right now we have two products with duplicate names. Lets tell Rails that shouldn't happen. We'll tell rails to validate the uniqueness of the name field on products. Open your product model
app/models/product.rb and add this code in:
validates :name, :uniqueness => true
Now refresh the page and the product id is gone! The duplicate product wasn't saved.
<Product id: nil, user_id: nil, name: "bird house", price: 999, created_at: nil, updated_at: nil>
To understand why it isn't saving lets change our view code a bit, first replace this line:
<%= Product.create(params[:product]).inspect %>
With this:
<% product = Product.create(params[:product]) %>
<%= product.inspect %>
Refresh the page, and you should see the exact same thing. Now add this to the bottom of your view
<br />
<%= product.errors.inspect %>
You should see an output that looks similar to this:
#<ActiveModel::Errors:0x007fdc62bb1b38 @base=#<Product id: nil, user_id: nil, name: "bird house",
price: 999, created_at: nil, updated_at: nil>,
@messages={:name=>["has already been taken"]}>
Since we told rails that all valid products have a unique name, and rails will only save valid products, this error prevented the product from getting saved. The message tells us why :name=>["has already been taken"], the name has already been taken.
Since this is a common occurrence we will need to check for this type of a thing in our code.
Rather than use the create command in our code we can make a new object and then run save on it (create does both at the same time). Lets remove this line:
<% product = Product.create(params[:product]) %>
and replace it with this
<% product = Product.new(params[:product]) %>
<%= product.save %>
Which essentially does the same thing, but the out put of product.save is a boolean (true or false) we can use this to show different message to our user if it saves or not.
Add this to your view:
<% if product.save %>
<h2> Congrats You Created a New Product</h2>
Your product looks like <%= product.inspect %>
<% else %>
<h2>Your product was not saved!! </h2>
<%= product.errors.full_messages %>
Please go back in your browser and fix the problem
<% end %>
Refresh the page again you should see
Your product was not saved!!
["Name has already been taken"]
Please go back in your browser and fix the problem
Thats much more useful to our user.
Homework:
Commit results to git & smile
Congrats, you're done, you've come pretty far since last week. Last week you were barely scratching the surface of generating html with ruby, and now you've completely written half of a CRUD server (for products). Think about that, you took data from a database and brought it to life in the browser. You then turned around and figured out a way to send data from a web form back to your database. That's pretty amazing. We also didn't use much Rails magic, for our models we used vanilla ActiveRecord Ruby objects, for our views we used (mostly) vanilla Ruby ERB. We did use this special Routes thing, and this special controller thing, but not very much.
Now that you understand the basics of sending and retrieving data from a database, next week we can start to use some more rails practices to clean up your code and make life a little easier for yourself. If you were curious and decided to poke around in the views and controller for User, you might be a little surprised by how different it is, don't worry most of that is organization and is quite a bit harder to understand without the fundamentals we've just experienced.
The most important thing to take away from this MVCr exercise is that you can (and should) build everything incrementally. It's okay to not understand the bigger picture until after you're done. Taking many small steps and checking yourself after each is the best way to stay on course, no matter what the activity is.