This allows us to use the cookbook code that was downloaded with InstantRails, instead of a new copy of that code. Why is this important?

Size: px

Start display at page:

Download "This allows us to use the cookbook code that was downloaded with InstantRails, instead of a new copy of that code. Why is this important?"

Shon Nash
5 years ago
Views:

1 The Cookbook Application, cont. To bring up the Cookbook application, create a new Ruby project (rightclick in Package Explorer view, then New Project. We name the project cookbook and then deselect the Use default location checkbox. This allows us to use the cookbook code that was downloaded with InstantRails, instead of a new copy of that code. Why is this important? We find the downloaded code in C:\InstantRails\rails_apps\cookbook. Lecture 13 Object-Oriented Languages and Systems 1

choose Rails Applications > Open Ruby Console Window.

2 Click OK and then Finish. Then launch InstantRails. Click the little beige I box in the upper right-hand corner, and choose Rails Applications > Open Ruby Console Window. This gives you a terminal window: CSC/ECE 517 Lecture Notes 2007 Edward F. Gehringer 2

$Type cd cookbook, then ruby script\server.$ Then we can bring up a Web browser and browse to

3 Type cd cookbook, then ruby script\server. This starts the Web server. Then we can bring up a Web browser and browse to which redirects to Lecture 13 Object-Oriented Languages and Systems 3

Where shall we make this change? Well, if we click on Show all categories, we get this screen.

4 We can then proceed to exercise the application as we did in the last lecture. But now we can change its functionality too. Let s make a trivial change: Change Show all recipes and Show all categories to List all recipes and List all categories. Where shall we make this change? Well, if we click on Show all categories, we get this screen. What do you notice about the bottom line? And if we click on Create new recipe, we get this screen: CSC/ECE 517 Lecture Notes 2007 Edward F. Gehringer 4

5 Again, the bottom line is the same. Let s take a look at the directory listing. Which file do you think contains that code? Lecture 13 Object-Oriented Languages and Systems 5

6 This is an.rhtml file, the first time we ve seen this type. What do you think it stands for? Let s look at the code in this file. <html> <head> <title>online Cookbook</title> </head> <body> <h1>online Cookbook</h1> %> <p> <%= link_to "Create new recipe", :controller => "recipe", :action => "new" %> <%= link_to "Show all recipes", :controller => "recipe", :action => "list" %> CSC/ECE 517 Lecture Notes 2007 Edward F. Gehringer 6

7 <%= link_to "Show all categories", :controller => "category", :action => "list" %> </p> </body> </html> This raises several questions. What gets invoked when we click on the Show all recipes link? How do we make it say, List all recipes? What do? What s that strange notation Where is it specified that a standard layout is used for certain view screens? And if we poke around and look at all the views, we will find that all have the same navigation bar at the bottom. Now, to make sure you are following, here are some review questions. 1. What is the function of ruby script/server? Lecture 13 Object-Oriented Languages and Systems 7

8 2. What URL do we type in to find the homepage of our cookbook application? 3. When we click on Show all categories, what URL will be taken to? 4. What are the filenames that contain views associated with recipes? 5. What is Embedded Ruby, and how have we seen it used? 6. What kind of relationship is there between recipes and categories? 7. Where is this relationship represented? The views Now, let s take a look at the View code. We ll look at it line by line, which may obscure the flow, but if you have trouble, just look in your rails_apps/cookbook directory for the uncommented code. <form %>" method="post"> There are three main components here. The <form> tag The ERB code %> The POST method. <input id="recipe_id" name="recipe[id]" size="30" type="hidden" %>" /> You probably won t figure this out, so I ll tell you CSC/ECE 517 Lecture Notes 2007 Edward F. Gehringer 8

9 recipe_id is a field in the recipes table of the database. recipe[id] is a field of a hash called recipe that will be passed back as POST parameter. This is a hidden field because the ID (the primary key of the recipes table) has no reason to appear on the form that edits a recipe. However, it does need to be passed to the update method, so that method knows which row of the table to update. You should be able to figure out what the ERb means, but where is that instance variable set? <p><b>title</b><br> <input id="recipe_title" name="recipe[title]" size="30" type="text" %>" /> </p> Can you explain this, by analogy with the previous <input> tag? The next field is very similar <p><b>description</b><br> <input id="recipe_description" name="recipe[description]" size="30" type="text" %>" /> </p> <p><b>category:</b><br> Now we use a <select> form to put up a list (dropbox) of categories. <select name="recipe[category_id]"> do category %> <option value="<%= category.id %>" <%= ' selected' if category.id %>> Lecture 13 Object-Oriented Languages and Systems 9

10 <%= category.name %> </option> <% end %> </select></p> What does 'selected' do here? <p><b>instructions</b><br> <textarea cols="40" id="recipe_instructions" name="recipe[instructions]" rows="20" wrap="virtual"> %> </textarea> </p> <input type="submit" value="update" /> </form> The rest should be fairly self-explanatory. list.rhtml Now that we have seen one view, the next one is not very different. It begins with some garden-variety HTML <table border="1"> <tr> <td width="40%"><p align="center"><i><b>recipe</b></i></td> <td width="20%"><p align="center"><i><b>category</b></i></td> <td width="20%"><p align="center"><i><b>date</b></i></td> </tr> Then we cycle through each recipe, displaying it, if that is the appropriate thing to do. Where did instance variable come from? How is it deciding whether to display a recipe? CSC/ECE 517 Lecture Notes 2007 Edward F. Gehringer 10

11 do recipe %> <% if == nil) == recipe.category.name)%> <tr> Where does variable come from? Let s consider each of the parameters of the link_to calls below. The first link is to a scaffold method (which we can consider to be magic for now, but if you really want to see it, from a command window, execute ruby script/generate scaffold <model> <controller>, where <model> and <controller> are both recipe in this case). <td> <%= link_to recipe.title, :action => "show", :id => recipe.id %> The next link is to the delete method, which has a :confirm parameter. This is a feature of Rails, which pops up a dialog box for confirmation before deleting the recipe. <font size=-1> <%= link_to "(delete)", {:action => "delete", :id => recipe.id}, :confirm => "Really delete #{recipe.title}?" %> </font> </td> The next link displays recipe.category.name and passes two parameters. What is the :category parameter? Lecture 13 Object-Oriented Languages and Systems 11

12 <td> <%= link_to recipe.category.name, :action => "list", :category => "#{recipe.category.name}" %> </td> <td><%= recipe.date %></td> </tr> <% end %> <% end %> </table> new.rhtml The only remaining controller is new.rhtml. It doesn t illustrate much that we haven t seen before, so I ll ask you the questions (below). <form action="/recipe/create" method="post"> <p> <b>title</b><br/> <input id="recipe_title" name="recipe[title]" size="30" type="text" value=""/> </p> <p> <b>description</b><br/> <input id="recipe_description" name="recipe[description]" size="30" type="text" value=""/> </p> <p> <b>category:</b><br/> <select name="recipe[category_id]"> do category %> <option value="<%= category.id %>"> <%= category.name %> </option> <% end %> </select> </p> <p> CSC/ECE 517 Lecture Notes 2007 Edward F. Gehringer 12

13 <b>instructions</b><br/> <textarea cols="40" id="recipe_instructions" name="recipe[instructions]" rows="20" wrap="virtual"> </textarea> </p> <input type="submit" value="create"/> </form> 1. Which controller is invoked when the form is submitted? Where is the code for this controller? 2. Where, and in what form, is recipe[title] sent? 3. What is the function of the do category %> loop? 4. What link or button do we press to submit this form? Active Record Our Ruby on Rails programs deal with objects, but they are mapped into relational databases. There s a mismatch here how are the database tables translated into objects, and how are objects created in the program saved to the db? Ruby on Rails solution is Active Record. In Active Record, Database tables correspond to Rails classes. Database records (rows) correspond to Rails objects. Lecture 13 Object-Oriented Languages and Systems 13

14 We can perform operations on tables by invoking class methods, as is done in the = = Category.find_all There are also methods that operate on database records. These are invoked on objects. Can you find some in the code below? class RecipeController < ApplicationController layout "standard-layout" scaffold :recipe def = = Category.find_all end def = = Recipe.find_all end def = = Category.find_all end def = = Date.today redirect_to :action => 'list' else render_action 'new' end end def delete Recipe.find(@params['id']).destroy redirect_to :action => 'list' end end Notice also that the fields of an object correspond directly to the fields of a database record. This means that Ruby code can directly manipulate fields in database records (well, it can retrieve them via, manipulate them, and save them back via ). CSC/ECE 517 Lecture Notes 2007 Edward F. Gehringer 14

Lecture 9. Forms & APIs 1 / 38

Lecture 9. Forms & APIs 1 / 38 Lecture 9 Forms & APIs 1 / 38 Final Project Proposal Due November 12th 11:59PM Should include: A summary of your idea A diagram with the db tables you plan to use& the relationships between them You can