book

Head First Rails

Name: Head First Rails
Author: David Griffiths
ISBN: 9780596515775

by David Griffiths

December 2008

Intermediate to advanced

462 pages

9h 22m

English

O'Reilly Media, Inc.

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Dedication
A Note Regarding Supplemental Files
Advance Praise for Head First Rails
Praise for Head First Ajax
Praise for other Head First books
Author of Head First Rails
How to use this Book: Intro
Who is this book for?Who should probably back away from this book?We know what you’re thinkingWe know what your brain is thinkingMetacognition: thinking about thinkingHere’s what WE did:Here’s what YOU can do to bend your brain into submissionRead MeThe technical review teamAcknowledgmentsSafari® Books Online
1. Getting Started: Really Rapid Rails
Friday, 9 AMThe application needs to do lots of thingsSo what things do we need for the app?So how does Rails help us?Rails is for database-centric apps like the ticket sales systemYou create a new application with the rails commandSo what does this do?Now you need to add your own code to the default appRails apps always follow conventionsScaffolding is GENERATED codeSo what does the scaffold command do?There are no tables in the database yet!Create the table by running a migrationSweet! You saved your buddy’s job!So how can we change the labels?To modify an app, you need to dig into the app’s architectureThe 3 parts of your app: model, view, and controllerThe 3 types of code are kept in SEPARATE foldersThe files in the VIEW need to be editedEdit the HTML in the viewSunday, 8 AMThe application needs to store more information nowA migration is just a Ruby scriptRails can generate migrationsGive your migration a “smart” name, and Rails writes your code for youYou need to run your migration with rakeTimestamps tell rake which migrations to run, and in which orderBut changing the database isn’t enoughThe concert is a sell-out!Tools for your Rails Toolbox
2. Beyond Scaffolding: Rails apps, made to order
MeBay, Inc. needs your helpMeBay will store their ads in a databaseScaffolding does WAY too muchLet’s start by generating the MeBay model......and then we’ll actually create the table using rakeBut what about the controller?We’ve created the model and controller, now let’s move onto the view...The view is created with a page templateThe page template contains HTMLA route tells Rails where your web page isBehind the scenes with routesThe view doesn’t have the data to display appSo what should the page show?We need to display the data in the right placeThe controller sends the ad to the viewRails turned the record into an objectThe data’s in memory, and the web page can see itThere’s a problem — people can’t find the pages they wantRoutes run in priority orderTo get data into the view, you will also need code in the controllerAn index page will need data from ALL of the recordsSo how do you read more than one record?Ad.find(:all) reads the whole table at onceThe data is returned as an object called an arrayAn array is a numbered sequence of objectsRead all of the ads with a for loopWe need HTML for each element in the arrayRails converts page templates into Ruby codeLoops can be added to page templates using scriptletsOn each pass of the loop, the page generates one linkSo what does the generated HTML look like?You just got an email from the folks at MeBay...But there are two page templates... should we change the code of each one?A layout defines a STANDARD look for a whole set of page templatesYou need to REMOVE the boilerplate from your page templatesBut what about the new static content MeBay sent over?Tools for your Rails Toolbox
3. Inserting, Updating, and Deleting: Everything changes
People want to post new ads onlineYou already know how to build an app that publishes data from the databaseSaving data works just the OPPOSITE of reading dataYou need a form to submit data and an action method to save itAre forms and objects related?Rails can create forms that are associated with model objectsThe @ad form object has not been createdThe form object needs to be created before the form is displayedCan you think what the problem is with that?The forms ad object will be created in the new action of the controllerEach page template now has a matching controller methodThe form doesn’t send an object back, it sends DATA backBut how is the data FORMATTED?Rails needs to convert the data into an object before it can be savedThe model can create objects from raw form dataThe controller create method, step-by-stepThe controller needs to save the recordRails was complaining because it had no way of generating a RESPONSE to your requestDon’t create a new page, use an existing oneBut how can a controller action display ANOTHER action’s page?Redirects let the controller specify which view is displayedBut what if an ad needs to be amended after it’s been posted?Updating an ad is just like creating one... only differentInstead of creating an ad, you need to find one; instead of saving it, you need to update the adRestricting access to a function...but now old ads need to be deletedDoing it yourself gave you the power to do more than scaffoldingTools for your Rails Toolbox

4. Database Finders: Truth or consequences?
Keep fit with the Rubyville Health ClubThe scaffolding isn’t right—but do we write our own code or fix the scaffolding?The application actually looks pretty close...We’re going to fix the scaffoldingDesign the search functionSo here’s what you need to buildLet’s start by building the formThe search will need a new kind of formAdd the search to the interfaceSo are the form parameters structured differently?How do we find client records?We only need those records where client-name = the search stringThere’s a finder for every attributeSo what’s next?We need to match either the client name OR the trainer nameCan you see a problem here?We need to be able to modify the conditions used in the SQL queryUse :conditions to supply SQLThen there’s a knock at the door...Tools for your Rails Toolbox
5. Validating your Data: Preventing mistakes
Watch out—there’s bad data in the roomValidation code goes in the MODELRails uses validators for simple validationSo how do validators work?Let’s check if something is a numberUsers have been leaving out data on their workout formsSo can validators help?How do we check for mandatory fields?Validators are simple and work wellSomething strange has happened at MeBayThe validators work, but they don’t display errorsIf you build your own pages, you need to write your own error message codeThe controller needs to know if there was an errorWe still need to display error messages!The MeBay system is looking pretty sweetTools for your Rails Toolbox
6. Making Connections: Bringing it all together
Coconut Airways need a booking systemWe need to see flights and seat bookings togetherLet’s look at what the seat scaffolding gives usWe need the booking form and seat list on the flight pageHow can we split a page’s content up into separate files?ERb will ASSEMBLE our pagesSo how do we create the booking form partial?Now we need to include the partial in the templateWe need to give the partial a seat!You can pass local variables to a partialWe also need a partial for the seat listBut the seat-list partial needs an array of seatsPeople are ending up on the wrong flightsA relationship connects models togetherBut how do we define the relationship?But some people have too much baggageWe need to write our OWN validationWe need the REVERSE relationshipSo what does the Seat model look like now?The system’s taken off at Coconut AirwaysTools for your Rails Toolbox
7. Ajax: Avoiding the traffic
There’s a new offer at Coconut AirwaysWhich parts of a page change most?We need a way to update just the seat listDoesn’t the browser always update the entire page?So what ELSE can make a request?First we need to include the Ajax libraries......then we need to add an Ajax “Refresh” linkThe browser needs to ask for an updateBut SHOULD we make the browser ask over and over again?You listen to a timer like you listen to a buttonSomeone’s having trouble with their bachelor partyThe form needs to make an Ajax requestThe form needs to be under the CONTROL of JavaScriptWe need to replace the create methodSo what effect does this code have?There’s a problem with the flight bookingsWe only know how to update one part of the page at a timeSo what’s different this time?The controller needs to return JavaScript instead of HTMLSo what does Rails generate?If you don’t say where to put the response, it will be executedThe completed code can will now do several thingsTools for your Rails Toolbox
8. XML and Multiple Representations: It all looks different now...
Climbing all over the worldSo why isn’t it popular?The users hate the interface!The data needs to be on a mapWe need to create a new actionThe new action seems to work...The new page needs a map... that’s the point!So what code do we need?The code will only work for localhostNow we need the map dataWhat do we need to generate?We’ll generate XML from the modelA model object can generate XMLWhat will the controller code look likeMeanwhile, at 20,000 feet...Before your latest changesAfter your latest changesWe need to generate XML and HTMLXML and HTML are just representationsHow should we decide which format to use?How does the map page work?The code is ready to go liveRSS feeds are just XMLWe’ll create an action called newsWe have to change the structure of the XMLWe need more XML POWERSo we’ll use a new kind of template: an XML builderNow let’s add the feed to the pagesOn top of the world!Tools for your Rails Toolbox
9. REST and Ajax: Taking things further
Too many incidents!The map could show more detailsWe can extend the map using AjaxBut how do we convert the index page?What will the “show” action need to generate?The new map functionality is a success!We need to create requests using Ajax, tooSo what needs to change?The map partial lets us specify a “new” actionHow do we PROVE an incident was saved?The form needs to update the contents of the pop-up’s <div>Avalanche!How things works now...We could have an “Edit” link in the pop-upWe’ll start by modifying the “edit” actionSo why have two partials?And we’ll also need a new link on the show pageSo how do we use the link_to helper?Ajax links to the rescueWe’re using the wrong route!The HTTP method affects the route that’s chosenSo what’s an HTTP method?Head First Climbers needs you!Tools for your Rails Toolbox
10. Real-World Applications: Rails in the real world
Look! It’s a big Ruby “Try this” pageWeb apps need testing tooSo what kinds of tests are available?Unit testsFunctional testsIntegration testsGoing liveBut how do you switch between environments?So how do you change the database?What’s REST?So what are the main principles of REST?The web application that went astrayWhy is not being RESTful a problem?HTTP verbs are the only verbs you needLiving on the EdgeGetting more informationBuilt-in documentationA little light reading...The Ruby WayAgile Web Development with RailsRails CookbookHead First books on related topicsHead First AjaxHead First JavaScriptHead First Software DevelopmentTools for your Rails ToolboxLeaving town...It’s been great having you here in Railsville!
Index
About the Author
Copyright

Content preview from Head First Rails

Chapter 3. Inserting, Updating, and Deleting: Everything changes

Change is a fact of life—especially for data. So far you’ve seen how to whip up a quick Rails application with scaffolding, and how to write your own code to publish data from a database. But what if you want users to be able to edit data your way? What if scaffolding doesn’t do what you want? In this chapter, you’ll learn how to insert, update, and delete data in exactly the way you want. And while you’re doing that, you’ll be taken deeper into how Rails really works and maybe even learn a little about security along the way.

People want to post new ads online

People love the MeBay site, but there’s a problem. Because MeBay was nervous about people having too much access to the data, sellers have to phone in details of their items to MeBay and wait while the system administrators create new ads for the sellers. As the number of people sending in ads has grown, so has the wait time. A lot of people are taking their business to other advertising sites now.

So MeBay has relented. After some discussion, they’ve decided that people should be allowed to post their own ads on the site using a page that looks like this:

You already know how to build an app that publishes data from the database

The ads only go one way in the current ...

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