The Booking sample app demonstrates (browse the source):

• Using an SQL (SQLite) database and configuring the Revel DB module.

• Using the third party GORP ORM-ish library

• Interceptors for checking that an user is logged in.

• Using validation and displaying inline errors

  booking/app/ models # Structs and validation. booking.go hotel.go user.go

    controllers
    	init.go    # Register all of the interceptors.
    	gorp.go    # A plugin for setting up Gorp, creating tables, and managing transactions.
    	app.go     # "Login" and "Register new user" pages
    	hotels.go  # Hotel searching and booking
  
    views
    	...
  

The booking app uses go-sqlite3 database driver (which wraps the native C library).

1. Install Homebrew if you don't already have it.
2. Install pkg-config and sqlite3:

$ brew install pkgconfig sqlite3

$ sudo apt-get install sqlite3 libsqlite3-dev

Once you have SQLite installed, it will be possible to run the booking app:

$ revel run github.com/revel/samples/booking

app/controllers/gorp.go defines GorpPlugin, which is a plugin that does a couple things:

• OnAppStart: Uses the DB module to open a SQLite in-memory database, create the User, Booking, and Hotel tables, and insert some test records.
• BeforeRequest: Begins a transaction and stores the Transaction on the Controller
• AfterRequest: Commits the transaction. Panics if there was an error.
• OnException: Rolls back the transaction.

app/controllers/init.go registers the interceptors that run before every action:

{% highlight go %} func init() { revel.OnAppStart(Init) revel.InterceptMethod((*GorpController).Begin, revel.BEFORE) revel.InterceptMethod(Application.AddUser, revel.BEFORE) revel.InterceptMethod(Hotels.checkUser, revel.BEFORE) revel.InterceptMethod((*GorpController).Commit, revel.AFTER) revel.InterceptMethod((*GorpController).Rollback, revel.FINALLY) } {% endhighlight %}

As an example, checkUser looks up the username in the session and redirects the user to log in if they are not already.

{% highlight go %} func (c Hotels) checkUser() revel.Result { if user := c.connected(); user == nil { c.Flash.Error("Please log in first") return c.Redirect(Application.Index) } return nil } {% endhighlight %}

Check out the user management code in app.go

The booking app does quite a bit of validation.

For example, here is the routine to validate a booking, from models/booking.go:

{% highlight go %} func (booking Booking) Validate(v *revel.Validation) { v.Required(booking.User) v.Required(booking.Hotel) v.Required(booking.CheckInDate) v.Required(booking.CheckOutDate)

v.Match(b.CardNumber, regexp.MustCompile(`\d{16}`)).
	Message("Credit card number must be numeric and 16 digits")

v.Check(booking.NameOnCard,
	revel.Required{},
	revel.MinSize{3},
	revel.MaxSize{70},
)

} {% endhighlight %}

Revel applies the validation and records errors using the name of the validated variable (unless overridden). For example, booking.CheckInDate is required; if it evaluates to the zero date, Revel stores a ValidationError in the validation context under the key "booking.CheckInDate".

Subsequently, the Hotels/Book.html template can easily access them using the field helper:

{% capture ex %}{% raw %} {{with $field := field "booking.CheckInDate" .}}

Check In Date: * {{$field.Error}} ss

The field template helper looks for errors in the validation context, using the field name as the key.