The Booking sample app demonstrates:

  • 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

Browse Source

	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
			...

sqlite Installation

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

To install on OSX:

  1. Install Homebrew if you don’t already have it.
  2. Install pkg-config and sqlite3:
$ brew install pkgconfig sqlite3

To install on Ubuntu:

$ 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/examples/booking

Database / Gorp Plugin

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.

Interceptors

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

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)
}

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

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
}

Check out the user management code in app.go

Validation

The booking app does quite a bit of validation.

For example, here is the routine to validate a booking, from models/booking.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},
	)
}

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:

{{with $field := field "booking.CheckInDate" .}}
<p class="{{$field.ErrorClass}}">
    <strong>Check In Date:</strong>
    <input type="text" size="10" name="{{$field.Name}}" class="datepicker" value="{{$field.Flash}}">
    * <span class="error">{{$field.Error}}</span>
ss</p>
{{end}}

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

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