go-simple-news-aggregator

go-simple-news-aggregator

The 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

Database Install and Setup

This example used sqlite, (Alternatively can use mysql, postgres, etc.)

sqlite Installation

• The article app uses go-sqlite3 database driver, which depends on the C library

Install sqlite on OSX:

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

$ brew install pkgconfig sqlite3

Install sqlite on Ubuntu:

$ sudo apt-get install sqlite3 libsqlite3-dev

Once SQLite is installed, it will be possible to run the article app:

	$ revel run github.com/PROger4ever/go-simple-news-aggregator

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, Article, and Source tables, and insert some test records.
• BeforeRequest - Begins a transaction and stores the Transaction on the Controller
• AfterRequest - Commits the transaction, or panics if there was an error.
• OnException - Rolls back the transaction

Interceptors

app/controllers/init.go registers the interceptors that runs before each action:

func init() {
	revel.OnAppStart(Init)
	revel.InterceptMethod((*GorpController).Begin, revel.BEFORE)
	revel.InterceptMethod(Application.AddUser, revel.BEFORE)
	revel.InterceptMethod(Sources.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 do not have a session cookie.

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

Validation

The article app does quite a bit of validation.

Revel applies the validation and records errors using the name of the validated variable (unless overridden).

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