title	The 'Hello World' app
layout	tutorial

This page runs through the quick exercise of implementing a "Hello World" application.

Let's start with the myapp project that was created previously.

Edit the app/views/App/Index.html template to add this form, under the included flash.html template:

<form action="/App/Hello" method="GET">
    <input type="text" name="myName" /><br/>
    <input type="submit" value="Say hello!" />
</form>

Refresh the page to see our work.

Enter some data and submit the form.

That makes sense. Add the method to app/controllers/app.go: {% highlight go %} func (c App) Hello(myName string) revel.Result { return c.Render(myName) } {% endhighlight %}

Next, we have to create the view. Create a file app/views/App/Hello.html, with this content:

{% capture ex %}{% raw %} {{set . "title" "Hello page"}} {{template "header.html" .}}

Hello {{.myName}}

Back to form

{{template "footer.html" .}} {% endraw %}{% endcapture %} {% highlight htmldjango %}{{ex}}{% endhighlight %}

Finally, add the following to conf/routes file, just below the App.Index entry.

{% capture ex %}{% raw %} GET /App/Hello App.Hello {% endraw %}{% endcapture %} {% highlight htmldjango %}{{ex}}{% endhighlight %}

Refresh the page, and you should see a greeting:

Lastly, let's add some validation. The name should be required, and at least three characters.

To do this, let's use the validation module. Edit your method in app/controllers/app.go: {% highlight go %} func (c App) Hello(myName string) revel.Result { c.Validation.Required(myName).Message("Your name is required!") c.Validation.MinSize(myName, 3).Message("Your name is not long enough!")

if c.Validation.HasErrors() {
    c.Validation.Keep()
    c.FlashParams()
    return c.Redirect(App.Index)
}

return c.Render(myName)

} {% endhighlight %}

Now it will send the user back to Index() if they have not entered a valid name. Their name and the validation error are kept in the Flash, which is a temporary cookie.

The provided flash.html template will show any errors or flash messages:

{% capture ex %}{% raw %} {{if .flash.success}}

{{.flash.success}}

{{end}}

{{if or .errors .flash.error}}

{{if .flash.error}} {{.flash.error}} {{end}} {{if .errors}}

{{range .errors}}
• {{.}}
{{end}}

{{end}}

{{end}} {% endraw %}{% endcapture %} {% highlight htmldjango %}{{ex}}{% endhighlight %}

When we submit that form with a name that fails validation, we want the form to retain the bad name, so that the user can edit it before re-submitting. Amend the form you had added to your app/views/App/Index.html template:

{% capture ex %}{% raw %}

{{with $field := field "myName" .}}
{{end}} {% endraw %}{% endcapture %} {% highlight htmldjango %}{{ex}}{% endhighlight %}

Now when we submit a single letter as our name:

Success, we got an appropriate error and our input was saved for us to edit.

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• Read more in the manual
• Look at the example applications