We use forms to collect information from users. Only by submitting this information to our application, and processing it, does our application start to become interesting.
<form>
</form>
A form must have an action attribute. The value of this attribute is the route/URL that the user should visit when the form is submitted.
<form action="/process_form">
</form>
Forms generally capture user input using <input>1 elements. Each <input> must be a child element of the form.
<form action="/process_form">
<input>
</form>
A <button> element is required to submit the form.
<form action="/process_form">
<input>
<button>Submit</button>
</form>
<input> attributesAt a minimum, each <input> needs a name attribute and a value attribute.
The value for the name attribute can be anything, but it should be unique within the form.
<!-- GOOD -->
<form action="/process_form">
<input name="email">
<input name="password">
<button>Submit</button>
</form>
<!-- BAD -->
<form action="/process_form">
<input name="email">
<input name="email">
<button>Submit</button>
</form>
By default the value attribute is empty, but it will automatically receive the text that the user typed into the field as the value.
You can also set an initial value for the value attribute. This is especially useful for “edit” forms.
<form action="/process_form">
<input name="email" value="[email protected]">
<button>Submit</button>
</form>
which renders in the browser like this:
Forms are used to collect information from our users and that information is sent to our app for processing. But how does our app know what the user typed in the form?
The query string is an optional part of a URL that begins with a ?. Since it’s optional, you can add a query string to the end of any URL:
http://www.example.com/?fruit=apple&color=green
A query string functions similar to a Ruby Hash— it’s a list of key-value pairs. In the example, fruit and color are keys, while apple and green are the values.
Forms are useful because they automatically create a query string when they are submitted. The keys in the resulting query string come from the name attribute of the <input> while the value comes from whatever the user typed into that field. The URL segment before the query string comes from the action attribute of the <form>.
<form action="http://www.example.com/">
<input name="fruit" value="apple">
<input name="color" value="green">
<button>Submit</button>
</form>
http://www.example.com/?fruit=apple&color=green
So when a form is submitted, the user is sent to the URL that was specified in the action attribute of the form. The name-value pairs from each input field inside the <form> element are added as a query string onto the URL from the action. Try it out!
In Rails, params is a special Hash that is defined every time someone visits a URL. Rails will first check to see if a query string is present and if it finds one, it adds any name/value pairs into a Ruby Hash. With the user input in a Hash we can more easily access and manipulate it in our application.
Assuming our application has a route defined for /add_fruit and a user submitted a form that resulted in visit to this URL:
/add_fruit?fruit=apple&color=green
Rails reads the query string and adds each name/value pair into the params Hash:
{"fruit" => "apple", "color" => "green"}
Try it out!
While the previous forms were all functional in that they created a query string with all of the information that a user filled out, they were technically invalid.
In order for a form to be considered valid by HTML standards, it must have a <label> element that is connected to each <input> element that the user interacts with.
First, add the <label> elements for each <input>:
<form action="/process_url">
<label>Fruit</label>
<input name="fruit">
<label>Color</label>
<input name="color">
<button>Submit</button>
</form>
Then, in order to connect one <label> to one <input>, both the <label> and <input> need an attribute with the same unique value.
The <label> element needs a for="" attribute while the <input> element needs an id="" attribute.
The value of these attributes can be anything, but remember it must be unique.
A complete valid form looks like this:
<form action="/process_url">
<label for="zebra">Fruit</label>
<input id="zebra" name="fruit">
<label for="giraffe">Color</label>
<input id="giraffe" name="color">
<button>Submit</button>
</form>
There are several reasons we need to write valid forms in our HTML:
rails grade will fail, since they won’t know how to fill out your forms.for="" and id="" attributes in order to understand how to fill out the form.<input> elements are one of the few HTML elements that don’t require a closing tag. ↩