# Friendly URLs

By default, Rails applications build URLs based on the primary key -- the `id` column from the database. Imagine we have a `Person` model and associated controller. We have a person record for `Bob Martin` that has `id` number `6`. The URL for his show page would be:

```
/people/6
```

But, for aesthetic or SEO purposes, we want Bob's name in the URL. The last segment, the `6` here, is called the "slug". Let's look at a few ways to implement better slugs.

## Simple Approach

The simplest approach is to override the `to_param` method in the `Person` model. Whenever we call a route helper like this:

```
person_path(@person)
```

Rails will call `to_param` to convert the object to a slug for the URL. If your model does not define this method then it will use the implementation in `ActiveRecord::Base` which just returns the `id`.

For this method to succeed, it's critical that all links use the `ActiveRecord` object rather than calling `id`. *Don't ever do this*:

```
person_path(@person.id) # Bad!
```

Instead, always pass the object:

```
person_path(@person)
```

### Slug Generation

Instead, in the model, we can override `to_param` to include a parameterized version of the person's name:

```ruby
class Person < ActiveRecord::Base
  def to_param
    [id, name.parameterize].join("-")
  end
end
```

For our user `Bob Martin` with `id` number `6`, this will generate a slug `6-bob_martin`. The full URL would be:

```
/people/6-bob-martin
```

The `parameterize` method from `ActiveSupport` will deal with converting any characters that aren't valid for a URL.

### Object Lookup

What do we need to change about our finders? Nothing! When we call `Person.find(x)`, the parameter `x` is converted to an integer to perform the SQL lookup. Check out how `to_i` deals with strings which have a mix of letters and numbers:

```irb
> "1".to_i
# => 1 
> "1-with-words".to_i
# => 1 
> "1-2345".to_i
# => 1 
> "6-bob-martin".to_i
# => 6 
```

The `to_i` method will stop interpreting the string as soon as it hits a non-digit. Since our implementation of `to_param` always has the `id` at the front followed by a hyphen, it will always do lookups based on just the `id` and discard the rest of the slug.

### Benefits

We've added content to the slug which will improve SEO and make our URLs more readable.