---
title: Traversing with Pagination
---

# Traversing with Pagination

{:toc}

The {{ site.data.variables.product.product_name }} API provides a vast wealth of information for developers to consume.
Most of the time, you might even find that you're asking for _too much_ information,
and in order to keep our servers happy, the API will automatically [paginate the requested items][pagination].

In this guide, we'll make some calls to the {{ site.data.variables.product.product_name }} Search API, and iterate over
the results using pagination. You can find the complete source code for this project
in the [platform-samples][platform samples] repository.

## Basics of Pagination

To start with, it's important to know a few facts about receiving paginated items:

1. Different API calls respond with different defaults. For example, a call to
[list GitHub's public repositories](https://developer.github.com/v3/repos/#list-all-public-repositories)
provides paginated items in sets of 30, whereas a call to the GitHub Search API
provides items in sets of 100
2. You can specify how many items to receive (up to a maximum of 100); but,
3. For technical reasons, not every endpoint behaves the same. For example,
[events](https://developer.github.com/v3/activity/events/) won't let you set a maximum for items to receive.
Be sure to read the documentation on how to handle paginated results for specific endpoints.

Information about pagination is provided in [the Link header](http://tools.ietf.org/html/rfc5988)
of an API call. For example, let's make a curl request to the search API, to find
out how many times Mozilla projects use the phrase `addClass`:

``` command-line
$ curl -I "{{ site.data.variables.product.api_url_pre }}/search/code?q=addClass+user:mozilla"
```

The `-I` parameter indicates that we only care about the headers, not the actual
content. In examining the result, you'll notice some information in the Link header
that looks like this:

    Link: <https://api.github.com/search/code?q=addClass+user%3Amozilla&page=2>; rel="next",
      <https://api.github.com/search/code?q=addClass+user%3Amozilla&page=34>; rel="last"

Let's break that down. `rel="next"` says that the next page is `page=2`. This makes
sense, since by default, all paginated queries start at page `1.` `rel="last"`
provides some more information, stating that the last page of results is on page `34`.
Thus, we have 33 more pages of information about `addClass` that we can consume.
Nice!

Keep in mind that you should **always** rely on these link relations provided
to you. Don't try to guess or construct your own URL. Some API calls, like [listing
commits on a repository][listing commits], use pagination results that are based
on SHA values, not numbers.

### Navigating through the pages

Now that you know how many pages there are to receive, you can start navigating
through the pages to consume the results. You do this by passing in a `page`
parameter. By default, `page` always starts at `1`. Let's jump ahead to page 14
and see what happens:

``` command-line
$ curl -I "https://api.github.com/search/code?q=addClass+user:mozilla&page=14"
```

Here's the link header once more:

    Link: <https://api.github.com/search/code?q=addClass+user%3Amozilla&page=15>; rel="next",
      <https://api.github.com/search/code?q=addClass+user%3Amozilla&page=34>; rel="last",
      <https://api.github.com/search/code?q=addClass+user%3Amozilla&page=1>; rel="first",
      <https://api.github.com/search/code?q=addClass+user%3Amozilla&page=13>; rel="prev"

As expected, `rel="next"` is at 15, and `rel="last"` is still 34. But now we've
got some more information: `rel="first"` indicates the URL for the _first_ page,
and more importantly, `rel="prev"` lets you know the page number of the previous
page. Using this information, you could construct some UI that lets users jump
between the first, previous, next, or last list of results in an API call.

### Changing the number of items received

By passing the `per_page` parameter, you can specify how many items you want
each page to return, up to 100 items. Let's try asking for 50 items about `addClass`:

``` command-line
$ curl -I "https://api.github.com/search/code?q=addClass+user:mozilla&per_page=50"
```

Notice what it does to the header response:

    Link: <https://api.github.com/search/code?q=addClass+user%3Amozilla&per_page=50&page=2>; rel="next",
      <https://api.github.com/search/code?q=addClass+user%3Amozilla&per_page=50&page=20>; rel="last"

As you might have guessed, the `rel="last"` information says that the last page
is now 20. This is because we are asking for more information per page about
our results.

## Consuming the information

You don't want to be making low-level curl calls just to be able to work with
pagination, so let's write a little Ruby script that does everything we've
just described above.

As always, first we'll require [GitHub's Octokit.rb][octokit.rb] Ruby library, and
pass in our [personal access token][personal token]:

``` ruby
require 'octokit'

# !!! DO NOT EVER USE HARD-CODED VALUES IN A REAL APP !!!
# Instead, set and test environment variables, like below
client = Octokit::Client.new :access_token => ENV['MY_PERSONAL_TOKEN']
```

Next, we'll execute the search, using Octokit's `search_code` method. Unlike
using `curl`, we can also immediately retrieve the number of results, so let's
do that:

``` ruby
results = client.search_code('addClass user:mozilla')
total_count = results.total_count
```

Now, let's grab the number of the last page, similar to `page=34>; rel="last"`
information in the link header. Octokit.rb support pagination information through
an implementation called "[Hypermedia link relations][hypermedia-relations]."
We won't go into detail about what that is, but, suffice to say, each element
in the `results` variable has a hash called `rels`, which can contain information
about `:next`, `:last`, `:first`, and `:prev`, depending on which result you're
on. These relations also contain information about the resulting URL, by calling
`rels[:last].href`.

Knowing this, let's grab the page number of the last result, and present all
this information to the user:

``` ruby
last_response = client.last_response
number_of_pages = last_response.rels[:last].href.match(/page=(\d+).*$/)[1]

puts "There are #{total_count} results, on #{number_of_pages} pages!"
```

Finally, let's iterate through the results. You could do this with a loop `for i in 1..number_of_pages.to_i`,
but instead, let's follow the `rels[:next]` headers to retrieve information from
each page. For the sake of simplicity, let's just grab the file path of the first
result from each page. To do this, we'll need a loop; and at the end of every loop,
we'll retrieve the data set for the next page by following the `rels[:next]` information.
The loop will finish when there is no `rels[:next]` information to consume (in other
words, we are at `rels[:last]`). It might look something like this:

``` ruby
puts last_response.data.items.first.path
until last_response.rels[:next].nil?
  last_response = last_response.rels[:next].get
  puts last_response.data.items.first.path
end
```

Changing the number of items per page is extremely simple with Octokit.rb. Simply
pass a `per_page` options hash to the initial client construction. After that,
your code should remain intact:

``` ruby
require 'octokit'

# !!! DO NOT EVER USE HARD-CODED VALUES IN A REAL APP !!!
# Instead, set and test environment variables, like below
client = Octokit::Client.new :access_token => ENV['MY_PERSONAL_TOKEN']

results = client.search_code('addClass user:mozilla', :per_page => 100)
total_count = results.total_count

last_response = client.last_response
number_of_pages = last_response.rels[:last].href.match(/page=(\d+).*$/)[1]

puts last_response.rels[:last].href
puts "There are #{total_count} results, on #{number_of_pages} pages!"

puts "And here's the first path for every set"

puts last_response.data.items.first.path
until last_response.rels[:next].nil?
  last_response = last_response.rels[:next].get
  puts last_response.data.items.first.path
end
```

## Constructing Pagination Links

Normally, with pagination, your goal isn't to concatenate all of the possible
results, but rather, to produce a set of navigation, like this:

![Sample of pagination links](/assets/images/pagination_sample.png)

Let's sketch out a micro-version of what that might entail.

From the code above, we already know we can get the `number_of_pages` in the
paginated results from the first call:

``` ruby
require 'octokit'

# !!! DO NOT EVER USE HARD-CODED VALUES IN A REAL APP !!!
# Instead, set and test environment variables, like below
client = Octokit::Client.new :access_token => ENV['MY_PERSONAL_TOKEN']

results = client.search_code('addClass user:mozilla')
total_count = results.total_count

last_response = client.last_response
number_of_pages = last_response.rels[:last].href.match(/page=(\d+).*$/)[1]

puts last_response.rels[:last].href
puts "There are #{total_count} results, on #{number_of_pages} pages!"
```

From there, we can construct a beautiful ASCII representation of the number boxes:
``` ruby
numbers = ""
for i in 1..number_of_pages.to_i
  numbers << "[#{i}] "
end
puts numbers
```

Let's simulate a user clicking on one of these boxes, by constructing a random
number:

``` ruby
random_page = Random.new
random_page = random_page.rand(1..number_of_pages.to_i)

puts "A User appeared, and clicked number #{random_page}!"
```

Now that we have a page number, we can use Octokit to explicitly retrieve that
individual page, by passing the `:page` option:

``` ruby
clicked_results = client.search_code('addClass user:mozilla', :page => random_page)
```

If we wanted to get fancy, we could also grab the previous and next pages, in
order to generate links for back (`<<`) and forward (`>>`) elements:

``` ruby
prev_page_href = client.last_response.rels[:prev] ? client.last_response.rels[:prev].href : "(none)"
next_page_href = client.last_response.rels[:next] ? client.last_response.rels[:next].href : "(none)"

puts "The prev page link is #{prev_page_href}"
puts "The next page link is #{next_page_href}"
```

[pagination]: /v3/#pagination
[platform samples]: https://github.com/github/platform-samples/tree/master/api/ruby/traversing-with-pagination
[octokit.rb]: https://github.com/octokit/octokit.rb
[personal token]: https://help.github.com/articles/creating-an-access-token-for-command-line-use
[hypermedia-relations]: https://github.com/octokit/octokit.rb#pagination
[listing commits]: https://developer.github.com/v3/repos/commits/#list-commits-on-a-repository
