CODEWITHSUNDEEP
phplimitoffsetmusicbrainz
Ɛɔıs3
Ɛɔıs3

Reputation: 7853

Manage with limit and offset in php

I am currently developing a web application that will find artists and their associates titles. To do this, I decided to parse the API MusicBrainz, through this package (which documentation is here).

Suppose I already have the artist mbid (unique identifier for MusicBrainz).

The problem is that if I do a search on David Guetta (mbid = 302bd7b9-d012-4360-897a-93b00c855680) for example, the script tells me that the number of releases is 196. However, the API provides 100 maximum results per request.

// Instantiate a MusicBrainz object
$brainz = new MusicBrainz(new GuzzleHttpAdapter(new Client()));
$brainz->setUserAgent('ApplicationName', '0.2', 'http://example.com');

$limit = 100;
$offset = 0;

$includes = array('labels', 'recordings');
try {
  $details = $brainz->browseRelease('artist', '302bd7b9-d012-4360-897a-93b00c855680', $includes, $limit, $offset);
  print_r($details);
} catch (Exception $e) {
  print $e->getMessage();
}

The function browseRelease below allows us to define such parameters as limit and offset.

public function browseRelease($entity, $mbid, $includes = array(), $limit = 25, $offset = null, $releaseType = array(), $releaseStatus = array())
{
  if (!in_array($entity, array('artist', 'label', 'recording', 'release-group'))) {
    throw new Exception('Invalid browse entity for release');
  }
  return $this->browse(
    new Filters\ReleaseFilter(array()),
      $entity,
      $mbid,
      $includes,
      $limit,
      $offset,
      $releaseType,
      $releaseStatus
  );
}

Now we come to my real question in this post.

If I defined $limit = 100 and $offset = 0 for the first query, I don't understand how to change these values depending on the number of total releases, and thus get the results that are between 100 and 196 (in this example).

Upvotes: 1

Views: 6157

Answers (2)

JonnyJD
JonnyJD

Reputation: 2643

The pseudo code answer from Jordumus is correct, but this is how you have to modify your code to make it work.

$limit = 100;
$offset = 0;
$release_count = 0;

$includes = array('labels', 'recordings');
do {
  if ($offset != 0) sleep(1);
  try {
    $details = $brainz->browseRelease('artist', '302bd7b9-d012-4360-897a-93b00c855680', $includes, $limit, $offset);
    $release_count = $details['release-count'];
    print_r($details);
  } catch (Exception $e) {
    print $e->getMessage();
  }
  $offset += $limit;
} while ($offset < $release_count);

Note that it would be enough to set $release_count the first time, since the value doesn't change, but resetting it also doesn't hurt.

I added a sleep in there because of the required rate limiting which doesn't seem to be implemented in the PHP library.

Upvotes: 1

Jordumus
Jordumus

Reputation: 2783

As of this question, I'll post my answer as a "real answer":

Pseudolanguage

Given: 150 results. You can define: offset and limit. But: max limit is 100 results.

You'll need 2 calls, because you can only get 100 results at a time. This is how you could solve it:

Call 1:

Offset: 0
Limit: 100
//Returns results 0 to 99.

Call 2:

Offset: 100
Limit: [OPTIONAL] 100
//Returns resuls 100 to 199. As there are only 150 results in total, it will automatically return 100 to 150

Now, we could also make this automatic with a loop:

limit = 100
for (var i = 0; i < maxResults; i=i+100)
{
    offset = i
    GetResults(offset,limit);
}

Upvotes: 2

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