Exporting Data for Offline Processing

In this recipe we will learn how to use the export API to extract data and process it with PHP. At the end of the recipe you can download the complete PHP script.

Note: The following recipe is written using an ArangoDB server with version 2.6 or higher. You can also use the devel branch, since version 2.6 hasn’t been an official release yet.

Howto

Importing example data

First of all we need some data in an ArangoDB collection. For this example we will use a collection named users which we will populate with 100.000 example documents. This way you can get the data into ArangoDB:

# download data file
wget https://jsteemann.github.io/downloads/code/users-100000.json.tar.gz
# uncompress it
tar xvfz users-100000.json.tar.gz
# import into ArangoDB 
arangoimp --file users-100000.json --collection users --create-collection true

Setting up ArangoDB-PHP

For this recipe we will use the ArangoDB PHP driver:

git clone -b devel "https://github.com/arangodb/arangodb-php.git"

We will now write a simple PHP script that establishes a connection to ArangoDB on localhost:

<?php

namespace triagens\ArangoDb;

// use the driver's autoloader to load classes
require 'arangodb-php/autoload.php';
Autoloader::init();

// set up connection options
$connectionOptions = array(
    // endpoint to connect to
    ConnectionOptions::OPTION_ENDPOINT     => 'tcp://localhost:8529',
    // can use Keep-Alive connection
    ConnectionOptions::OPTION_CONNECTION   => 'Keep-Alive',
    // use basic authorization
    ConnectionOptions::OPTION_AUTH_TYPE    => 'Basic',
    // user for basic authorization
    ConnectionOptions::OPTION_AUTH_USER    => 'root',
    // password for basic authorization
    ConnectionOptions::OPTION_AUTH_PASSWD  => '',
    // timeout in seconds
    ConnectionOptions::OPTION_TIMEOUT      => 30,
    // database name 
    ConnectionOptions::OPTION_DATABASE     => '_system'
    );

try {
  // establish connection
  $connection = new Connection($connectionOptions);

  echo 'Connected!' . PHP_EOL;

  // TODO: now do something useful with the connection!

} catch (ConnectException $e) {
  print $e . PHP_EOL;
} catch (ServerException $e) {
  print $e . PHP_EOL;
} catch (ClientException $e) {
  print $e . PHP_EOL;
}

After running the script you should see Connected! in the bash if successful.

Extracting the data

Now we can run an export of the data in the collection users. Place the following code into the TODO part of the first code:

function export($collection, Connection $connection) {
  $fp = fopen('output.json', 'w');

  if (! $fp) {
    throw new Exception('could not open output file!');
  }

  // settings to use for the export
  $settings = array(
      'batchSize' => 5000,  // export in chunks of 5K documents
      '_flat' => true       // use simple PHP arrays
      );

  $export = new Export($connection, $collection, $settings);

  // execute the export. this will return an export cursor
  $cursor = $export->execute();

  // statistics
  $count   = 0;
  $batches = 0;
  $bytes   = 0;

  // now we can fetch the documents from the collection in batches
  while ($docs = $cursor->getNextBatch()) {
    $output = '';
    foreach ($docs as $doc) {
      $output .= json_encode($doc) . PHP_EOL;
    }

    // write out chunk
    fwrite($fp, $output);

    // update statistics
    $count += count($docs);
    $bytes += strlen($output);
    ++$batches;
  }

  fclose($fp);

  echo sprintf('written %d documents in %d batches with %d total bytes',
      $count,
      $batches,
      $bytes) . PHP_EOL;
}

// run the export
export('users', $connection);

The function extracts all documents from the collection and writes them into an output file output.json. In addition it will print some statistics about the number of documents and the total data size:

written 100000 documents in 20 batches with 40890013 total bytes

Applying some transformations

We now will use PHP to transform data as we extract it:

function transformDate($value) {
  return preg_replace('/^(\\d+)-(\\d+)-(\\d+)$/', '\\2/\\3/\\1', $value);
}

function transform(array $document) {
  static $genders = array('male' => 'm', 'female' => 'f');

  $transformed = array(
      'gender'      => $genders[$document['gender']],
      'dob'         => transformDate($document['birthday']),
      'memberSince' => transformDate($document['memberSince']),
      'fullName'    => $document['name']['first'] . ' ' . $document['name']['last'],
      'email'       => $document['contact']['email'][0]
      );

  return $transformed;
}

function export($collection, Connection $connection) {
  $fp = fopen('output-transformed.json', 'w');

  if (! $fp) {
    throw new Exception('could not open output file!');
  }

  // settings to use for the export
  $settings = array(
      'batchSize' => 5000,  // export in chunks of 5K documents
      '_flat' => true       // use simple PHP arrays
      );

  $export = new Export($connection, $collection, $settings);

  // execute the export. this will return an export cursor
  $cursor = $export->execute();

  // now we can fetch the documents from the collection in batches
  while ($docs = $cursor->getNextBatch()) {
    $output = '';
    foreach ($docs as $doc) {
      $output .= json_encode(transform($doc)) . PHP_EOL;
    }

    // write out chunk
    fwrite($fp, $output);
  }

  fclose($fp);
}

// run the export
export('users', $connection);

With this script the following changes will be made on the data:

  • rewrite the contents of the genderattribute. female becomes f and male becomes m
  • birthday now becomes dob
  • the date formations will be changed from YYYY-MM-DD to MM/DD/YYYY
  • concatenate the contents of name.first and name.last
  • contact.email will be transformed from an array to a flat string
  • every other attribute will be removed

Note: The output will be in a file named output-transformed.json.

Filtering attributes

Exclude certain attributes

Instead of filtering out as done in the previous example we can easily configure the export to exclude these attributes server-side:

// settings to use for the export
$settings = array(
  'batchSize' => 5000,  // export in chunks of 5K documents
  '_flat' => true,      // use simple PHP arrays
  'restrict' => array(
    'type' => 'exclude',
    'fields' => array('_id', '_rev', '_key', 'likes')
  )
);

This script will exclude the attributes _id, _rev. _key and likes.

Include certain attributes

We can also include attributes with the following script:

function export($collection, Connection $connection) {
  // settings to use for the export
  $settings = array(
      'batchSize' => 5000,  // export in chunks of 5K documents
      '_flat' => true,      // use simple PHP arrays
      'restrict' => array(
        'type' => 'include',
        'fields' => array('_key', 'name')
        )
      );

  $export = new Export($connection, $collection, $settings);

  // execute the export. this will return an export cursor
  $cursor = $export->execute();

  // now we can fetch the documents from the collection in batches
  while ($docs = $cursor->getNextBatch()) {
    $output = '';

    foreach ($docs as $doc) {
      $values = array(
          $doc['_key'],
          $doc['name']['first'] . ' ' . $doc['name']['last']
          );

      $output .= '"' . implode('","', $values) . '"' . PHP_EOL;
    }

    // print out the data directly 
    print $output;
  }
}

// run the export
export('users', $connection);

In this script only the _key and name attributes are extracted. In the prints the _key/name pairs are in CSV format.

Note: The whole script can be downloaded.

Using the API without PHP

The export API REST interface can be used with any client that can speak HTTP like curl. With the following command you can fetch the documents from the users collection:

curl
  -X POST
  http://localhost:8529/_api/export?collection=users
--data '{"batchSize":5000}'

The HTTP response will contatin a result attribute that contains the actual documents. The attribute hasMore will indicate if there are more documents for the client to fetch. The HTTP will also contain an attribute id if set to true.

With the id you can send follow-up requests like this:

curl
  -X PUT
  http://localhost:8529/_api/export/13979338067709

Authors: Thomas Schmidts, Jan Steemann

Tags: #howto #php