Added Elasticsearch::get_documents and Indexable::multi_get

[brandon-m-skinner]

Description of the Change

We needed an easy way to fetch multiple documents per API call, so we added get_documents to the Elasticsearch class and then added multi_get to the Indexable class for ease of use.

Props @nickdaugherty
cc: @rinatkhaziev @pschoffer @netsuso @parkcityj

Alternate Designs

N/A

Benefits

Allows you to get multiple documents per API call.

Possible Drawbacks

N/A

Verification Process

We tested in manually and then started using it in functionality for our search offering which has been running on large sites for months now.

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests passed.

Applicable Issues

Changelog Entry

Added Elasticsearch::get_documents and Indexable::multi_get. Props @nickdaugherty

[tlovett1]

@brandon-m-skinner will this only work with ES 7.0+?

[brandon-m-skinner]

5.0 and higher

[felipeelia]

Unfortunately, this doesn't work with Elasticsearch 5. To have it working on versions older than 7, we'll have to replicate the code we have here and in some other parts of this same class. Something like this:

if ( version_compare( $this->get_elasticsearch_version(), '7.0', '<' ) ) {
	$path = apply_filters( 'ep_index_' . $type . '_request_path', $index . '/' . $type . '/_mget', $document_ids, $type );
} else {
	$path = apply_filters( 'ep_index_' . $type . '_request_path', $index . '/_doc/_mget', $document_ids, $type );
}

It'll also be needed to pass the $type as a parameter to the get_documents method. Something like:

return Elasticsearch::factory()->get_documents( $this->get_index_name(), $this->slug, $object_ids );

Would it be possible to have these changes applied to this PR, @brandon-m-skinner? Thanks!

[felipeelia]

Closing it in favor or #2210. Thanks!