[wp-trac] [WordPress Trac] #43874: REST API: Only render fields specific to request when _fields= is used

[WordPress Trac]

#43874: REST API: Only render fields specific to request when _fields= is used
-----------------------------+------------------------------------
 Reporter:  danielbachhuber  |       Owner:  (none)
     Type:  defect (bug)     |      Status:  new
 Priority:  normal           |   Milestone:  4.9.6
Component:  REST API         |     Version:
 Severity:  normal           |  Resolution:
 Keywords:                   |     Focuses:  rest-api, performance
-----------------------------+------------------------------------

Comment (by schlessera):

 Some thoughts on the approach in https://github.com/WordPress/wordpress-
 develop/pull/12:

 **Possible minor scalability optimization for current approach:**

 If you `array_flip()` the array of fields at the start of the checks, you
 can turn the individual checks from a linear array search (`O(n)`) into a
 hash table lookup (`O(1)`). Probably not worth the hassle, as I doubt
 we'll have field arrays with thousands of fields.

 **Possible way to avoid code churn:**

 Turn the `$fields = get_fields_for_response()` into a `$schema =
 get_filtered_item_schema()`, so that all the checks remain unchanged.

 **Possible way to make the code cleaner - variant A (with even more code
 churn, though):**

 Iterate over the `$fields` and use a `switch` statement:
 {{{#!php
 foreach( $this->get_fields_for_response( $request ) as $field ) {
    switch ( $field ) {
         case 'id':
             $data['id'] = $user->ID;
             break;
         case 'username':
             $data['username'] = $user->user_login;
             break;
         // [...]
    }
 }
 }}}

 **Possible way to make the code cleaner - variant B (with yet more code
 churn):**

 Iterate over the `$fields` and map them to methods:
 {{{#!php
 public function prepare_item_for_response( $user, $request ) {
    // Could be deduced, but probably too much magic then.
    $mapping = array(
       'id'       => 'get_id',
       'username' => 'get_username'
    );

    foreach( $this->get_fields_for_response( $request ) as $field ) {
       if ( ! array_key_exists( $field, $mapping ) {
          // throw error
       }

       $method         = $mapping[ $field ];
       $data[ $field ] = $this->$method( $user, $request );
    }
 }

 private function get_id( $user, $request ) {
    return $user->ID;
 }

 private function get_username( $user, $request ) {
    return $user->user_login;
 }

 // [...]
 }}}

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Ticket URL: <https://core.trac.wordpress.org/ticket/43874#comment:3>
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