Save Gravity Form field data to post meta by adding a class to the field.

gf-map-class-to-post-meta.php

<?php
/**
 * Save Gravity Form field data to post meta by adding a class to any field.
 * Meta is mapped so that it is readable by Advanced Custom Fields
 * Format class as…
 * post_meta-{meta_key}						-- for simple fields & writing lists as array to single meta record
 * post_meta-{meta_key}-.3					-- for multi-input fields
 * post_meta-{repeater_key}-1.{meta_key}	-- for list fields mapped to meta readable by ACF
 */
// Run this function after the Gravity Form has created a post
add_action( 'gform_after_create_post', function( $post_id, $entry, $form ) {

	// Loop through the forms fields
	foreach( $form['fields'] as &$field ) {

		// If class does not call a post_meta save, then ignore it.
        if ( strpos( $field['cssClass'], 'post_meta-' ) === false )
            continue;

		// Find all post_meta save calls within the class
		preg_match_all( '/post_meta-[\S]+/', $field['cssClass'], $post_meta_save_calls );

		// Loop through the post_meta save calls
		foreach ( $post_meta_save_calls[0] as $i => $post_meta_save_call ) {

			// Remove the post_meta- identifier
			$post_meta = str_replace( 'post_meta-', '', $post_meta_save_call );

			// Find any complex GF to post_meta mapping and do things if any exist
			if ( preg_match( '/-\.\d+/', $post_meta, $complex_post_meta_mapping ) ) {

				// Get the Gravity Form input identifier and the post meta key
				$post_meta_map = explode( '-', $post_meta );

				// Add the post meta for the complex mapping
				add_post_meta( $post_id, $post_meta_map[0], $entry[ $field['id'] . $post_meta_map[1] ], true );

			} else {

				// Check the type of Gravity Form field and process accordingly
				switch ( $field['type'] ) {

					case 'list':

						// Get the Gravity form value for this list and maybe_unserialize it
						$value = maybe_unserialize( $entry[ $field['id'] ] );

						// If columns have been identified, then process meta to be readable by ACF
						if ( preg_match( '/-\d+\./', $post_meta, $complex_post_meta_mapping ) ) {

							// Count how many rows are in the list
							$count = count( $value );

							// Get the Gravity Form column identifiers and the post meta key
							$post_meta_map = explode( '-', $post_meta );

							// Pull the top-level meta key from the array, leaving column meta keys
							$post_meta_key = array_shift( $post_meta_map );

							// initalize column key array
							$column_keys = array();

							// Populate column key array
							foreach ( $post_meta_map as $column ) {

								$column = explode( '.', $column );

								$key = (int) $column[0] - 1;

								$column_keys[] = $column[1];

							}

							// If multiple column list
							if ( ! is_null( $value ) && is_array( $value[0] ) ) {

								foreach ( $value as $row_key => $row ) {

									$row = array_values( $row );

									foreach ( $row as $column_key => $data ) {

										add_post_meta( $post_id, $post_meta_key . '_' . $row_key . '_' . $column_keys[ $column_key ], $data, true );

									}

								}

							// If single column list
							} else if ( ! is_null( $value ) ) {

								foreach ( $value as $row_key => $data ) {

									add_post_meta( $post_id, $post_meta_key . '_' . $row_key . '_' . $column_keys[0], $data, true );

								}

							}

							// Add count of rows, so ACF can properly read the meta data
							add_post_meta( $post_id, $post_meta_key, $count, true );

						} else {

							// If we've not defined column keys, then simply write the list data as an array to a single meta record
							add_post_meta( $post_id, $post_meta, $value, true );

						}

						break;

					case 'checkbox':

						$value = array();

						// Loop through the Gravity Forms entry
						foreach ( $entry as $key => $data ) {

							// If entry record is an option belonging to specific checkbox field then add it to our value array
						    if ( strpos( (string) $key, (string) $field['id'] ) === 0 ) {

						        $value[ $key ] = $data;

						    }

						}

						// Re-index the array
						$value = array_values( $value );

						// Add the post meta
						add_post_meta( $post_id, $post_meta, $value );

						break;

					default:

						// Add the post meta for non-complex mapping
						add_post_meta( $post_id, $post_meta, $entry[ $field['id'] ], true );

						break;

				}

			}

		}

    }

	return $form;

}, 10, 3 );