Add custom column to post list table

Question

I have a custom post type called Book and I want to add the publisher and book author custom columns in the edit page.

I also want to fetch a specific value from each fields (I created two fields for the above columns) to display in those two additional columns. I actually can display with this code below but the point is I have to declare variable (for example: the $value variable) for each data.

So could you please share me some ideas to display that with loop or somethings.

add_filter( 'manage_book_posts_columns', 'set_custom_edit_book_columns' );
add_action( 'manage_book_posts_custom_column' , 'custom_book_column', 10, 2 );

function set_custom_edit_book_columns($columns) {
    $value = get_field( "contact_person" );
    unset( $columns['author'] );
    $columns['book_author'] = __( 'Author', 'your_text_domain' );
    $columns['publisher'] = __( 'Publisher', 'your_text_domain' );

    return $columns;
}

function custom_book_column( $column, $post_id ) {
    switch ( $column ) {

        case 'book_author' :
            $value = get_field( "contact_person" );
            $terms = get_the_term_list( $post_id , '$value' , '' , ',' , '' );
            if ( is_string( $value ) )
                echo $value;
            else
                _e( 'Unable to get author(s)', 'your_text_domain' );
            break;

        case 'publisher' :
            echo get_post_meta( $post_id , 'publisher' , true ); 
            break;

    }
}

Answer 1

Maybe you just need to change it to:

case 'book_author' :
    $value = get_field( "contact_person", $post_id );

The second parameter is probably needed as it is in a loop, but not The Loop.