查询由post_object自定义字段过滤的帖子

I am trying to query any post which has a certain post_object selected as its "parent". The parent value will have to match the ID of the current post. I have been able to replicate this functionality by querying all posts of this post type and then comparing the values within the loop, like so:

<?php
    $wp_query = new WP_Query();
    $wp_query->query(  array (
        'post_type' => 'my_post_type',
        'meta_key'=>'post_object_field'
)); 

if ( have_posts() ) : while ( have_posts() ) : the_post(); ?>

    <?php 
    $parent = get_field('post_object_field'); 
    $parentId = $parent->ID; ?>

    <?php if ($postId == $parentId): ?>

        // content 

    <?php endif; ?>
<?php endwhile; endif; ?>

I'm wonder if there is a way to check for this value inside the query, and if so, if it's any faster or more correct.

To get all the posts/pages that are children of a given post/page, you can use the parameter post_parent, using the ID of the parent post.

For example, if you have a post

$wp_query->query(  array (
    'post_type'    => $children_post_type
    'post_parent'  => $postId
)); 

And of course, yes, performing a query will be much more efficient than performing a query + getting a field value + creating a variable + looping the results making a comparison...

EDIT: According to your comments, it seems that you're actually trying to get all those posts that have a given value in a custom field of type Post Object. This field contains a number, which is the ID of the post it relates to, so you just need to add a parameter meta_value_num in your query:

$wp_query->query(  array (
    'post_type'      => 'my_post_type',
    'meta_key'       => 'post_object_field'
    'meta_value_num' => $postId
));

This will retrieve all the posts that have a custom field called post_object_field with a value $postId.

EDIT: Try this:

$args = array(
'post_type'  => 'my_post_type',
'meta_query' => array(
    array(
        'key'     => 'post_object_field',
        'value'   => $postId,
        'compare' => '='
    )
)
);

I was able to filter the results within the query using:

<?php
    $wp_query = new WP_Query();
    $wp_query->query(  array (
        'post_type' => 'my_post_type',
        'meta_query' => array(
            array(
                'key' => 'post_object_field',
                'value' => $postId,
                'compare' => '=='
            )
         )
    )); 

if ( have_posts() ) : while ( have_posts() ) : the_post(); ?>

    // content 

<?php endwhile; endif; ?>

<?php
$wp_query = new WP_Query();
$wp_query->query(  array (
    'post_type' => 'my_post_type',
    'meta_query' => array(
        array(
            'key' => 'post_object_field',
            'value' => $postId,
            'compare' => '=='
        )
     )
)); 

if ( have_posts() ) : while ( have_posts() ) : the_post(); ?>

// content 

enter code here