First of all, thanks for your answer.
// relationship field => ID values
array(
'key' => 'relationship_field_name',
'value' => '"'.$post_id.'"',
'compare' => 'LIKE'
),
lets suppose that there is a posts with IDs 16, 161, 616 and the post that I want to search is 16, wouldn’t this search cause problems? By problems I mean giving wrong results back.
I also think that it is not a good practice to store the ids in a serialized array, so I’m working on a code that stores data adding each ID separated, but I would like to know your opinion. Thanks again John.