PHP API - Custom Object/Child Object Question

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We have built a custom object Entity_Data.Entities and related it to Contact (Entity = Parent, Contact = Child).

I have an existing Custom Script - PHP file that updates the Contact with various bits of information and now I am trying to add the Entity information to the process but I can’t figure out the syntax to expose that field on the Contact.

I am able to query the Entities object using the following query without issue:

$a_tbl = RNCPHP\ROQL::query("select id from entity_data.entities where entity_id = '".$_entity_id."'")->next();

Now when I try and use the ID value returned from the above query it fails saying column doesn’t exist.