How do I set the value of a custom entries order field from a plugin? I'm trying to set the value of a custom field on an order when saving an entry. I found an example of how to do this for a simple text field, but the field I'm trying to set is an entries field, not just a text field. I've attempted to set the value using the following code in my entries.saveEntry event. I'm assuming I'm doing this wrong since this is an entries field, not a simple text field, but I don't know the syntax for setting content on an entries field.

$cart = craft()-&gt;commerce_cart-&gt;getCart();
$cart-&gt;setContentFromPost(['entriesFieldHandle' =&gt; $entry-&gt;id]);
I was close. I was correct in assuming my syntax was incorrect for setting the value of an entries field.

Since an entries field is an array of elements, not just a single element, I just needed to set the value of the field as an array instead of a string.

Changing 

$cart-&gt;setContentFromPost(['entriesFieldHandle' =&gt; $entry-&gt;id]);


to

$cart-&gt;setContentFromPost(['entriesFieldHandle' =&gt; [$entry-&gt;id]]);


seemed to do the trick.

To zoom in a little more, the value needs to be set with 'entriesFieldHandle' =&gt; [$entry-&gt;id] instead of 'entriesFieldHandle' =&gt; $entry-&gt;id.