Entity query filter and sort

I don't know for sure but try this:

field_custom.reference__entity.field_number

the custom field name with __entity appended (double underscore) is a computed property.

Getting closer. that produces an error SQLSTATE[42S22]: Column not found: 1054 Unknown column 'node__field_custom.field_custom_'. Running through it with xdebug, I see that Drupal\Core\Entity\Query\Sql\Tables::addField is called with $field = "field_custom.reference__entity.field_number", it does its bits to figure out the tables to join, but early on it runs $column = $field_storage->getMainPropertyName(); which returns null, so when it gets down to $sql_column = $table_mapping->getFieldColumnName($field_storage, $column);, inside that method the column name is getting appended as null since there isn't a primary property.
$column_name = !in_array($property_name, $this->getReservedColumns()) ? $field_name . '_' . $property_name : $property_name;

So I see where its breaking and technically why, but not sure how to resolve it. Will attack it more tomorrow.

Ahh, yeah theres no main property on custom fields. Relationships are supported in views if you can go that route. The dot notation stuff on referenced entities I guess is specific for entity references at the field level. So you would otherwise probably have to go with the database api select query.

I was able to figure this out with your feedback digging through web/core/lib/Drupal/Core/Entity/Query/Sql/Tables.php with xdebug. The end string I used was field_custom.reference.reference__entity:node.field_number

When this is broken in to specifiers for join tables:
- field_custom is used as the base table
- Although the main property is null, since the next specifier reference is a real column it takes precedence and the key is advanced
- reference__entity:node is next and is used as the relationship_specifier. Since it's in the property definitions and is type DataReferenceDefinitionInterface, it joins the node table.
- Works as expected from here with field_number

I'm going to mark this works as designed, but it would be great to get this documented in some examples somewhere. I'm not sure the best place to put it. A new page under https://www.drupal.org/docs/extending-drupal/contributed-modules/contrib... → ?

Oh wow, thats awesome news! Yes, if you would create a new page there, that would be perfect and appreciated!

@mrconnerton, I created a documentation page. Can you review this and improve if needed?

https://www.drupal.org/docs/extending-drupal/contributed-modules/contrib... →