How to use the table columns instead of variables in QueryExpression::addCase() - mysql

Question

In CakePHPs new ORM, you can use the QueryBuilder to build (in theory) any query.
I want to select the value of one of two columns, depending on another value. In a regular query, that can be done as follows:
SELECT IF(from_id = 1, to_id, from_id) AS other_id FROM messages;
I am trying to archive the same query using the QueryBuilder and QueryExpression::addCase()
$messagesQuery = $this->Messages->find('all');
$messagesQuery->select([
'other_id' => $messagesQuery->newExpr()->addCase(
$messagesQuery->newExpr()->add(['from_id' => $this->authUser->id]),
['to_id', 'from_id'],
['integer', 'integer']
)
]);
This does not work, as the passed values are not integers, but rather table columns containing integers.
Through trial and error (using the method add() again), I got the following:
$messagesQuery = $this->Messages->find('all');
$messagesQuery->select([
'other_id' => $messagesQuery->newExpr()->addCase(
$messagesQuery->newExpr()->add(['from_id' => $this->authUser->id]),
[
$messagesQuery->newExpr()->add(['to_id']),
$messagesQuery->newExpr()->add(['from_id'])
],
['integer', 'integer']
)
]);
This results in the following query:
SELECT (CASE WHEN from_id = 1 THEN to_id END) AS `other_id` FROM messages Messages
Now, the ELSE part is missing, although the CakePHP book states:
Any time there are fewer case conditions than values, addCase will automatically produce an if .. then .. else statement.
The examples in the CakePHP book are not very helpful in this case, as they only use static integers or strings as values, for example:
#SELECT SUM(CASE published = 'Y' THEN 1 ELSE 0) AS number_published, SUM(CASE published = 'N' THEN 1 ELSE 0) AS number_unpublished FROM articles GROUP BY published
$query = $articles->find();
$publishedCase = $query->newExpr()->addCase($query->newExpr()->add(['published' => 'Y']), 1, 'integer');
$notPublishedCase = $query->newExpr()->addCase($query->newExpr()->add(['published' => 'N']), 1, 'integer');
$query->select([
'number_published' => $query->func()->sum($publishedCase),
'number_unpublished' => $query->func()->sum($unpublishedCase)
])
->group('published');
Is there a way to get the method addCase to use the two table columns as values instead of just static values?

Answer 1

As it turns out, I was just one logical step short of the solution in my previous edit.
As the CakePHP book correctly states:
Any time there are fewer case conditions than values, addCase will automatically produce an if .. then .. else statement.
For that to work though, both the conditions and values have to be an array, even if there is only one condition. (This the CakePHP book does not state.)
This code:
$messagesQuery = $this->Messages->find('all');
$messagesQuery->select([
'other_id' => $messagesQuery->newExpr()->addCase(
[
$messagesQuery->newExpr()->add(['from_id' => $this->authUser->id])
],
[
$messagesQuery->newExpr()->add(['to_id']),
$messagesQuery->newExpr()->add(['from_id'])
],
['integer', 'integer']
)
]);
results in this query:
SELECT (CASE WHEN from_id = 1 THEN to_id ELSE from_id END) AS `other_id` FROM messages Messages
Eureka