Retrieving SUM(value) FROM a related table - cakephp

Question

I have a database table, lets say Person and each person has votes stored in a Vote table.
Each person will have many votes and some of these are up and some of these are down votes so I am not interested in COUNT.
I have the following query to retrieve votes for a single person:
$votes = $this->Vote->query("
SELECT IFNULL( SUM( value ) , 0 ) AS vote_count
FROM `votes`
WHERE person_id = {$person_id}");
Is it possible for me to fetch this information for a Person each time I call
$this->person->find("all")

Answer 1

This can be done using $virtualFields:
In the Vote model I add the following virtual field:
var $virtualFields = array(
'vote_count' => 'IFNULL( SUM( Vote.value ) , 0 )'
);
In the Person model I retrieve this every time by using the following $hasMany relationship:
var $hasMany = array('Vote' => array('fields' => array('vote_count')));
Note that by default it will always retrieve every field in the Vote table, this will result in retrieving the 'vote_count' SUM field by default and will only show one row as expected if you were to write out the query in full.
If you want to retrieve all of the rows and remove the SUM virtual field then you need to specify all the fields (as necessary) in the fields array except the 'vote_count' field e.g.
var $hasMany = array('Vote' => array('fields' => array('id', 'value')));
I would suggest this is better controlled by having a couple of functions in the Person model as such, which will allow you to decide on the fly how you want to retrieve the votes:
function allWithVoteCounts() {
$this->bindModel(array('hasMany' =>
array('Vote' => array(
'fields' => array('vote_count')
)
)
));
return $this->find('all');
}
function allVotes() {
$this->bindModel(array('hasMany' =>
array('Vote' => array(
'fields' => array('id', 'user_id', 'person_id', 'value', 'date')
)
)
));
return $this->find('all');
}
Then in the controller you can call:
$persons = $this->Person->allVotes();
or
$persons = $this->Person->allWithVoteCounts();