Defining global conditions in Model

Question

Is it possible to define global conditions for Model ?

I have 2 Models: User and Student. In database both of them are using table u

Answer 1

Use beforeFind

You can use before find to modify all queries issued for a model:

function beforeFind(array $queryData) {
    $queryData['conditions'][]['NOT'][$this->alias . '.parent_id'] = null;
    return $queryData;
}

Be careful using this technique to not overwrite existing conditions (note the extra []) otherwise a query for "not parent_id 2" becomes "not parent_id null".