How to fetch out complex result from the database - Yii - yii

Question

i am facing problem to fetch out records from table using Yii relationship,
i have 3 tables
1) Students -> ID, Name, Roll_Number
2) Subjects -> ID, Name
3) Students_taken_Subjects -> ID, Student_ID, Subject_ID
Suppose there are number of students have taken more than one subjects which are stored in the 3rd table "Students_taken_Subjects" then how i can fetch out the list of students taken any specific subject?
e.g. list of students taken maths
which one from below relationships are correct and how can i get results into the $dataProvider variable?
'Students'=>array(self::HAS_MANY, 'Subjects', 'Student_ID'),
and
return array(
'Students'=>array(self::MANY_MANY, 'Subjects',
'Students_taken_Subjects(student_id, subject_id)'),
);

Answer 1

The relationship between Subjects and Students is MANY_MANY, but you've written it a bit wrong, This is what you need:
class Subjects extends CActiveRecord
{
// ...
public function relations()
{
return array(
'Students'=>array(self::MANY_MANY, 'Students', 'Students_taken_Subjects(Subject_ID, Student_ID)'),
);
}
// ...
}
Once you've written this relation, the Subjects active record will have a Students property that returns an array with the 0 or more students taking that subject. You can access them like this:
$subject = Subjects::model()->findByPk($pk);
$students = $subject->Students; // an array with the subject's students
The above code will result in two DB accesses, one for the $subject and one for the related $students. This might be fine, but if you are accessing a lot of subjects it could become a problem with too much "lazy loading". You can tell Yii to "eager load" the students along with the subjects like this:
$subjects = Subjects::model()->with('Students')->findAll();
Here you are finding all of the subjects, but alerting Yii--using with('Students')--that you'll be wanting each subject's student information as well. This ensures that all of the students related to the subjects you find will be grabbed at once. An alternative to the with() function is to use a criteria's with property:
$criteria=new CDbCriteria;
$criteria->with = array('Students');
$subjects = Subjects::model()->findAll($criteria);
Either way, when you do ask for a subject's students like this:
$subjects[0]->Students;
$subjects[1]->Students;
// ...
you will not get another DB call each time because Yii already loaded the data.
You'll need to provide more details about what you are wanting to do with the students in the data provider before I can give any more details about that.