Many-to-many relation Laravel Eloquent. Fetch related table with specific related id

Question

I am writing a query in Laravel 8 using Eloquent. There is a many-to-many relation between subjects and streams and their pivot table is courses.

subjects: id name

streams id name

courses id subject_id stream_id

I have to fetch subjects with specific stream.

I have written the following query.

$this->subjects = Subject::has('streams',$this->stream)->get();

I am having problem in this.

courses table :

id	stream_id	subject_id
1	1	1
2	1	2
3	1	3
4	1	4
5	2	1
6	2	2
7	3	1

This is the sample data. If I want to fetch subject where stream id is 1 then it is only fetching subject with ids 3 and 4 and not fetching subjects with id 1 and 2. Can anyone explain me why it is skipping subject ids with 1 and 2 ?

PLease anyone can help me with this. Thank you in advance . :)

Edited

class Subject
{
   public function streams()
    {
        return $this->belongsToMany(Stream::class, 'courses', 
'subject_id', 'stream_id');
    }
}


class Stream
{
   public function subjects()
    {
        return $this->belongsToMany(Subject::class, 'courses', 
'stream_id', 'subject_id');
    }
}

Answer 1

For fetching models having a specific related model you can use whereHas() method. https://laravel.com/docs/8.x/eloquent-relationships#querying-relationship-existence

Assuming that $this->stream is a Stream model, you can use a closure for whereHas method:

$stream = $this->stream;

$this->subjects = Subject::whereHas('streams', function($query) use ($stream){
   $query->where('streams.id', $stream->id);
})->get();

Edit: since $this->stream is an id you should do

$stream = $this->stream;

$this->subjects = Subject::whereHas('streams', function($query) use ($stream){
   $query->where('streams.id', $stream);
})->get();