Eloquent with(), select() and where() selection - laravel

Question

This is my query to fetch data from 2 different table.
$variant = Variant::with(['v_detail' => function($q){
$q->select('variant_dtl_name');
}])->where('product_id','=',$productId)->get();
There is output, but v_detail returning empty list
result:
created_at: "2015-11-07 12:37:26"
id: 1
product_id: 30
updated_at: "2015-11-07 12:37:26"
v_detail: []
variant_name: "Pricing"
But with these query:
$variant = Variant::with('v_detail')->where('product_id','=',$productId)->get();
The result is:
created_at: "2015-11-07 12:37:26"
id: 1
product_id: 30
updated_at: "2015-11-07 12:37:26"
v_detail: [{id: 1, variant_id: 1, variant_dtl_name: "Adult", variant_dtl_price: 25,…},…]
0: {id: 1, variant_id: 1, variant_dtl_name: "Adult", variant_dtl_price: 25,…}
1: {id: 2, variant_id: 1, variant_dtl_name: "Senior", variant_dtl_price: 15,…}
2: {id: 3, variant_id: 1, variant_dtl_name: "Children", variant_dtl_price: 8,…}
variant_name: "Pricing"
Now, on the query that work, how can I fetch a specific column names. Thanks!!

Answer 1

You have this:
$variant = Variant::with(['v_detail' => function($q)
{
// Either add the related foreign key or select all
$q->select('related_foreign_key', 'variant_dtl_name');
}])->where('product_id','=',$productId)->get();
Since you are selecting only a single field which is variant_dtl_name then it's not possible to find out the related models because the relation builder foreign key is required. So, you have to select that foreign key as well. Notice the related_foreign_key in sub-query so use the right one, probably that is variant_id but not sure because you didn't mention anything about that.